# kb

id: encephalitis-lethargica-20260505-1
file: data/en.wikipedia.org/wiki/Encephalitis_lethargica-1.md
category: reference
title: Encephalitis lethargica
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Encephalitis_lethargica
date_saved: 2026-05-05T11:04:25.215156+00:00
instance: kb-cron
parent: encephalitis-lethargica-20260505-0
summary:
In 1580, Europe was swept by a serious febrile and lethargic illness that led to Parkinsonism and other neurological sequelae. From 1673 to 1675, a similar serious epidemic occurred in London, which Thomas Sydenham described as "febris comatosa". In 1695, a 20-year-old woman in Germany experienced oculogyric crises, Parkinsonism, diplopia, strabismus, and other symptoms following an attack of somnolent brain fever, as described by Albrecht of Hildesheim. In 1712–1713, a severe epidemic of Schlafkrankheit ('sleep sickness') occurred in Tübingen, Germany, followed in many cases by persistent slowness of movement and lack of initiative (aboulia). Between 1750 and 1800, France and Germany experienced minor epidemics of "coma somnolentum" with features of Parkinsonism, including hyperkinetic hiccup, myoclonus, chorea, and tics. Between 1848 and 1882, Paris-based neurologist Jean-Martin Charcot documented many isolated cases of juvenile Parkinsonism, associated with diplopia, oculogyria, tachypnoea, retropulsion, and obsessional disorders, which were almost certainly post-encephalitic in origin. In 1890 in Italy, following the influenza epidemic of 1889–1890, a severe epidemic of somnolent illnesses (nicknamed the "Nona") appeared. For the few survivors of the Nona, Parkinsonism and other sequelae developed in almost all cases. Between 1915 and 1927, a world-wide encephalitis lethargica pandemic occurred, impacting nearly 5 million people


id: facial-onset-sensory-and-motor-neuronopathy-20260505-0
file: data/en.wikipedia.org/wiki/Facial_onset_sensory_and_motor_neuronopathy-0.md
category: reference
title: Facial onset sensory and motor neuronopathy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Facial_onset_sensory_and_motor_neuronopathy
date_saved: 2026-05-05T11:04:26.390586+00:00
instance: kb-cron
parent: facial-onset-sensory-and-motor-neuronopathy-20260505-0
summary:
Facial onset sensory and motor neuronopathy, often abbreviated FOSMN, is a rare disorder of the nervous system in which sensory and motor nerves of the face and limbs progressively degenerate over a period of months to years. This degenerative process, the cause of which is unknown, eventually results in sensory and motor symptoms — the former consisting mainly of paresthesia followed by numbness, and the latter in muscle weakness, atrophy, and eventual paralysis. FOSM is characterized by sensory and motor loss beginning in the face and spreading to involve an increasingly larger area including the scalp, upper arms and trunk. The muscles or respiration and swallowing are commonly affected. In many ways, it is reminiscent of the much better known condition amyotrophic lateral sclerosis, with which it is closely related. There is no cure; treatment is supportive. Life expectancy may be shortened by respiratory complications arising from weakness of the muscles that aid breathing and swallowing. It was first described in four patients by Vucic and colleagues working at the Massachusetts General Hospital in the United States; subsequent reports from the United Kingdom, Europe and Asia point to a global incidence of the disease. It is thought to be exceptionally


id: fatal-insomnia-20260505-0
file: data/en.wikipedia.org/wiki/Fatal_insomnia-0.md
category: reference
title: Fatal insomnia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Fatal_insomnia
date_saved: 2026-05-05T11:04:27.568044+00:00
instance: kb-cron
parent: fatal-insomnia-20260505-0
summary:
Fatal insomnia is a neurodegenerative disease that results in trouble sleeping as its hallmark symptom. The majority of cases are familial (fatal familial insomnia [FFI]), stemming from a mutation in the PRNP gene, with the remainder of cases occurring sporadically (sporadic fatal insomnia [sFI]). The problems with sleeping typically start out gradually and worsen over time. Eventually, the patient will succumb to total insomnia (agrypnia excitata), most often leading to other symptoms such as speech problems, coordination problems, and dementia. It results in death within a few months to a few years, and there is no known disease-modifying treatment. == Signs and symptoms == The disease has four stages: Characterized by worsening insomnia, resulting in panic attacks, paranoia, and phobias. This stage lasts for about four months. Hallucinations and panic attacks become noticeable, continuing for about five months. Complete inability to sleep followed by rapid loss of weight. This lasts for about three months. Dementia, during which the person becomes unresponsive or mute over the course of six months, is the final stage of the disease, followed by death. Clinically, Fatal insomnia manifests with a disordered sleep-wake cycle, dysautonomia, motor disturbances, and neuropsychiatric disorders. Other symptoms include profuse sweating, miosis


id: fatal-insomnia-20260505-1
file: data/en.wikipedia.org/wiki/Fatal_insomnia-1.md
category: reference
title: Fatal insomnia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Fatal_insomnia
date_saved: 2026-05-05T11:04:27.568044+00:00
instance: kb-cron
parent: fatal-insomnia-20260505-0
summary:
=== Differential diagnosis === Other diseases involving the mammalian prion protein are known. Some are transmissible (TSEs, including FFI) such as kuru, bovine spongiform encephalopathy (BSE, also known as mad cow disease) in cattle and chronic wasting disease in American deer and American elk in some areas of the United States and Canada, as well as Creutzfeldt–Jakob disease (CJD). == Treatments == Treatment involves palliative care. There is conflicting evidence over the use of sleeping pills, including barbiturates, as a treatment for the disease. Symptoms of fatal familial insomnia may be treated with medications. Clonazepam may be prescribed to treat muscle spasms, and eszopiclone or zolpidem may be prescribed to help treat insomnia. However, these drugs do not work in the long term. == Prognosis == Like all prion diseases, FFI is invariably fatal. Life expectancy ranges from seven months to six years, with an average of 18 months. == Epidemiology and history == Fatal insomnia was first described by Elio Lugaresi et al. in 1986. In 1998, 40 families were known to carry the gene for FFI globally: eight German, five Italian, four American, two French, two Australian, two British, one Japanese and one Austrian. In the Basque Country


id: form-perception-20260505-0
file: data/en.wikipedia.org/wiki/Form_perception-0.md
category: reference
title: Form perception
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Form_perception
date_saved: 2026-05-05T11:04:28.772828+00:00
instance: kb-cron
parent: form-perception-20260505-0
summary:
Form perception is the recognition of visual elements of objects, specifically those to do with shapes, patterns and previously identified important characteristics. An object is perceived by the retina as a two-dimensional image, but the image can vary for the same object in terms of the context with which it is viewed, the apparent size of the object, the angle from which it is viewed, how illuminated it is, as well as where it resides in the field of vision. Despite the fact that each instance of observing an object leads to a unique retinal response pattern, the visual processing in the brain is capable of recognizing these experiences as analogous, allowing invariant object recognition. Visual processing occurs in a hierarchy with the lowest levels recognizing lines and contours, and slightly higher levels performing tasks such as completing boundaries and recognizing contour combinations. The highest levels integrate the perceived information to recognize an entire object. Essentially object recognition is the ability to assign labels to objects in order to categorize and identify them, thus distinguishing one object from another. During visual processing information is not created, but rather reformatted in a way that draws out the most detailed information of


id: form-perception-20260505-1
file: data/en.wikipedia.org/wiki/Form_perception-1.md
category: reference
title: Form perception
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Form_perception
date_saved: 2026-05-05T11:04:28.772828+00:00
instance: kb-cron
parent: form-perception-20260505-0
summary:
=== Injury and illness === Potential injuries to the brain include but are not limited to stroke, oxygen deprivation, blunt force trauma, and surgical injuries. When patients have lesions on their brain that develop as a result of injury or illness, such as multiple sclerosis or epilepsy, it is possible that they may have impaired object recognition which can manifest in the form of many different agnosias. Similar deficits have also been observed adults that have suffered blunt force trauma, strokes, severe carbon monoxide poisoning as well as in adults that have surgical damage following removal of tumors. Deficits have also been observed in children with types of epilepsy that do not lead to the formation of lesions. It is believed that in these cases the seizures cause a functional disruption that is capable of interfering with the processing of objects. Regions that specifically lead to deficits in object recognition when a lesion is present include the right lateral fusiform gyrus and the ventrolateral or ventromedial occipito-temporal cortex. These structures have all been identified as being crucial to the processing of shape and contour information, which is the basis for object recognition. Although people with damage to these structures are


id: memory-consolidation-20260505-0
file: data/en.wikipedia.org/wiki/Memory_consolidation-0.md
category: reference
title: Memory consolidation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Memory_consolidation
date_saved: 2026-05-05T11:04:29.928717+00:00
instance: kb-cron
parent: memory-consolidation-20260505-0
summary:
Memory consolidation is a process in the brain that stabilizes newly learned information, allowing the memory to be stored long-term. A memory trace is the biological change in neural circuits that occurs during learning. Memory consolidation is essential for learning as it allows experiences to be transformed into stable long-term memories that can guide future behavior. Consolidation is divided into two main processes, synaptic consolidation and systems consolidation. Synaptic consolidation occurs rapidly on a small scale in the individual synapses within the first few hours of learning. Systems consolidation occurs on a larger scale and involves gradual reorganization and reduced reliance on the hippocampus and increased involvement of cortical networks over a period of weeks to years. These processes involve molecular and cellular changes that stabilize neural representations, referred to as a neural ensemble (engram). A third process, reconsolidation, has been proposed, in which previously consolidated memories can become unstable again after retrieval and may need to be updated before being re-stabilized. == History == Memory consolidation was first referred to in the writings of the renowned Roman teacher of rhetoric Quintillian, who noted that memory improves over time. In the late 19th century, German researchers Müller and Alfons Pilzecker


id: memory-consolidation-20260505-1
file: data/en.wikipedia.org/wiki/Memory_consolidation-1.md
category: reference
title: Memory consolidation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Memory_consolidation
date_saved: 2026-05-05T11:04:29.928717+00:00
instance: kb-cron
parent: memory-consolidation-20260505-0
summary:
=== Protein synthesis === Protein synthesis has shown to play an important role in the formation of new memories. Studies have shown that protein synthesis inhibitors administered after learning weaken memory, suggesting that protein synthesis is required for memory consolidation. Additionally, reports have suggested that the effects of protein synthesis inhibitors also inhibit LTP. However, other results have shown that protein synthesis may not in fact be necessary for memory consolidation, as it has been found that the formation of memories can withstand vast amounts of protein synthesis inhibition, suggesting that its role may not be absolute. == Systems consolidation == Systems consolidation is the later phase of memory consolidation in which memories are reorganized across brain regions over time. Newly formed memories are first encoded in the hippocampus and then are gradually reorganized across cortical networks in a more permanent form of storage. Systems consolidation is a slow dynamic process which occurs over days to years as a gradual shift from hippocampus-dependent to hippocampus-independent memory storage. Systems consolidation is proposed to be involved in repeated reactivation of memory traces especially during sleep. The reactivations help strengthen the connections between cortical regions thereby gradually reducing reliance on the hippocampus. Over


id: memory-inhibition-20260505-0
file: data/en.wikipedia.org/wiki/Memory_inhibition-0.md
category: reference
title: Memory inhibition
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Memory_inhibition
date_saved: 2026-05-05T11:04:31.129532+00:00
instance: kb-cron
parent: memory-inhibition-20260505-0
summary:
In psychology, memory inhibition is the ability not to remember irrelevant information. The scientific concept of memory inhibition should not be confused with everyday uses of the word "inhibition". Scientifically speaking, memory inhibition is a type of cognitive inhibition, which is the stopping or overriding of a mental process, in whole or in part, with or without intention. Memory inhibition is a critical component of an effective memory system. While some memories are retained for a lifetime, most memories are forgotten. According to evolutionary psychologists, forgetting is adaptive because it facilitates selectivity of rapid, efficient recollection. For example, a person trying to remember where they parked their car would not want to remember every place they have ever parked. In order to remember something, therefore, it is essential not only to activate the relevant information, but also to inhibit irrelevant information. There are many memory phenomena that seem to involve inhibition, although there is often debate about the distinction between interference and inhibition. == History == In the early days of psychology, the concept of inhibition was prevalent and influential (e.g., Breese, 1899; Pillsbury, 1908; Wundt, 1902). These psychologists applied the concept of inhibition (and interference) to early theories of


id: memory-inhibition-20260505-1
file: data/en.wikipedia.org/wiki/Memory_inhibition-1.md
category: reference
title: Memory inhibition
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Memory_inhibition
date_saved: 2026-05-05T11:04:31.129532+00:00
instance: kb-cron
parent: memory-inhibition-20260505-0
summary:
=== "Think/no-think" paradigm and intentional inhibition === During the recovered memory debate of the 1990s, cognitive psychologists were dubious about whether specific memories could be repressed. One stumbling block was that repression had not been demonstrated in a research study. In 2001, researchers Anderson and Green claimed to have found laboratory evidence of suppression. They trained their participants with a list of unrelated word pairs (such as ordeal-roach), so they could respond with the second member of the pair (roach) when they saw the other member (ordeal). The more frequently participants had tried to not think about a particular word, the less likely they were to retrieve it on a final memory test. This impairment even occurred when participants were given an "independent probe" test, i.e. given a similar category (insect) instead of the original cue (roach), and asked to fill in the blank on the memory test: insect-r_____. According to Anderson and Green, the fact that participants had a decreased ability to recall items they were told to forget strongly supports the existence of an inhibitory control mechanism and the idea that people have the ability to suppress unwanted memories. Though Anderson & Green's (2001) results have been replicated


id: phantom-vibration-syndrome-20260505-0
file: data/en.wikipedia.org/wiki/Phantom_vibration_syndrome-0.md
category: reference
title: Phantom vibration syndrome
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Phantom_vibration_syndrome
date_saved: 2026-05-05T11:04:32.333444+00:00
instance: kb-cron
parent: phantom-vibration-syndrome-20260505-0
summary:
Phantom vibration syndrome or phantom ringing syndrome is the perception that one's mobile phone is vibrating or ringing when it is not. Other terms for this concept include ringxiety (a portmanteau of ring and anxiety), fauxcellarm (a portmanteau of "faux" /foʊ/ meaning "fake" or "false" and "cellphone" and "alarm" pronounced similarly to "false alarm"), phonetom (a portmanteau of phone and phantom) and phantom phone signals. According to Michael Rothberg, it is not a syndrome, but is better characterised as a tactile hallucination since the brain perceives a sensation that is not actually present. WebMD published an article on phantom vibration syndrome with Rothberg as a source. Several other articles have been published in 2010s, including in NPR, Bustle, CBS News, and Psychology Today. Phantom ringing may be experienced while taking a shower, watching television, or using a noisy device. Humans are particularly sensitive to auditory tones between 1,000 and 6,000 hertz, and basic mobile phone ringtones often fall within this range. Phantom vibrations develop after carrying a cell phone set to use vibrating alerts. Researcher Michelle Drouin found that almost 9 out of 10 undergraduates at her college experienced phantom vibrations. == History == In the comic strip Dilbert, cartoonist


id: posterior-cortical-atrophy-20260505-0
file: data/en.wikipedia.org/wiki/Posterior_cortical_atrophy-0.md
category: reference
title: Posterior cortical atrophy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Posterior_cortical_atrophy
date_saved: 2026-05-05T11:04:33.570892+00:00
instance: kb-cron
parent: posterior-cortical-atrophy-20260505-0
summary:
Posterior cortical atrophy (PCA), also called Benson's syndrome, is a rare form of dementia which is considered a visual variant or an atypical variant of Alzheimer's disease (AD). The disease causes atrophy of the posterior part of the cerebral cortex, resulting in the progressive disruption of complex visual processing. PCA was first described by D. Frank Benson in 1988. PCA usually affects people at an earlier age than typical cases of Alzheimer's disease, with initial symptoms often experienced in people in their mid-fifties or early sixties. This was the case with writer Terry Pratchett (1948–2015), who went public in 2007 about being diagnosed with PCA. In rare cases, PCA can be caused by dementia with Lewy bodies and Creutzfeldt–Jakob disease. == Symptoms == The main symptom resulting from posterior cortical atrophy is a decrease in visuospatial and visuoperceptual capabilities, since the area of atrophy involves the occipital lobe responsible for visual processing. The atrophy is progressive; early symptoms include difficulty reading, blurred vision, light sensitivity, issues with depth perception, and trouble navigating through space. Additional symptoms include apraxia, a disorder of movement planning, alexia, an impaired ability to read, and visual agnosia, an object recognition disorder. In the two-streams hypothesis,


id: postvaccinal-encephalitis-20260505-0
file: data/en.wikipedia.org/wiki/Postvaccinal_encephalitis-0.md
category: reference
title: Postvaccinal encephalitis
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Postvaccinal_encephalitis
date_saved: 2026-05-05T11:04:34.702052+00:00
instance: kb-cron
parent: postvaccinal-encephalitis-20260505-0
summary:
Postvaccinal encephalitis (PVE) is a rare complication which was associated with vaccination with vaccinia virus during the worldwide smallpox eradication campaign. With mortality ranging between 25 – 30% it is the most severe adverse event associated with this vaccination. The mechanism of how it happens is unknown. == Symptoms and signs == PVE symptoms start to appear between 8th and 14th day after vaccination. Amongst the first are fever, headache, confusion and nausea. With passing time lethargy, seizures, short and long term memory dysfunctions, localized paralysis, hemiplegia, polyneuritis and convulsions. In extreme cases PVE can lead to coma and death. == Histology == Inflammatory extra-adventitial lesions are found not only in the brain but in the spinal cord as well. Lesions might be uniform in acute phase or disseminated in subacute phase. Unlike in cases of encephalitis lethargica the main damage is found in white brain matter. Meninges are infiltrated with T cells, plasmatic cells and phagocytic cells. Polymorfonuclear cells were found only in severe lesions. Apart from cellular infiltrate in perivascular space there is a tissue rarefication in spaces close to damaged blood vessels. Accumulated small nuclei are found in places of such rarefication. Strong demyelination with rapid clearance


id: progressive-muscular-atrophy-20260505-0
file: data/en.wikipedia.org/wiki/Progressive_muscular_atrophy-0.md
category: reference
title: Progressive muscular atrophy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Progressive_muscular_atrophy
date_saved: 2026-05-05T11:04:35.927722+00:00
instance: kb-cron
parent: progressive-muscular-atrophy-20260505-0
summary:
Progressive muscular atrophy (PMA), also called Duchenne–Aran disease and Duchenne–Aran muscular atrophy, is a disorder characterized by the degeneration of lower motor neurons, resulting in generalized, progressive loss of muscle function. PMA is classified among motor neuron diseases (MND) and it sporadically appears during adulthood. It is speculated that about 2.5%-11% of adult onset MND is PMA, making it less common than ALS. PMA affects only the lower motor neurons, in contrast to amyotrophic lateral sclerosis (ALS), the most common MND, which affects both the upper and lower motor neurons, or primary lateral sclerosis, another MND, which affects only the upper motor neurons. The history of PMA involved determining if it was a separate disease from ALS or if it was just the earlier stages of ALS. Eventually, scientists concluded that PMA was its own disease under the same category as ALS. The signs and symptoms of PMA are similar to ALS, but are located in a different region of the body. Additionally, the diagnosis can be more complex due to the nature of PMA and ALS. The prognosis of PMA can be longer than ALS because it affects less of the motor neurons. The options for treatment are small


id: progressive-muscular-atrophy-20260505-1
file: data/en.wikipedia.org/wiki/Progressive_muscular_atrophy-1.md
category: reference
title: Progressive muscular atrophy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Progressive_muscular_atrophy
date_saved: 2026-05-05T11:04:35.927722+00:00
instance: kb-cron
parent: progressive-muscular-atrophy-20260505-0
summary:
The prognosis is a little better. A recent study found the 5-year survival rate in PMA to be 33% (vs 20% in ALS) and the 10-year survival rate to be 12% (vs 6% in ALS). Patients with PMA do not have the cognitive change identified in certain groups of patients with MND. Because PMA patients do not have UMN signs, they usually do not meet the World Federation of Neurology El Escorial Research Criteria for "Definite" or "Probable" ALS and so are ineligible to participate in the majority of clinical trials conducted in ALS. Because of its rarity (even compared to ALS) and confusion about the condition, some insurance policies or local healthcare policies may not recognize PMA as being the life-changing illness that it is. In cases where being classified as being PMA rather than ALS is likely to restrict access to services, it may be preferable to be diagnosed as "slowly progressive ALS" or "lower motor neuron predominant" ALS. An initial diagnosis of PMA could turn out to be slowly progressive ALS many years later, sometimes even decades after the initial diagnosis. The occurrence of upper motor neuron symptoms such as brisk reflexes, spasticity, or a Babinski sign


id: qualia-20260505-0
file: data/en.wikipedia.org/wiki/Qualia-0.md
category: reference
title: Qualia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Qualia
date_saved: 2026-05-05T11:04:37.131418+00:00
instance: kb-cron
parent: qualia-20260505-0
summary:
In philosophy of mind, qualia (; singular: quale ) are defined as instances of subjective experience. The term qualia derives from the Latin neuter plural form (qualia) of the Latin adjective quālis (Latin pronunciation: [ˈkʷaːlɪs]) meaning "of what sort" or "of what kind" in relation to a specific instance, such as "what it is like to taste a specific apple — this particular apple now". Examples of qualia include the perceived sensation of pain of a headache, the taste of wine, and the redness of an evening sky. As qualitative characteristics of sensations, qualia stand in contrast to propositional attitudes, where the focus is on beliefs about experience rather than what it is directly like to be experiencing. C.S. Peirce introduced the term quale in philosophy in 1866, and in 1929 C. I. Lewis was the first to use the term "qualia" in its generally agreed-upon modern sense. Frank Jackson later defined qualia as "...certain features of the bodily sensations especially, but also of certain perceptual experiences, which no amount of purely physical information includes". Philosopher and cognitive scientist Daniel Dennett suggested that qualia was "an unfamiliar term for something that could not be more familiar to each of us:


id: qualia-20260505-1
file: data/en.wikipedia.org/wiki/Qualia-1.md
category: reference
title: Qualia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Qualia
date_saved: 2026-05-05T11:04:37.131418+00:00
instance: kb-cron
parent: qualia-20260505-0
summary:
The inverted spectrum thought experiment, originally developed by John Locke, invites us to imagine two individuals who perceive colors differently: where one person sees red, the other sees green, and vice versa. Despite this difference in their subjective experiences, they behave and communicate as if their perceptions are the same, and no physical or behavioral test can reveal the inversion. Critics of functionalism, and of physicalism more broadly, argue that if we can imagine this happening without contradiction, it follows that we are imagining a change in a property that determines the way things look to us, but that has no physical basis. The idea that an inverted spectrum would be undetectable in practice is also open to criticism on more scientific grounds, by C. L. Hardin, among others. As Alex Byrne puts it: ...there are more perceptually distinguishable shades between red and blue than there are between green and yellow, which would make red-green inversion behaviorally detectable. And there are yet further asymmetries. Dark yellow is brown (qualitatively different from yellow), whereas dark blue is blue[...] Similarly, desaturated bluish-red is pink (qualitatively different from saturated bluish-red), whereas desaturated greenish-yellow is similar to saturated greenish-yellow. Again, red is a "warm"


id: qualia-20260505-2
file: data/en.wikipedia.org/wiki/Qualia-2.md
category: reference
title: Qualia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Qualia
date_saved: 2026-05-05T11:04:37.131418+00:00
instance: kb-cron
parent: qualia-20260505-0
summary:
Joseph Levine's paper Conceivability, Identity, and the Explanatory Gap takes up where the criticisms of conceivability arguments (such as the inverted spectrum argument and the zombie argument) leave off. Levine agrees that conceivability is a flawed means of establishing metaphysical realities, but points out that even if we come to the metaphysical conclusion that qualia are physical, there is still an explanatory problem. While I think this materialist response is right in the end, it does not suffice to put the mind-body problem to rest. Even if conceivability considerations do not establish that the mind is in fact distinct from the body, or that mental properties are metaphysically irreducible to physical properties, still they do demonstrate that we lack an explanation of the mental in terms of the physical. However, such an epistemological or explanatory problem might indicate an underlying metaphysical issue, as even if not proven by conceivability arguments, the non-physicality of qualia is far from ruled out. In the end, we are right back where we started. The explanatory gap argument doesn't demonstrate a gap in nature, but a gap in our understanding of nature. Of course a plausible explanation for there being a gap in our understanding


id: qualia-20260505-3
file: data/en.wikipedia.org/wiki/Qualia-3.md
category: reference
title: Qualia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Qualia
date_saved: 2026-05-05T11:04:37.131418+00:00
instance: kb-cron
parent: qualia-20260505-0
summary:
==== E. J. Lowe ==== E. J. Lowe denies that indirect realism, wherein which we have access only to sensory features internal to the brain, necessarily implies a Cartesian dualism. He agrees with Bertrand Russell that the way images are received by our retinas, our "retinal images", are connected to "patterns of neural activity in the cortex". He defends a version of the causal theory of perception in which a causal path can be traced between the external object and the perception of it. He is careful to deny that we do any inferring from the sensory field; he believes this allows us to build an access to knowledge on that causal connection. In a later work he moves closer to the non-epistemic argument in that he postulates "a wholly non-conceptual component of perceptual experience". ==== J. B. Maund ==== John Barry Maund, an Australian philosopher of perception, argues that qualia can be described on two levels, a fact that he refers to as "dual coding". Maund extended his argument with reference to color. Color he sees as a dispositional property, not an objective one. Colors are "virtual properties", which means they are as if things possessed them. Although the


id: qualia-20260505-4
file: data/en.wikipedia.org/wiki/Qualia-4.md
category: reference
title: Qualia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Qualia
date_saved: 2026-05-05T11:04:37.131418+00:00
instance: kb-cron
parent: qualia-20260505-0
summary:
Vilayanur S. Ramachandran and William Hirstein proposed three laws of qualia (with a fourth later added), which are "functional criteria that need to be fulfilled in order for certain neural events to be associated with qualia" by philosophers of the mind: Qualia are irrevocable and indubitable. You don't say 'maybe it is red but I can visualize it as green if I want to'. An explicit neural representation of red is created that invariably and automatically 'reports' this to higher brain centres. Once the representation is created, what can be done with it is open-ended. You have the luxury of choice, e.g., if you have the percept of an apple you can use it to tempt Adam, to keep the doctor away, bake a pie, or just to eat. Even though the representation at the input level is immutable and automatic, the output is potentially infinite. This isn't true for, say, a spinal reflex arc where the output is also inevitable and automatic. Indeed, a paraplegic can even have an erection and ejaculate without an orgasm. Short-term memory. The input invariably creates a representation that persists in short-term memory – long enough to allow time for choice of output. Without


id: qualia-20260505-5
file: data/en.wikipedia.org/wiki/Qualia-5.md
category: reference
title: Qualia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Qualia
date_saved: 2026-05-05T11:04:37.131418+00:00
instance: kb-cron
parent: qualia-20260505-0
summary:
Dennett attempts to show that we cannot satisfy (a) either through introspection or through observation, and that qualia's very definition undermines its chances of satisfying (b). Supporters of qualia point out that in order for you to notice a change in qualia, you must compare your current qualia with your memories of past qualia. Arguably, such a comparison would involve immediate assessment of your current qualia and your memories of past qualia, but not of the past qualia themselves. Furthermore, modern functional brain imaging has increasingly suggested that the memory of an experience is processed in similar ways, and in similar zones of the brain, as the original perception. This may mean that there would be asymmetric outcomes between altering the mechanism of perception of qualia and altering the memory of that qualia. If the diabolical neurosurgery altered the immediate perception of qualia, the inversion might not be noticed directly, since the brain zones which re-process the memories would invert the remembered qualia. On the other hand, alteration of the qualia memories themselves would be processed without inversion, and thus you would perceive them as an inversion. Thus, you might know immediately if memory of your qualia had been altered,


id: qualia-20260505-6
file: data/en.wikipedia.org/wiki/Qualia-6.md
category: reference
title: Qualia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Qualia
date_saved: 2026-05-05T11:04:37.131418+00:00
instance: kb-cron
parent: qualia-20260505-0
summary:
=== Paul Churchland === According to Paul Churchland, Mary might be considered akin to a feral child who suffered extreme isolation during childhood. Technically when Mary leaves the room, she would not have the ability to see or know what the color red is, as a brain has to learn and develop how to see colors. Patterns need to form in the V4 section of the visual cortex, which occurs via exposure to wavelengths of light. This exposure needs to occur during the early stages of brain development. In Mary's case, the identifications and categorizations of color will only be in respect to representations of black and white. === Gary Drescher === In his book Good and Real, Gary Drescher compares qualia with "gensyms" (generated symbols) in Common Lisp. These are objects that Lisp treats as having no properties or components, which can only be identified as equal or not equal to other objects. Drescher explains, "we have no introspective access to whatever internal properties make the red gensym recognizably distinct from the green [...] even though we know the sensation when we experience it." Under this interpretation of qualia, Drescher responds to the Mary thought experiment by noting that


id: qualia-20260505-7
file: data/en.wikipedia.org/wiki/Qualia-7.md
category: reference
title: Qualia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Qualia
date_saved: 2026-05-05T11:04:37.131418+00:00
instance: kb-cron
parent: qualia-20260505-0
summary:
"[T]he purportedly metaphysical "problem of consciousness" is no more and no less than the epistemological "problem of privileged access," and that once this is seen questions about dualism versus materialism lose their interest." Rorty suggests that the only answer that one can give as to why qualia are ontologically distinct from physical processes is that the lack of an appearance/reality distinction is an essential feature of their being (i.e. it is an essential feature of a quale that it be incorrigibly known), but he notes that in making this move, qualia have been hypostatized such that they can take on the property of being pure appearances. In other words, they have been turned into non-physical, property-bearing particulars, meaning they are no longer properties of the person who has them, but rather particulars that exist in addition to that person. Thus, the dualistic intuition that an explanation of, say, pain in terms of physical functions and behaviors leaves out the raw feel of pain itself is the result of hypostatizing pain into something non-physical which accompanies those physical processes: "The neo-dualist who identifies a pain with how it feels to be in pain is hypostatizing a property—painfulness—into a special sort of


id: qualia-20260505-8
file: data/en.wikipedia.org/wiki/Qualia-8.md
category: reference
title: Qualia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Qualia
date_saved: 2026-05-05T11:04:37.131418+00:00
instance: kb-cron
parent: qualia-20260505-0
summary:
"Poised" - the phenomenal experience is always present to the understanding, whether or not the agent is able to apply a concept to it. "Abstract" - it is unclear whether you are in touch with a concrete object (for example, someone may feel a pain in an amputated limb). "Nonconceptual" - phenomenon can exist although one does not have the concept by which to recognize it. "Intentional (Content)" - it represents something, whether or not the observer is taking advantage of that fact. Tye adds that the experience is like a map in that, in most cases, it goes beyond the shapes, edges, volumes, etc. in the world – you may not be reading the a map but, as with an actual map there is a reliable match with what it is mapping. This is why Tye calls his theory representationalism, makes it plain that Tye believes that he has retained a direct contact with what produces the phenomena and is therefore not hampered by any trace of a "veil of perception". == See also == == References == === Citations === === Other references === Various authors (19 March 2007). Chalmers, David (ed.). "Online collection of papers on qualia".


id: sleep-onset-20260505-0
file: data/en.wikipedia.org/wiki/Sleep_onset-0.md
category: reference
title: Sleep onset
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Sleep_onset
date_saved: 2026-05-05T11:04:38.285135+00:00
instance: kb-cron
parent: sleep-onset-20260505-0
summary:
Sleep onset is the transition from wakefulness into sleep. Sleep onset usually transits into non-rapid eye movement sleep (NREM sleep) but under certain circumstances (e.g. narcolepsy) it is possible to transit from wakefulness directly into rapid eye movement sleep (REM sleep). == History == During the 1920s an obscure disorder that caused encephalitis and attacked the part of the brain that regulates sleep influenced Europe and North America. Although the virus that caused this disorder was never identified, the psychiatrist and neurologist Constantin von Economo decided to study this disease and identified a key component in the sleep-wake regulation. He identified the pathways that regulated wakefulness and sleep onset by studying the parts of the brain that were affected by the disease and the consequences it had on the circadian rhythm. He stated that the pathways that regulated sleep onset are located between the brain stem and the basal forebrain. His discoveries were not appreciated until the last two decades of the 20th century when the pathways of sleep were found to reside in the exact place that Constantin von Economo stated. == Neural circuit == Sleep electrophysiological measurements can be made by attaching electrodes to the scalp to measure


id: subacute-sclerosing-panencephalitis-20260505-0
file: data/en.wikipedia.org/wiki/Subacute_sclerosing_panencephalitis-0.md
category: reference
title: Subacute sclerosing panencephalitis
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Subacute_sclerosing_panencephalitis
date_saved: 2026-05-05T11:04:39.501994+00:00
instance: kb-cron
parent: subacute-sclerosing-panencephalitis-20260505-0
summary:
Subacute sclerosing panencephalitis (SSPE), also known as Dawson disease, is a rare form of progressive brain inflammation caused by a persistent infection with the measles virus. The condition primarily affects children, teens, and young adults. It has been estimated that about 2 in 10,000 people who get measles will eventually develop SSPE. However, a 2016 study estimated that the rate for unvaccinated infants under 15 months was as high as 1 in 609. No cure for SSPE exists, and the condition is almost always fatal. SSPE is sometimes confused with acute disseminated encephalomyelitis, which can also be caused by the measles virus, but has a very different timing and course. SSPE is caused by some strains of the wild-type (naturally occurring) measles virus, such as the B3 strain, but not by the strains used in measles vaccines. == Signs and symptoms == SSPE is characterized by a history of primary measles infection, followed by a normal, unremarkable recovery. Symptoms of SSPE appear later. On average, the first symptoms appear about 10 years after the initial infection, though this varies significantly, as some people have developed SSPE symptoms as soon as 1 month after infection, and others as long as 27


id: thought-20260505-0
file: data/en.wikipedia.org/wiki/Thought-0.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
In their most common sense, thought and thinking refer to cognitive processes that occur independently of direct sensory stimulation. Core forms include judging, reasoning, concept formation, problem solving, and deliberation. Other processes, such as entertaining an idea, memory, or imagination, are also frequently considered types of thought. Unlike perception, these activities can occur without immediate input from the sensory organs. In a broader sense, any mental event—including perception and unconscious processes—may be described as a form of thought. The term can also denote not the process itself, but the resulting mental states or systems of ideas. A variety of theories attempt to explain the nature of thinking. Platonism holds that thought involves discerning eternal forms and their interrelations, distinguishing these pure entities from their imperfect sensory imitations. Aristotelianism interprets thinking as instantiating the universal essence of an object within the mind, derived from sense experience rather than a changeless realm. Conceptualism, closely related to Aristotelianism, identifies thinking with the mental evocation of concepts. Inner speech theories suggest that thought takes the form of silent verbal expression, sometimes in a natural language and sometimes in a specialized "mental language," or Mentalese, as proposed by the language of thought hypothesis. Associationism views


id: thought-20260505-1
file: data/en.wikipedia.org/wiki/Thought-1.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Aristotelianism and conceptualism === According to Aristotelianism, the mind thinks about an object by instantiating its essence. For example, when thinking about trees, the mind instantiates "tree-ness." Unlike actual trees, this instantiation does not occur in matter but in the mind, though the universal essence is the same in both cases. In contrast with Platonism, universals are not seen as timeless forms existing in a separate intelligible realm. Instead, they exist only insofar as they are instantiated. The mind comes to recognize universals through abstraction from experience, a view that avoids some objections directed against Platonism. Conceptualism is closely related. It holds that thinking consists in mentally evoking concepts. While some concepts may be innate, most are acquired through abstraction from sensory experience before they can be used in thought. Critics argue that both theories face difficulties. One problem is explaining the logical structure of thought. For instance, to think that it will either rain or snow, it is not enough to instantiate the essences of rain and snow or to evoke the relevant concepts. The disjunctive relation between them is not captured in this way. Another challenge lies in providing a clear account of how the mind acquires


id: thought-20260505-2
file: data/en.wikipedia.org/wiki/Thought-2.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Associationism === An important view in the empiricist tradition has been associationism, the view that thinking consists in the succession of ideas or images. This succession is seen as being governed by laws of association, which determine how the train of thought unfolds. These laws are different from logical relations between the contents of thoughts, which are found in the case of drawing inferences by moving from the thought of the premises to the thought of the conclusion. Various laws of association have been suggested. According to the laws of similarity and contrast, ideas tend to evoke other ideas that are either very similar to them or their opposite. The law of contiguity, on the other hand, states that if two ideas were frequently experienced together, then the experience of one tends to cause the experience of the other. In this sense, the history of an organism's experience determines which thoughts the organism has and how these thoughts unfold. But such an association does not guarantee that the connection is meaningful or rational. For example, because of the association between the terms "cold" and "Idaho", the thought "this coffee shop is cold" might lead to the thought "Russia should


id: thought-20260505-3
file: data/en.wikipedia.org/wiki/Thought-3.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Computationalism === Computationalist theories of thinking, often found in the cognitive sciences, understand thinking as a form of information processing. These views developed with the rise of computers in the second part of the 20th century, when various theorists saw thinking in analogy to computer operations. On such views, the information may be encoded differently in the brain, but in principle, the same operations take place there as well, corresponding to the storage, transmission, and processing of information. But while this analogy has some intuitive attraction, theorists have struggled to give a more explicit explanation of what computation is. A further problem consists in explaining the sense in which thinking is a form of computing. The traditionally dominant view defines computation in terms of Turing machines, though contemporary accounts often focus on neural networks for their analogies. A Turing machine is capable of executing any algorithm based on a few very basic principles, such as reading a symbol from a cell, writing a symbol to a cell, and executing instructions based on the symbols read. This way it is possible to perform deductive reasoning following the inference rules of formal logic as well as simulating many other functions of


id: thought-20260505-4
file: data/en.wikipedia.org/wiki/Thought-4.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Entertaining, judging, and reasoning === Thinking is often identified with the act of judging. A judgment is a mental operation in which a proposition is evoked and then either affirmed or denied. It involves deciding what to believe and aims at determining whether the judged proposition is true or false. Various theories of judgment have been proposed. The traditionally dominant approach is the combination theory. It states that judgments consist in the combination of concepts. On this view, to judge that "all men are mortal" is to combine the concepts "man" and "mortal". The same concepts can be combined in different ways, corresponding to different forms of judgment, for example, as "some men are mortal" or "no man is mortal". Other theories of judgment focus more on the relation between the judged proposition and reality. According to Franz Brentano, a judgment is either a belief or a disbelief in the existence of some entity. In this sense, there are only two fundamental forms of judgment: "A exists" and "A does not exist". When applied to the sentence "all men are mortal", the entity in question is "immortal men", of whom it is said that they do not exist. Important


id: thought-20260505-5
file: data/en.wikipedia.org/wiki/Thought-5.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Problem solving === In the case of problem solving, thinking aims at reaching a predefined goal by overcoming certain obstacles. This process often involves two different forms of thinking. On the one hand, divergent thinking aims at coming up with as many alternative solutions as possible. On the other hand, convergent thinking tries to narrow down the range of alternatives to the most promising candidates. Some researchers identify various steps in the process of problem solving. These steps include recognizing the problem, trying to understand its nature, identifying general criteria the solution should meet, deciding how these criteria should be prioritized, monitoring the progress, and evaluating the results. An important distinction concerns the type of problem that is faced. For well-structured problems, it is easy to determine which steps need to be taken to solve them, but executing these steps may still be difficult. For ill-structured problems, on the other hand, it is not clear what steps need to be taken, i.e. there is no clear formula that would lead to success if followed correctly. In this case, the solution may sometimes come in a flash of insight in which the problem is suddenly seen in a new light.


id: thought-20260505-6
file: data/en.wikipedia.org/wiki/Thought-6.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Unconscious thought === Conscious thought is the paradigmatic form of thinking and is often the focus of the corresponding research. But it has been argued that some forms of thought also happen on the unconscious level. Unconscious thought is thought that happens in the background without being experienced. It is therefore not observed directly. Instead, its existence is usually inferred by other means. For example, when someone is faced with an important decision or a difficult problem, they may not be able to solve it straight away. But then, at a later time, the solution may suddenly flash before them even though no conscious steps of thinking were taken towards this solution in the meantime. In such cases, the cognitive labor needed to arrive at a solution is often explained in terms of unconscious thoughts. The central idea is that a cognitive transition happened and we need to posit unconscious thoughts to be able to explain how it happened. It has been argued that conscious and unconscious thoughts differ not just concerning their relation to experience but also concerning their capacities. According to unconscious thought theorists, for example, conscious thought excels at simple problems with few variables but is


id: thought-20260505-7
file: data/en.wikipedia.org/wiki/Thought-7.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Phenomenology === Phenomenology is the science of the structure and contents of experience. The term "cognitive phenomenology" refers to the experiential character of thinking or what it feels like to think. Some theorists claim that there is no distinctive cognitive phenomenology. On such a view, the experience of thinking is just one form of sensory experience. According to one version, thinking just involves hearing a voice internally. According to another, there is no experience of thinking apart from the indirect effects thinking has on sensory experience. A weaker version of such an approach allows that thinking may have a distinct phenomenology but contends that thinking still depends on sensory experience because it cannot occur on its own. On this view, sensory contents constitute the foundation from which thinking may arise. An often-cited thought experiment in favor of the existence of a distinctive cognitive phenomenology involves two persons listening to a radio broadcast in French, one who understands French and the other who does not. The idea behind this example is that both listeners hear the same sounds and therefore have the same non-cognitive experience. In order to explain the difference, a distinctive cognitive phenomenology has to be posited: only


id: thought-20260505-8
file: data/en.wikipedia.org/wiki/Thought-8.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Metaphysics === The mind–body problem concerns the explanation of the relationship that exists between minds, or mental processes, and bodily states or processes. The main aim of philosophers working in this area is to determine the nature of the mind and mental states/processes, and how—or even if—minds are affected by and can affect the body. Human perceptual experiences depend on stimuli which arrive at one's various sensory organs from the external world and these stimuli cause changes in one's mental state, ultimately causing one to feel a sensation, which may be pleasant or unpleasant. Someone's desire for a slice of pizza, for example, will tend to cause that person to move his or her body in a specific manner and in a specific direction to obtain what he or she wants. The question, then, is how it can be possible for conscious experiences to arise out of a lump of gray matter endowed with nothing but electrochemical properties. A related problem is to explain how someone's propositional attitudes (e.g. beliefs and desires) can cause that individual's neurons to fire and his muscles to contract in exactly the correct manner. These comprise some of the puzzles that have confronted epistemologists


id: thought-20260505-9
file: data/en.wikipedia.org/wiki/Thought-9.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
The "id", "ego" and "super-ego" are the three parts of the "psychic apparatus" defined in Sigmund Freud's structural model of the psyche; they are the three theoretical constructs in terms of whose activity and interaction mental life is described. According to this model, the uncoordinated instinctual trends are encompassed by the "id", the organized realistic part of the psyche is the "ego", and the critical, moralizing function is the "super-ego". For psychoanalysis, the unconscious does not include all that is not conscious, rather only what is actively repressed from conscious thought or what the person is averse to knowing consciously. In a sense this view places the self in relationship to their unconscious as an adversary, warring with itself to keep what is unconscious hidden. If a person feels pain, all he can think of is alleviating the pain. Any of his desires, to get rid of pain or enjoy something, command the mind what to do. For Freud, the unconscious was a repository for socially unacceptable ideas, wishes or desires, traumatic memories, and painful emotions put out of mind by the mechanism of psychological repression. However, the contents did not necessarily have to be solely negative. In the psychoanalytic


id: thought-20260505-10
file: data/en.wikipedia.org/wiki/Thought-10.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Counterfactual thinking === Counterfactual thinking involves mental representations of non-actual situations and events, i.e. of what is "contrary to the facts". It is usually conditional: it aims at assessing what would be the case if a certain condition had obtained. In this sense, it tries to answer "What if"-questions. For example, thinking after an accident that one would be dead if one had not used the seatbelt is a form of counterfactual thinking: it assumes, contrary to the facts, that one had not used the seatbelt and tries to assess the result of this state of affairs. In this sense, counterfactual thinking is normally counterfactual only to a small degree since just a few facts are changed, like concerning the seatbelt, while most other facts are kept in place, like that one was driving, one's gender, the laws of physics, etc. When understood in the widest sense, there are forms of counterfactual thinking that do not involve anything contrary to the facts at all. This is the case, for example, when one tries to anticipate what might happen in the future if an uncertain event occurs and this event actually occurs later and brings with it the anticipated consequences.


id: thought-20260505-11
file: data/en.wikipedia.org/wiki/Thought-11.md
category: reference
title: Thought
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Thought
date_saved: 2026-05-05T11:04:40.951647+00:00
instance: kb-cron
parent: thought-20260505-0
summary:
=== Critical thinking === Critical thinking is a form of thinking that is reasonable, reflective, and focused on determining what to believe or how to act. It holds itself to various standards, like clarity and rationality. In this sense, it involves not just cognitive processes trying to solve the issue at hand but at the same time meta-cognitive processes ensuring that it lives up to its own standards. This includes assessing both that the reasoning itself is sound and that the evidence it rests on is reliable. This means that logic plays an important role in critical thinking. It concerns not just formal logic, but also informal logic, specifically to avoid various informal fallacies due to vague or ambiguous expressions in natural language. No generally accepted standard definition of "critical thinking" exists but there is significant overlap between the proposed definitions in their characterization of critical thinking as careful and goal-directed. According to some versions, only the thinker's own observations and experiments are accepted as evidence in critical thinking. Some restrict it to the formation of judgments but exclude action as its goal. A concrete everyday example of critical thinking, due to John Dewey, involves observing foam bubbles moving in


id: unihemispheric-slow-wave-sleep-20260505-0
file: data/en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep-0.md
category: reference
title: Unihemispheric slow-wave sleep
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep
date_saved: 2026-05-05T11:04:43.626925+00:00
instance: kb-cron
parent: unihemispheric-slow-wave-sleep-20260505-0
summary:
Unihemispheric slow-wave sleep (USWS) is sleep where one half of the brain rests while the other half remains alert. This is in contrast to normal sleep where both eyes are shut and both halves of the brain show unconsciousness. In USWS, also known as asymmetric slow-wave sleep, one half of the brain is in deep sleep, a form of non-rapid eye movement sleep and the eye corresponding to this half is closed while the other eye remains open. When examined by electroencephalography (EEG), the characteristic slow-wave sleep tracings are seen from one side while the other side shows a characteristic tracing of wakefulness. The phenomenon has been observed in a number of terrestrial, aquatic and avian species. Unique physiology, including the differential release of the neurotransmitter acetylcholine, has been linked to the phenomenon. USWS offers a number of benefits, including the ability to rest in areas of high predation or during long migratory flights. The behaviour remains an important research topic because USWS is possibly the first animal behaviour which uses different regions of the brain to simultaneously control sleep and wakefulness. The greatest theoretical importance of USWS is its potential role in elucidating the function of sleep by challenging


id: unihemispheric-slow-wave-sleep-20260505-1
file: data/en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep-1.md
category: reference
title: Unihemispheric slow-wave sleep
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep
date_saved: 2026-05-05T11:04:43.626925+00:00
instance: kb-cron
parent: unihemispheric-slow-wave-sleep-20260505-0
summary:
=== Eye opening === In domestic chicks and other species of birds exhibiting USWS, one eye remained open contra-lateral (on the opposite side) to the "awake" hemisphere. The closed eye was shown to be opposite the hemisphere engaging in slow-wave sleep. Learning tasks, such as those including predator recognition, demonstrated the open eye could be preferential. This has also been shown to be the favored behavior of belugas, although inconsistencies have arisen directly relating the sleeping hemisphere and open eye. Keeping one eye open aids birds in engaging in USWS while mid-flight as well as helping them observe predators in their vicinity. Also crocodilians have been shown to sleep with one eye open. Given that USWS is preserved also in blind animals or during a lack of visual stimuli, it cannot be considered as a consequence of keeping an eye open while sleeping. Furthermore, the open eye in dolphins does not forcibly activate the contralateral hemisphere. Although unilateral vision plays a considerable role in keeping active the contralateral hemisphere, it is not the motive power of USWS. Consequently, USWS might be generated by endogenous mechanisms. === Thermoregulation === Brain temperature has been shown to drop when a sleeping EEG is


id: unihemispheric-slow-wave-sleep-20260505-2
file: data/en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep-2.md
category: reference
title: Unihemispheric slow-wave sleep
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep
date_saved: 2026-05-05T11:04:43.626925+00:00
instance: kb-cron
parent: unihemispheric-slow-wave-sleep-20260505-0
summary:
==== Regulation based on surroundings ==== Birds can sleep more efficiently with both hemispheres sleeping simultaneously (bihemispheric slow-wave sleep) when in safe conditions, but will increase the usage of USWS if they are in a potentially more dangerous environment. It is more beneficial to sleep using both hemispheres; however, the positives of unihemispheric slow-wave sleep prevail over its negatives under extreme conditions. While in unihemispheric slow-wave sleep, birds will sleep with one open eye towards the direction from which predators are more likely to approach. When birds do this in a flock, it's called the "group edge effect". The mallard is one bird that has been used experimentally to illustrate the "group edge effect". Birds positioned at the edge of the flock are most alert, scanning often for predators. These birds are more at risk than the birds in the center of the flock and are required to be on the lookout for both their own safety and the safety of the group as a whole. They have been observed spending more time in unihemispheric slow-wave sleep than the birds in the center. Since USWS allows for the one eye to be open, the cerebral hemisphere that undergoes slow-wave sleep


id: unihemispheric-slow-wave-sleep-20260505-3
file: data/en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep-3.md
category: reference
title: Unihemispheric slow-wave sleep
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Unihemispheric_slow-wave_sleep
date_saved: 2026-05-05T11:04:43.626925+00:00
instance: kb-cron
parent: unihemispheric-slow-wave-sleep-20260505-0
summary:
== Future research == Recent studies have illustrated that the white-crowned sparrow, as well as other passerines, have the capability of sleeping most significantly during the migratory season while in flight. However, the sleep patterns in this study were observed during migratory restlessness in captivity and might not be analogous to those of free-flying birds. Free-flying birds might be able to spend some time sleeping while in non-migratory flight as well when in the unobstructed sky as opposed to in controlled captive conditions. To truly determine if birds can sleep in flight, recordings of brain activity must take place during flight instead of after landing. A method of recording brain activity in pigeons during flight has recently proven promising in that it could obtain an EEG of each hemisphere but for relatively short periods of time. Coupled with simulated wind tunnels in a controlled setting, these new methods of measuring brain activity could elucidate the truth behind whether or not birds sleep during flight. Additionally, based on research elucidating the role of acetylcholine in control of USWS, additional neurotransmitters are being researched to understand their roles in the asymmetric sleep model. == See also == Sleep in animals == References


id: list-of-unsolved-problems-in-physics-20260505-0
file: data/en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics-0.md
category: reference
title: List of unsolved problems in physics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics
date_saved: 2026-05-05T11:04:45.237201+00:00
instance: kb-cron
parent: list-of-unsolved-problems-in-physics-20260505-0
summary:
The following is a list of notable unsolved problems grouped into broad areas of physics. Some of the major unsolved problems in physics are theoretical, meaning that existing theories are currently unable to explain certain observed phenomena or experimental results. Others are experimental, involving challenges in creating experiments to test proposed theories or to investigate specific phenomena in greater detail. A number of important questions remain open in the area of physics beyond the Standard Model, such as the strong CP problem, determining the absolute mass of neutrinos, understanding matter–antimatter asymmetry, and identifying the nature of dark matter and dark energy. Another significant problem lies within the mathematical framework of the Standard Model itself, which remains inconsistent with general relativity. This incompatibility causes both theories to break down under extreme conditions, such as within known spacetime gravitational singularities like those at the Big Bang and at the centers of black holes beyond their event horizons. == Historical problems and lists == Isaac Newton in his book Opticks (first edition 1704), published a list of 31 queries about light. In 1900, Lord Kelvin in a speech identified two main issues in classical physics that represented "two clouds" for the physics of


id: list-of-unsolved-problems-in-physics-20260505-1
file: data/en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics-1.md
category: reference
title: List of unsolved problems in physics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics
date_saved: 2026-05-05T11:04:45.237201+00:00
instance: kb-cron
parent: list-of-unsolved-problems-in-physics-20260505-0
summary:
== Quantum gravity == Quantum gravity: Can quantum mechanics and general relativity be realized as a fully consistent theory (perhaps as a quantum field theory)? Is spacetime fundamentally continuous or discrete? Would a consistent theory involve a force mediated by a hypothetical graviton, or be a product of a discrete structure of spacetime itself (as in loop quantum gravity)? Are there deviations from the predictions of general relativity at very small or very large scales or in other extreme circumstances that flow from a quantum gravity mechanism? Black holes, black hole information paradox, and black hole radiation: Do black holes produce thermal radiation, as expected on theoretical grounds? Does this radiation contain information about their inner structure, as suggested by gauge–gravity duality, or not, as implied by Hawking's original calculation? If not, and black holes can evaporate away, what happens to the information stored in them (since quantum mechanics does not provide for the destruction of information)? Or does the radiation stop at some point, leaving black hole remnants? Is there another way to probe their internal structure somehow, if such a structure even exists? The cosmic censorship hypothesis and the chronology protection conjecture: Can singularities not hidden behind an


id: list-of-unsolved-problems-in-physics-20260505-2
file: data/en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics-2.md
category: reference
title: List of unsolved problems in physics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics
date_saved: 2026-05-05T11:04:45.237201+00:00
instance: kb-cron
parent: list-of-unsolved-problems-in-physics-20260505-0
summary:
Dark matter: What is the identity of dark matter? Is it a particle? If so, is it a WIMP, axion, the lightest superpartner (LSP), or some other particle? Or, are the phenomena attributed to dark matter the result of an alternate theory of gravity separate from general relativity altogether? Despite extensive research, the exact composition of dark matter remains unknown. It is inferred from gravitational effects on visible matter, radiation, and the universe's large-scale structure. Understanding its properties is crucial for a comprehensive understanding of the universe. Dark energy: What is the cause of the observed accelerating expansion of the universe (the de Sitter phase)? Are the observations rightly interpreted as the accelerating expansion of the universe, or are they evidence that the cosmological principle is false? Why is the energy density of the dark energy component of the same magnitude as the density of matter at present when the two evolve quite differently over time; could it be simply that we are observing at exactly the right time? Is dark energy a pure cosmological constant or are models of quintessence such as phantom energy applicable? Dark flow: Is a non-spherically-symmetric gravitational pull from outside the observable universe responsible for


id: list-of-unsolved-problems-in-physics-20260505-3
file: data/en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics-3.md
category: reference
title: List of unsolved problems in physics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics
date_saved: 2026-05-05T11:04:45.237201+00:00
instance: kb-cron
parent: list-of-unsolved-problems-in-physics-20260505-0
summary:
The QCD vacuum: Many of the equations in non-perturbative QCD are currently unsolved. These energies are the energies sufficient for the formation and description of atomic nuclei. How thus does low energy /non-pertubative QCD give rise to the formation of complex nuclei and nuclear constituents? Generations of matter: Why are there three generations of quarks and leptons? Is there a theory that can explain the masses of particular quarks and leptons in particular generations from first principles (a theory of Yukawa couplings)? Neutrino mass: What is the absolute mass of neutrinos? Are they Dirac or Majorana fermions? Is the mass hierarchy normal or inverted? Is the CP violating phase equal to 0? Reactor antineutrino anomaly: There is an anomaly in the existing body of data regarding the antineutrino flux from nuclear reactors around the world. Measured values of this flux appears to be only 94% of the value expected from theory. It is unknown whether this is due to unknown physics (such as sterile neutrinos), experimental error in the measurements, or errors in the theoretical flux calculations. Strong CP problem and axions: Why is the strong nuclear interaction invariant to parity and charge conjugation? Is Peccei–Quinn theory the solution to


id: list-of-unsolved-problems-in-physics-20260505-4
file: data/en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics-4.md
category: reference
title: List of unsolved problems in physics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics
date_saved: 2026-05-05T11:04:45.237201+00:00
instance: kb-cron
parent: list-of-unsolved-problems-in-physics-20260505-0
summary:
Solar cycle: How does the Sun generate its periodically reversing large-scale magnetic field? How do other solar-like stars generate their magnetic fields, and what are the similarities and differences between stellar activity cycles and that of the Sun? What caused the Maunder Minimum and other grand minima, and how does the solar cycle recover from a minima state? Coronal heating problem: Why is the Sun's corona (atmosphere layer) so much hotter than the Sun's surface? Why is the magnetic reconnection effect many orders of magnitude faster than predicted by standard models? Astrophysical jet: Why do only certain accretion discs surrounding certain astronomical objects emit relativistic jets along their polar axes? Why are there quasi-periodic oscillations in many accretion discs? Why does the period of these oscillations scale as the inverse of the mass of the central object? Why are there sometimes overtones, and why do these appear at different frequency ratios in different objects? Diffuse interstellar bands: What is responsible for the numerous interstellar absorption lines detected in astronomical spectra? Are they molecular in origin, and if so which molecules are responsible for them? How do they form? Supermassive black holes: What is the origin of the M–sigma relation between


id: list-of-unsolved-problems-in-physics-20260505-5
file: data/en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics-5.md
category: reference
title: List of unsolved problems in physics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics
date_saved: 2026-05-05T11:04:45.237201+00:00
instance: kb-cron
parent: list-of-unsolved-problems-in-physics-20260505-0
summary:
Quantum chromodynamics: What are the phases of strongly interacting matter, and what roles do they play in the evolution of the cosmos? What is the detailed partonic structure of the nucleons? What does QCD predict for the properties of strongly interacting matter? What determines the key features of QCD, and what is their relation to the nature of gravity and spacetime? Does QCD truly lack CP violations? Quark–gluon plasma: Where is the onset of deconfinement: 1) as a function of temperature and chemical potentials? 2) as a function of relativistic heavy-ion collision energy and system size? What is the mechanism of energy and baryon-number stopping leading to creation of quark-gluon plasma in relativistic heavy-ion collisions? Why is sudden hadronization and the statistical-hadronization model a near-to-perfect description of hadron production from quark–gluon plasma? Is quark flavor conserved in quark–gluon plasma? Are strangeness and charm in chemical equilibrium in quark–gluon plasma? Does strangeness in quark–gluon plasma flow at the same speed as up and down quark flavours? Why does deconfined matter show ideal flow? Specific models of quark–gluon plasma formation: Do gluons saturate when their occupation number is large? Do gluons form a dense system called colour glass condensate? What are the


id: list-of-unsolved-problems-in-physics-20260505-6
file: data/en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics-6.md
category: reference
title: List of unsolved problems in physics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics
date_saved: 2026-05-05T11:04:45.237201+00:00
instance: kb-cron
parent: list-of-unsolved-problems-in-physics-20260505-0
summary:
== Plasma physics == Plasma physics and fusion power: Fusion energy may potentially provide power from an abundant resource (e.g. hydrogen) without the type of radioactive waste that fission energy currently produces. However, can ionized gases (plasma) be confined long enough and at a high enough temperature to create fusion power? What is the physical origin of H-mode? The injection problem: Fermi acceleration is thought to be the primary mechanism that accelerates astrophysical particles to high energy. However, it is unclear what mechanism causes those particles to initially have energies high enough for Fermi acceleration to work on them. Alfvénic turbulence: In the solar wind and the turbulence in solar flares, coronal mass ejections, and magnetospheric substorms are major unsolved problems in space plasma physics. Ball lightning: the exact physical nature of this mystery in atmospheric electricity. == Biophysics == Abiogenesis: can life be created from physical processes alone? Stochasticity and robustness to noise in gene expression: How do genes govern our body, withstanding different external pressures and internal stochasticity? Certain models exist for genetic processes, but we are far from understanding the whole picture, in particular in development where gene expression must be tightly regulated. Quantitative study of the


id: list-of-unsolved-problems-in-physics-20260505-7
file: data/en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics-7.md
category: reference
title: List of unsolved problems in physics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics
date_saved: 2026-05-05T11:04:45.237201+00:00
instance: kb-cron
parent: list-of-unsolved-problems-in-physics-20260505-0
summary:
=== High-energy physics/particle physics === Existence of pentaquarks (1964–2015): In July 2015, the LHCb collaboration at CERN identified pentaquarks in the Λ0b→J/ψK−p channel, which represents the decay of the bottom lambda baryon (Λ0b) into a J/ψ meson (J/ψ), a kaon (K−) and a proton (p). The results showed that sometimes, instead of decaying directly into mesons and baryons, the Λ0b decayed via intermediate pentaquark states. The two states, named P+c(4380) and P+c(4450), had individual statistical significances of 9 σ and 12 σ, respectively, and a combined significance of 15 σ—enough to claim a formal discovery. The two pentaquark states were both observed decaying strongly to J/ψp, hence must have a valence quark content of two up quarks, a down quark, a charm quark, and an anti-charm quark (uudcc), making them charmonium-pentaquarks. Existence of quark-gluon plasma, a new phase of matter was discovered and confirmed in experiments at CERN-SPS (2000), BNL-RHIC (2005) and CERN-LHC (2010). Higgs boson and electroweak symmetry breaking (1963–2012): The mechanism responsible for breaking the electroweak gauge symmetry, giving mass to the W and Z bosons, was solved with the discovery of the Higgs boson of the Standard Model, with the expected couplings to the weak bosons. No


id: accretion-disk-20260505-0
file: data/en.wikipedia.org/wiki/Accretion_disk-0.md
category: reference
title: Accretion disk
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Accretion_disk
date_saved: 2026-05-05T11:04:46.406689+00:00
instance: kb-cron
parent: accretion-disk-20260505-0
summary:
An accretion disk is a structure (often a circumstellar disk) formed by diffuse material in orbital motion around a massive central body. The central body is most frequently a star. Friction, uneven irradiance, magnetohydrodynamic effects, and other forces induce instabilities causing orbiting material in the disk to spiral inward toward the central body. Gravitational and frictional forces compress and raise the temperature of the material, causing the emission of electromagnetic radiation. The frequency range of that radiation depends on the central object's mass. Accretion disks of young stars and protostars radiate in the infrared; those around neutron stars and black holes in the X-ray part of the spectrum. The study of oscillation modes in accretion disks is referred to as diskoseismology. == Manifestations == Accretion disks are a ubiquitous phenomenon in astrophysics; active galactic nuclei, protoplanetary disks, and gamma ray bursts all involve accretion disks. These disks very often give rise to astrophysical jets coming from the vicinity of the central object. Jets are an efficient way for the star-disk system to shed angular momentum without losing too much mass. The most prominent accretion disks are those of active galactic nuclei and of quasars, which are thought to be massive


id: accretion-disk-20260505-1
file: data/en.wikipedia.org/wiki/Accretion_disk-1.md
category: reference
title: Accretion disk
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Accretion_disk
date_saved: 2026-05-05T11:04:46.406689+00:00
instance: kb-cron
parent: accretion-disk-20260505-0
summary:
=== α-Disk model === Shakura and Sunyaev (1973) proposed turbulence in the gas as the source of an increased viscosity. Assuming subsonic turbulence and the disk height as an upper limit for the size of the eddies, the disk viscosity can be estimated as ν = α c s H {\displaystyle \nu =\alpha c_{\rm {s}}H} where c s {\displaystyle c_{\rm {s}}} is the sound speed, H {\displaystyle H} is the scale height of the disk, and α {\displaystyle \alpha } is a free parameter between zero (no accretion) and approximately one. In a turbulent medium ν ≈ v t u r b l t u r b {\displaystyle \nu \approx v_{\rm {turb}}l_{\rm {turb}}} , where v t u r b {\displaystyle v_{\rm {turb}}} is the velocity of turbulent cells relative to the mean gas motion, and l t u r b {\displaystyle l_{\rm {turb}}} is the size of the largest turbulent cells, which is estimated as l t u r b ≈ H = c s / Ω {\displaystyle l_{\rm {turb}}\approx H=c_{\rm {s}}/\Omega } and v t u r b ≈ c s {\displaystyle v_{\rm {turb}}\approx c_{\rm {s}}} , where Ω = ( G M ) 1 / 2 r


id: accretion-disk-20260505-2
file: data/en.wikipedia.org/wiki/Accretion_disk-2.md
category: reference
title: Accretion disk
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Accretion_disk
date_saved: 2026-05-05T11:04:46.406689+00:00
instance: kb-cron
parent: accretion-disk-20260505-0
summary:
Most astrophysical disks do not meet this criterion and are therefore prone to this magnetorotational instability. The magnetic fields present in astrophysical objects (required for the instability to occur) are believed to be generated via dynamo action. === Magnetic fields and jets === Accretion disks are usually assumed to be threaded by the external magnetic fields present in the interstellar medium. These fields are typically weak (about few micro-Gauss), but they can get anchored to the matter in the disk, because of its high electrical conductivity, and carried inward toward the central star. This process can concentrate the magnetic flux around the centre of the disk giving rise to very strong magnetic fields. Formation of powerful astrophysical jets along the rotation axis of accretion disks requires a large scale poloidal magnetic field in the inner regions of the disk. Such magnetic fields may be advected inward from the interstellar medium or generated by a magnetic dynamo within the disk. Magnetic fields strengths at least of order 100 Gauss seem necessary for the magneto-centrifugal mechanism to launch powerful jets. There are problems, however, in carrying external magnetic flux inward toward the central star of the disk. High electric conductivity dictates that


id: accretion-disk-20260505-3
file: data/en.wikipedia.org/wiki/Accretion_disk-3.md
category: reference
title: Accretion disk
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Accretion_disk
date_saved: 2026-05-05T11:04:46.406689+00:00
instance: kb-cron
parent: accretion-disk-20260505-0
summary:
== Decretion disk == The opposite of an accretion disk is an decretion disk where instead of material accreting from a disk on to a central object, material is excreted from the center outward onto the disk. They are formed from matter ejected from a star, and are often assosicated with Be stars. == See also == == Notes == == References == == Further reading == Frank, Juhan; Andrew King; Derek Raine (2002), Accretion power in astrophysics (Third ed.), Cambridge University Press, ISBN 978-0-521-62957-7 Krolik, Julian H. (1999), Active Galactic Nuclei, Princeton University Press, ISBN 978-0-691-01151-6 Blaes, Omer (2014). "General Overview of Black Hole Accretion Theory". Space Science Reviews. 183 (1–4): 21–41. arXiv:1304.4879. Bibcode:2014SSRv..183...21B. doi:10.1007/s11214-013-9985-6. A modern review focused on models for turbulence required by alpha process. Abramowicz, M.A. (December 22, 2005). "Super-Eddington Black Hole Accretion:: Polish Doughnuts and Slim Disks". In Merloni, Andrea; Nayakshin, Sergei; Sunyaev, Rashid A. (eds.). Growing Black Holes: Accretion in a Cosmological Context. Berlin, Heidelberg: Springer Berlin Heidelberg. pp. 257–273. doi:10.1007/11403913_49. ISBN 978-3-540-25275-7. Retrieved 2026-04-13. Review with a good introduction to the topic. == External links == Professor John F. Hawley homepage, University of Virginia (archived 2015) The Dynamical Structure of Nonradiative Black Hole


id: ball-lightning-20260505-0
file: data/en.wikipedia.org/wiki/Ball_lightning-0.md
category: reference
title: Ball lightning
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ball_lightning
date_saved: 2026-05-05T11:04:47.852283+00:00
instance: kb-cron
parent: ball-lightning-20260505-0
summary:
Ball lightning is a rare and unexplained phenomenon described as luminescent spherical objects that vary from pea-sized to several meters in diameter. Though usually associated with thunderstorms, the observed phenomenon is reported to last considerably longer than the split-second flash of a lightning bolt and is distinct from St. Elmo's fire and will-o'-the-wisp. Some 20th-century reports describe balls that eventually explode and leave behind an odor of sulfur. Descriptions of ball lightning appear in a variety of accounts over the centuries and have received attention from scientists. An optical spectrum of what appears to have been a ball lightning event was published in January 2014 and included a video at high frame rate. Nevertheless, scientific data on ball lightning remain scarce. Although laboratory experiments have produced effects that are visually similar to reports of ball lightning, how these relate to the phenomenon remains unclear. == Characteristics == Descriptions of ball lightning vary widely. It has been described as moving up and down, sideways or in unpredictable trajectories, hovering and moving with or against the wind; attracted to, unaffected by, or repelled from buildings, people, cars and other objects. Some accounts describe it as moving through solid masses of wood or


id: ball-lightning-20260505-1
file: data/en.wikipedia.org/wiki/Ball_lightning-1.md
category: reference
title: Ball lightning
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ball_lightning
date_saved: 2026-05-05T11:04:47.852283+00:00
instance: kb-cron
parent: ball-lightning-20260505-0
summary:
=== The sloop Catherine and Mary === In December 1726, a number of British newspapers printed an extract of a letter from John Howell of the sloop Catherine and Mary: As we were coming thro' the Gulf of Florida on 29th of August, a large ball of fire fell from the Element and split our mast in Ten Thousand Pieces, if it were possible; split our Main Beam, also Three Planks of the Side, Under Water, and Three of the Deck; killed one man, another had his Hand carried of [sic], and had it not been for the violent rains, our Sails would have been of a Blast of Fire. === HMS Montague === One particularly large example was reported "on the authority of Dr. Gregory" in 1749: Admiral Chambers on board the HMS Montague, 4 November 1749, was taking an observation just before noon ... he observed a large ball of blue fire about three miles [5 km] distant from them. They immediately lowered their topsails, but it came up so fast upon them, that, before they could raise the main tack, they observed the ball rise almost perpendicularly, and not above forty or fifty yards [35 or 45


id: ball-lightning-20260505-2
file: data/en.wikipedia.org/wiki/Ball_lightning-2.md
category: reference
title: Ball lightning
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ball_lightning
date_saved: 2026-05-05T11:04:47.852283+00:00
instance: kb-cron
parent: ball-lightning-20260505-0
summary:
Once my parents were away, and I was at the all-night vigil with my grandfather in the small church in Alexandria. During the service there was a powerful thunderstorm, streaks of lightning flashed one after the other, and it seemed as if the peals of thunder would shake even the church and the whole world to its foundations. Suddenly it became quite dark, a blast of wind from the open door blew out the flame of the candles which were lit in front of the iconostasis, there was a long clap of thunder, louder than before, and I suddenly saw a fiery ball flying from the window straight towards the head of the Emperor. The ball (it was of lightning) whirled around the floor, then passed the chandelier and flew out through the door into the park. My heart froze, I glanced at my grandfather – his face was completely calm. He crossed himself just as calmly as he had when the fiery ball had flown near us, and I felt that it was unseemly and not courageous to be frightened as I was. I felt that one had only to look at what was happening and believe in the


id: ball-lightning-20260505-3
file: data/en.wikipedia.org/wiki/Ball_lightning-3.md
category: reference
title: Ball lightning
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ball_lightning
date_saved: 2026-05-05T11:04:47.852283+00:00
instance: kb-cron
parent: ball-lightning-20260505-0
summary:
Willy Ley discussed a sighting in Paris on 5 July 1852 "for which sworn statements were filed with the French Academy of Sciences". During a thunderstorm, a tailor living next to Church of the Val-de-Grâce saw a ball the size of a human head come out of the fireplace. It flew around the room, reentered the fireplace, and exploded in and destroyed the top of the chimney. On 30 April 1877, a ball of lightning entered the Golden Temple at Amritsar, India, and exited through a side door. Several people observed the ball, and the incident is inscribed on the front wall of Darshani Deori. On 22 November 1894, an unusually prolonged instance of natural ball lightning occurred in Golden, Colorado, which suggests it could be artificially induced from the atmosphere. The Golden Globe newspaper reported:A beautiful yet strange phenomenon was seen in this city on last Monday night. The wind was high and the air seemed to be full of electricity. In front of, above and around the new Hall of Engineering of the School of Mines, balls of fire played tag for half an hour, to the wonder and amazement of all who saw the display. In this


id: ball-lightning-20260505-4
file: data/en.wikipedia.org/wiki/Ball_lightning-4.md
category: reference
title: Ball lightning
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ball_lightning
date_saved: 2026-05-05T11:04:47.852283+00:00
instance: kb-cron
parent: ball-lightning-20260505-0
summary:
== Direct measurements of natural ball lightning == In January 2014, scientists from Northwest Normal University in Lanzhou, China, published the results of recordings made in July 2012 of the optical spectrum of what was thought to be natural ball lightning made by chance during the study of ordinary cloud–ground lightning on the Tibetan Plateau. At a distance of 900 m (3,000 ft), a total of 1.64 seconds of digital video of the ball lightning and its spectrum was made, from the formation of the ball lightning after the ordinary lightning struck the ground, up to the optical decay of the phenomenon. Additional video was recorded by a high-speed (3000 frames/sec) camera, which captured only the last 0.78 seconds of the event, due to its limited recording capacity. Both cameras were equipped with slitless spectrographs. The researchers detected emission lines of neutral atomic silicon, calcium, iron, nitrogen, and oxygen—in contrast with mainly ionized nitrogen emission lines in the spectrum of the parent lightning. The ball lightning traveled horizontally across the video frame at an average speed equivalent of 8.6 m/s (28 ft/s). It had a diameter of 5 m (16 ft) and covered a distance of about 15 m (49


id: ball-lightning-20260505-5
file: data/en.wikipedia.org/wiki/Ball_lightning-5.md
category: reference
title: Ball lightning
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ball_lightning
date_saved: 2026-05-05T11:04:47.852283+00:00
instance: kb-cron
parent: ball-lightning-20260505-0
summary:
=== Vaporized silicon hypothesis === This hypothesis suggests that ball lightning consists of vaporized silicon burning through oxidation. Lightning striking Earth's soil could vaporize the silica contained within it, and somehow separate the oxygen from the silicon dioxide, turning it into pure silicon vapor. As it cools, the silicon could condense into a floating aerosol, bound by its charge, glowing due to the heat of silicon recombining with oxygen. An experimental investigation of this effect, published in 2007, reported producing "luminous balls with lifetime in the order of seconds" by evaporating pure silicon with an electric arc. Videos and spectrographs of this experiment have been made available. This hypothesis got significant supportive data in 2014, when the first ever recorded spectra of natural ball lightning were published. The theorized forms of silicon storage in soil include nanoparticles of Si, SiO, and SiC. Matthew Francis has dubbed this the "dirt clod hypothesis", in which the spectrum of ball lightning shows that it shares chemistry with soil. === Electrically charged solid-core model === In this model, ball lightning is assumed to have a solid, positively charged core. According to this underlying assumption, the core is surrounded by a thin electron layer with


id: ball-lightning-20260505-6
file: data/en.wikipedia.org/wiki/Ball_lightning-6.md
category: reference
title: Ball lightning
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ball_lightning
date_saved: 2026-05-05T11:04:47.852283+00:00
instance: kb-cron
parent: ball-lightning-20260505-0
summary:
=== Buoyant plasma hypothesis === The declassified Project Condign report concludes that buoyant charged plasma formations similar to ball lightning are formed by novel physical, electrical, and magnetic phenomena, and that these charged plasmas are capable of being transported at enormous speeds under the influence and balance of electrical charges in the atmosphere. These plasmas appear to originate due to more than one set of weather and electrically charged conditions, the scientific rationale for which is incomplete or not fully understood. One suggestion is that meteoroids breaking up in the atmosphere and forming charged plasmas as opposed to burning completely or impacting as meteorites could explain some instances of the phenomena, in addition to other unknown atmospheric events. However, according to Stenhoff, this explanation is considered insufficient to explain the ball lightning phenomenon, and would likely not withstand peer review. === Hallucinations induced by magnetic field === Cooray and Cooray (2008) stated that the features of hallucinations experienced by patients having epileptic seizures in the occipital lobe are similar to the observed features of ball lightning. The study also showed that the rapidly changing magnetic field of a close lightning flash is strong enough to excite the neurons in the


id: ball-lightning-20260505-7
file: data/en.wikipedia.org/wiki/Ball_lightning-7.md
category: reference
title: Ball lightning
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ball_lightning
date_saved: 2026-05-05T11:04:47.852283+00:00
instance: kb-cron
parent: ball-lightning-20260505-0
summary:
Spinning electric dipole hypothesis. A 1976 article by V. G. Endean postulated that ball lightning could be described as an electric field vector spinning in the microwave frequency region. Electrostatic Leyden jar models. Stanley Singer discussed (1971) this type of hypothesis and suggested that the electrical recombination time would be too short for the ball lightning lifetimes often reported. Smirnov proposed (1987) a fractal aerogel hypothesis. M. I. Zelikin proposed (2006) an explanation (with a rigorous mathematical foundation) based on the hypothesis of plasma superconductivity (see also). A. Meessen presented a theory at the 10th International Symposium on Ball Lightning (21–27 June 2010, Kaliningrad, Russia) explaining all known properties of ball lightning in terms of collective oscillations of free electrons. The simplest case corresponds to radial oscillations in a spherical plasma membrane. These oscillations are sustained by parametric amplification, resulting from regular "inhalation" of charged particles that are present at lower densities in the ambient air. Ball lightning vanishes thus by silent extinction when the available density of charged particles is too low, while it disappears with a loud and sometimes very violent explosion when this density is too high. Electronic oscillations are also possible as stationary waves in a


id: baryogenesis-20260505-0
file: data/en.wikipedia.org/wiki/Baryogenesis-0.md
category: reference
title: Baryogenesis
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Baryogenesis
date_saved: 2026-05-05T11:04:49.171800+00:00
instance: kb-cron
parent: baryogenesis-20260505-0
summary:
In physical cosmology, baryogenesis (also known as baryosynthesis) is the physical process that is hypothesized to have taken place during the early universe to produce baryonic asymmetry, the observation that only matter (baryons) and not antimatter (antibaryons) is detected in the universe (other than in cosmic ray collisions). Since it is assumed in cosmology that the particles we see were created using the same physics we measure today, and in particle physics experiments today matter and antimatter are always symmetric, the dominance of matter over antimatter is unexplained. A number of theoretical mechanisms are proposed to account for this discrepancy, namely identifying conditions that favour symmetry breaking and the creation of normal matter (as opposed to antimatter). This imbalance has to be exceptionally small, on the order of 1 in every 1630000000 (≈2×109) particles a small fraction of a second after the Big Bang. After most of the matter and antimatter was annihilated, what remained was all the baryonic matter in the current universe, along with a much greater number of bosons. Experiments reported in 2010 at Fermilab, however, seem to show that this imbalance is much greater than previously assumed. These experiments involved a series of particle collisions and


id: baryogenesis-20260505-1
file: data/en.wikipedia.org/wiki/Baryogenesis-1.md
category: reference
title: Baryogenesis
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Baryogenesis
date_saved: 2026-05-05T11:04:49.171800+00:00
instance: kb-cron
parent: baryogenesis-20260505-0
summary:
== In the Standard Model == The Standard Model can incorporate baryogenesis, though the amount of net baryons (and leptons) thus created may not be sufficient to account for the present baryon asymmetry. There is a required one excess quark per billion quark-antiquark pairs in the early universe in order to provide all the observed matter in the universe. This insufficiency has not yet been explained, theoretically or otherwise. Baryogenesis within the Standard Model requires the electroweak symmetry breaking to be a first-order cosmological phase transition, since otherwise sphalerons wipe out any baryon asymmetry that happened up to the phase transition. Beyond this, the remaining amount of baryon non-conserving interactions is negligible. The phase transition domain wall breaks the P-symmetry spontaneously, allowing for CP-symmetry violating interactions to break C-symmetry on both its sides. Quarks tend to accumulate on the broken phase side of the domain wall, while anti-quarks tend to accumulate on its unbroken phase side. Due to CP-symmetry violating electroweak interactions, some amplitudes involving quarks are not equal to the corresponding amplitudes involving anti-quarks, but rather have opposite phase (see CKM matrix and Kaon); since time reversal takes an amplitude to its complex conjugate, CPT-symmetry is conserved in this


id: baryon-asymmetry-20260505-0
file: data/en.wikipedia.org/wiki/Baryon_asymmetry-0.md
category: reference
title: Baryon asymmetry
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Baryon_asymmetry
date_saved: 2026-05-05T11:04:50.353706+00:00
instance: kb-cron
parent: baryon-asymmetry-20260505-0
summary:
In physical cosmology, the baryon asymmetry problem, also known as the matter asymmetry problem or the matter–antimatter asymmetry problem, is the observed imbalance in baryonic matter and antibaryonic matter in the observable universe. As the two form and behave in nearly identical ways, it is expected that they would have been created in near equal portions by the Big Bang, where in reality matter makes up the vast majority of the universe (including the Earth and humanity). Neither the Standard Model of particle physics nor the theory of general relativity provides a known explanation for why this should be so, and it is a natural assumption that the universe is neutral with all conserved charges. Since this does not seem to have been the case, it is likely some physical laws must have acted differently or did not exist for matter and/or antimatter. Several competing hypotheses exist to explain the imbalance of matter and antimatter that resulted in baryogenesis. However, there is as of yet no consensus theory to explain the phenomenon, which has been described as "one of the great mysteries in physics". == Sakharov conditions == In 1967, Andrei Sakharov proposed a set of three necessary conditions that


id: baryon-asymmetry-20260505-1
file: data/en.wikipedia.org/wiki/Baryon_asymmetry-1.md
category: reference
title: Baryon asymmetry
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Baryon_asymmetry
date_saved: 2026-05-05T11:04:50.353706+00:00
instance: kb-cron
parent: baryon-asymmetry-20260505-0
summary:
=== Regions of the universe where antimatter dominates === Another possible explanation of the apparent baryon asymmetry is that matter and antimatter are essentially separated into different, widely distant regions of the universe. The formation of antimatter galaxies was originally thought to explain the baryon asymmetry, as from a distance, antimatter atoms are indistinguishable from matter atoms; both produce light (photons) in the same way. Along the boundary between matter and antimatter regions, however, annihilation (and the subsequent production of gamma radiation) would be detectable, depending on its distance and the density of matter and antimatter. Such boundaries, if they exist, would likely lie in deep intergalactic space. The density of matter in intergalactic space is reasonably well established at about one atom per cubic meter. Assuming this is a typical density near a boundary, the gamma ray luminosity of the boundary interaction zone can be calculated. No such zones have been detected, but 30 years of research have placed bounds on how far they might be. On the basis of such analyses, it is now deemed unlikely that any region within the observable universe is dominated by antimatter. === Mirror anti-universe === The state of the universe, as it


id: bgs-conjecture-20260505-0
file: data/en.wikipedia.org/wiki/BGS_conjecture-0.md
category: reference
title: BGS conjecture
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/BGS_conjecture
date_saved: 2026-05-05T11:04:51.490503+00:00
instance: kb-cron
parent: bgs-conjecture-20260505-0
summary:
The Bohigas–Giannoni–Schmit (BGS) conjecture also known as the random matrix conjecture) for simple quantum mechanical systems (ergodic with a classical limit) few degrees of freedom holds that spectra of time reversal-invariant systems whose classical analogues are K-systems show the same fluctuation properties as predicted by the GOE (Gaussian orthogonal ensembles). Alternatively, the spectral fluctuation measures of a classically chaotic quantum system coincide with those of the canonical random-matrix ensemble in the same symmetry class (unitary, orthogonal, or symplectic). That is, the Hamiltonian of a microscopic analogue of a classical chaotic system can be modeled by a random matrix from a Gaussian ensemble as the distance of a few spacings between eigenvalues of a chaotic Hamiltonian operator generically statistically correlates with the spacing laws for eigenvalues of large random matrices. A simple example of the unfolded quantum energy levels in a classically chaotic system correlating like that would be Sinai billiards: Energy levels: − ℏ 2 2 m ▽ 2 ψ + V ( x ) ψ = E i ψ {\displaystyle -{\frac {\hbar ^{2}}{2{\mathit {m}}}}\bigtriangledown ^{2}\psi +{\mathit {V}}({\mathit {x}})\psi ={{\mathit {E}}_{\mathit {i}}}\psi } Spectral density: ρ ( x ) = ∑ i δ ( x − E i ) {\displaystyle


id: color-confinement-20260505-0
file: data/en.wikipedia.org/wiki/Color_confinement-0.md
category: reference
title: Color confinement
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Color_confinement
date_saved: 2026-05-05T11:04:52.706223+00:00
instance: kb-cron
parent: color-confinement-20260505-0
summary:
In quantum chromodynamics (QCD), color confinement or infrared slavery, often simply called confinement, is the phenomenon that color-charged particles (such as quarks and gluons) cannot be isolated, and therefore cannot be directly observed in normal conditions below the Hagedorn temperature of approximately 2 terakelvin (corresponding to energies of approximately 130–140 MeV per particle). Quarks and gluons must clump together to form hadrons. The two main types of hadron are the mesons (one quark, one antiquark) and the baryons (often three quarks or antiquarks, though other exotic variants exist). In addition, colorless glueballs formed only of gluons are also consistent with confinement, though difficult to identify experimentally. Quarks and gluons cannot be separated from their parent hadron without producing new hadrons. == Origin == There is not yet an analytic proof of color confinement in any non-abelian gauge theory. The phenomenon can be understood qualitatively by noting that the force-carrying gluons of QCD have color charge, unlike the photons of quantum electrodynamics (QED). Whereas the electric field between electrically charged particles decreases rapidly as those particles are separated, the gluon field between a pair of color charges forms a narrow flux tube (or string) between them. Because of this behavior of


id: cosmic-coincidence-20260505-0
file: data/en.wikipedia.org/wiki/Cosmic_coincidence-0.md
category: reference
title: Cosmic coincidence
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cosmic_coincidence
date_saved: 2026-05-05T11:04:53.889377+00:00
instance: kb-cron
parent: cosmic-coincidence-20260505-0
summary:
In cosmology, the cosmic coincidence is the observation that at the present epoch of the universe's evolution, the energy densities associated with dark matter and dark energy are of the same order of magnitude, leading to their comparable effects on the dynamics of the cosmos. This coincidence is puzzling because these energies have vastly different effects on the universe's expansion—dark matter tends to slow down expansion through gravitational attraction, while dark energy seems to accelerate it. The observed similarity in the magnitudes of these two components' energy densities at this particular epoch in the universe's history raises questions about whether there might be some underlying physical connection or shared origin between dark matter and dark energy. Indeed, some theories attempt to explain this coincidence by proposing that they are different manifestations of the same fundamental force or field. == References == == See also == Fine-tuned universe


id: cuspy-halo-problem-20260505-0
file: data/en.wikipedia.org/wiki/Cuspy_halo_problem-0.md
category: reference
title: Cuspy halo problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cuspy_halo_problem
date_saved: 2026-05-05T11:04:55.069610+00:00
instance: kb-cron
parent: cuspy-halo-problem-20260505-0
summary:
The cuspy halo problem (also known as the core-cusp problem) is a discrepancy between the inferred dark matter density profiles of low-mass galaxies and the density profiles predicted by cosmological N-body simulations. Nearly all simulations form dark matter halos which have "cuspy" dark matter distributions, with density increasing steeply at small radii, while the rotation curves of most observed dwarf galaxies suggest that they have flat central dark matter density profiles ("cores"). Several possible solutions to the core-cusp problem have been proposed. Many recent studies have shown that including baryonic feedback (particularly feedback from supernovae and active galactic nuclei) can "flatten out" the core of a galaxy's dark matter profile, since feedback-driven gas outflows produce a time-varying gravitational potential that transfers energy to the orbits of the collisionless dark matter particles. Other works have shown that the core-cusp problem can be solved outside of the most widely accepted Lambda-Cold Dark Matter paradigm (ΛCDM): simulations with warm or self-interacting dark matter also produce dark matter cores in low-mass galaxies. It is also possible that the distribution of dark matter that minimizes the system energy has a flat central dark matter density profile. == Simulation results == According to W.J.G. de Blok


id: dark-energy-20260505-0
file: data/en.wikipedia.org/wiki/Dark_energy-0.md
category: reference
title: Dark energy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_energy
date_saved: 2026-05-05T11:05:14.683735+00:00
instance: kb-cron
parent: dark-energy-20260505-0
summary:
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on its largest scales. Its primary effect is to drive the accelerating expansion of the universe. It also slows the rate of structure formation. Assuming that the lambda-CDM model of cosmology is correct, dark energy dominates the universe, contributing 68% of the total mass-energy in the present-day observable universe while dark matter and ordinary (baryonic) matter contribute 27% and 5%, respectively, and other components such as neutrinos and photons are nearly negligible. Dark energy's density is very low: 7×10−30 g/cm3 (6×10−10 J/m3 in mass-energy), much lower than the density of ordinary matter or dark matter within galaxies. However, it dominates the universe's mass–energy content because it is uniform across space. The first observational evidence for dark energy's existence came from measurements of supernovae. Type Ia supernovae have constant luminosity, which means they can be used to accurately measure distances. Comparing this distance to the redshift (which measures the speed at which the supernova is receding) shows that the universe's expansion is accelerating. Prior to this observation, scientists thought that the gravitational attraction of matter and energy in the universe would cause the universe's


id: dark-energy-20260505-1
file: data/en.wikipedia.org/wiki/Dark_energy-1.md
category: reference
title: Dark energy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_energy
date_saved: 2026-05-05T11:05:14.683735+00:00
instance: kb-cron
parent: dark-energy-20260505-0
summary:
=== Late-time dark energy === Nearly all inflation models predict that the total (matter+energy) density of the universe should be very close to the critical density. During the 1980s, most cosmological research focused on models with critical density in matter only, usually 95% cold dark matter (CDM) and 5% ordinary matter (baryons). These models were found to be successful at forming realistic galaxies and clusters, but some problems appeared in the late 1980s: in particular, the model required a value for the Hubble constant lower than preferred by observations, and the model under-predicted observations of large-scale galaxy clustering. These difficulties became stronger after the discovery of anisotropy in the cosmic microwave background by the COBE spacecraft in 1992, and several modified CDM models came under active study through the mid-1990s: these included the Lambda-CDM model and a mixed cold/hot dark matter model. The first direct evidence for dark energy came from supernova observations in 1998 of accelerated expansion in Riess et al. and in Perlmutter et al., and the Lambda-CDM model then became the leading model. Soon after, dark energy was supported by independent observations: in 2000, the BOOMERanG and Maxima cosmic microwave background experiments observed the first acoustic peak


id: dark-energy-20260505-2
file: data/en.wikipedia.org/wiki/Dark_energy-2.md
category: reference
title: Dark energy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_energy
date_saved: 2026-05-05T11:05:14.683735+00:00
instance: kb-cron
parent: dark-energy-20260505-0
summary:
High-precision measurements of the expansion of the universe are required to understand how the expansion rate changes over time and space. In general relativity, the evolution of the expansion rate is estimated from the curvature of the universe and the cosmological equation of state (the relationship between temperature, pressure, and combined matter, energy, and vacuum energy density for any region of space). Measuring the equation of state for dark energy is one of the biggest efforts in observational cosmology today. Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model of cosmology" because of its precise agreement with observations. As of 2013, the Lambda-CDM model is consistent with a series of increasingly rigorous cosmological observations, including the Planck spacecraft and the Supernova Legacy Survey (SNLS). First results from the SNLS reveal that the average behavior (i.e., equation of state) of dark energy behaves like Einstein's cosmological constant to a precision of 10%. Recent results from the Hubble Space Telescope Higher-Z Team indicate that dark energy has been present for at least 9 billion years and during the period preceding cosmic acceleration. In March 2025, the Dark Energy


id: dark-energy-20260505-3
file: data/en.wikipedia.org/wiki/Dark_energy-3.md
category: reference
title: Dark energy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_energy
date_saved: 2026-05-05T11:05:14.683735+00:00
instance: kb-cron
parent: dark-energy-20260505-0
summary:
=== Late-time integrated Sachs–Wolfe effect === Accelerated cosmic expansion causes gravitational potential wells and hills to flatten as photons pass through them, producing cold spots and hot spots on the cosmic microwave background aligned with vast supervoids and superclusters. This so-called late-time Integrated Sachs–Wolfe effect (ISW) is a direct signal of dark energy in a flat universe. It was reported at high significance in 2008 by Ho et al. and Giannantonio et al. === Observational Hubble constant data === A new approach to test evidence of dark energy through observational Hubble constant data (OHD), also known as cosmic chronometers, has gained significant attention in recent years. The Hubble constant, H(z), is measured as a function of cosmological redshift. OHD directly tracks the expansion history of the universe by taking passively evolving early-type galaxies as "cosmic chronometers". From this point, this approach provides standard clocks in the universe. The core of this idea is the measurement of the differential age evolution as a function of redshift of these cosmic chronometers. Thus, it provides a direct estimate of the Hubble parameter H ( z ) = − 1 1 + z d z d t ≈ − 1 1 + z Δ


id: dark-energy-20260505-4
file: data/en.wikipedia.org/wiki/Dark_energy-4.md
category: reference
title: Dark energy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_energy
date_saved: 2026-05-05T11:05:14.683735+00:00
instance: kb-cron
parent: dark-energy-20260505-0
summary:
In quintessence models of dark energy, the observed acceleration of the scale factor is caused by the potential energy of a dynamical field, referred to as quintessence field. Quintessence differs from the cosmological constant in that it can vary in space and time. In order for it not to clump and form structure like matter, the field must be very light so that it has a large Compton wavelength. In the simplest scenarios, the quintessence field has a canonical kinetic term, is minimally coupled to gravity, and does not feature higher order operations in its Lagrangian. No evidence of quintessence is yet available, nor has it been ruled out. It generally predicts a slightly slower acceleration of the expansion of the universe than the cosmological constant. Some scientists think that the best evidence for quintessence would come from violations of Einstein's equivalence principle and variation of the fundamental constants in space or time. Scalar fields are predicted by the Standard Model of particle physics and string theory, but an analogous problem to the cosmological constant problem (or the problem of constructing models of cosmological inflation) occurs: renormalization theory predicts that scalar fields should acquire large masses. The coincidence problem asks


id: dark-energy-20260505-5
file: data/en.wikipedia.org/wiki/Dark_energy-5.md
category: reference
title: Dark energy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_energy
date_saved: 2026-05-05T11:05:14.683735+00:00
instance: kb-cron
parent: dark-energy-20260505-0
summary:
=== Observational skepticism === Some alternatives to dark energy, such as inhomogeneous cosmology, aim to explain the observational data by a more refined use of established theories. In this scenario, dark energy does not actually exist, and is merely a measurement artifact. For example, if we are located in an emptier-than-average region of space, the observed cosmic expansion rate could be mistaken for a variation in time, or acceleration. A different approach uses a cosmological extension of the equivalence principle to show how space might appear to be expanding more rapidly in the voids surrounding our local cluster. While weak, such effects considered cumulatively over billions of years could become significant, creating the illusion of cosmic acceleration, and making it appear as if we live in a Hubble bubble. Yet other possibilities are that the accelerated expansion of the universe is an illusion caused by the relative motion of us to the rest of the universe, or that the statistical methods employed were flawed. A laboratory direct detection attempt failed to detect any force associated with dark energy. Observational skepticism explanations of dark energy have generally not gained much traction among cosmologists. For example, a paper that suggested the anisotropy


id: dark-energy-20260505-6
file: data/en.wikipedia.org/wiki/Dark_energy-6.md
category: reference
title: Dark energy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_energy
date_saved: 2026-05-05T11:05:14.683735+00:00
instance: kb-cron
parent: dark-energy-20260505-0
summary:
== Implications for the fate of the universe == Cosmologists estimate that the acceleration began roughly 5 billion years ago. Before that, it is thought that the expansion was decelerating, due to the attractive influence of matter. The density of dark matter in an expanding universe decreases more quickly than dark energy, and eventually the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved, but the density of dark energy is nearly unchanged (it is exactly constant in the case of a cosmological constant). Projections into the future can differ radically for different models of dark energy. For a cosmological constant, or any other model that predicts that the acceleration will continue indefinitely, the ultimate result will be that galaxies outside the Local Group will have a line-of-sight velocity that continually increases with time, eventually far exceeding the speed of light. This is not a violation of special relativity because the notion of "velocity" used here is different from that of velocity in a local inertial frame of reference, which is still constrained to be less than the speed of light for any massive object (see Uses of the proper distance


id: dark-energy-spectroscopic-instrument-20260505-0
file: data/en.wikipedia.org/wiki/Dark_Energy_Spectroscopic_Instrument-0.md
category: reference
title: Dark Energy Spectroscopic Instrument
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_Energy_Spectroscopic_Instrument
date_saved: 2026-05-05T11:05:15.924157+00:00
instance: kb-cron
parent: dark-energy-spectroscopic-instrument-20260505-0
summary:
The Dark Energy Spectroscopic Instrument (DESI) is a scientific research instrument for conducting spectrographic astronomical surveys of distant galaxies. Its main components are a focal plane containing 5,000 fiber-positioning robots, and a bank of spectrographs which are fed by the fibers. The instrument enables an experiment to probe the expansion history of the universe and the mysterious physics of dark energy. The main DESI survey started in May 2021. DESI sits at an elevation of 6,880 feet (2,100 m), where it has been retrofitted onto the Mayall Telescope on top of Kitt Peak in the Sonoran Desert, which is located 55 miles (89 km) from Tucson, Arizona, United States. The instrument is operated by the Lawrence Berkeley National Laboratory under funding from the U.S. Department of Energy's Office of Science. Construction of the instrument was principally funded by the U.S. Department of Energy's Office of Science, and by other numerous sources including the U.S. National Science Foundation, the British Science and Technology Facilities Council, France's Alternative Energies and Atomic Energy Commission, Mexico's National Council of Science and Technology, Spain's Ministry of Science and Innovation, by the Gordon and Betty Moore Foundation, by the Heising-Simons Foundation, and by collaborating institutions worldwide.


id: dark-energy-spectroscopic-instrument-20260505-1
file: data/en.wikipedia.org/wiki/Dark_Energy_Spectroscopic_Instrument-1.md
category: reference
title: Dark Energy Spectroscopic Instrument
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_Energy_Spectroscopic_Instrument
date_saved: 2026-05-05T11:05:15.924157+00:00
instance: kb-cron
parent: dark-energy-spectroscopic-instrument-20260505-0
summary:
== Development == The DESI instrument implements a new highly multiplexed optical spectrograph on the Mayall Telescope. The new optical corrector design creates a very large, 8.0 square degree field of view on the sky, which combined with the new focal plane instrumentation weighs approximately 10 tonnes. The focal plane accommodates 5,000 small robotic fiber positioners on a 10.4 millimeter pitch. The entire focal plane can be reconfigured for the next exposure in less than two minutes while the telescope slews to the next field. The DESI instrument is capable of taking 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm. The DESI project scope included construction, installation, and commissioning of the new wide-field corrector and corrector support structure for the telescope, the focal plane assembly with 5,000 robotic fiber positioners and ten guide/focus/alignment sensors, a 40-meter optical fiber cabling system that brings light from the focal plane to the spectrographs, ten 3-arm spectrographs, an instrument control system, and a data analysis pipeline. The instrument fabrication was managed by the Lawrence Berkeley National Laboratory and oversees operation of the experiment including a 600-person international scientific collaboration. Cost of construction was $56M from the US Department of


id: dark-energy-spectroscopic-instrument-20260505-2
file: data/en.wikipedia.org/wiki/Dark_Energy_Spectroscopic_Instrument-2.md
category: reference
title: Dark Energy Spectroscopic Instrument
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dark_Energy_Spectroscopic_Instrument
date_saved: 2026-05-05T11:05:15.924157+00:00
instance: kb-cron
parent: dark-energy-spectroscopic-instrument-20260505-0
summary:
=== Early data release === On 13 June 2023 the DESI Early Data Release (EDR) was announced. The EDR contains spectra of nearly two million galaxies, quasars and stars. One early result of the EDR was announced in February 2023 and described a mass migration of stars into the Andromeda Galaxy. The EDR also revealed very distant quasars and very metal-poor stars. In 2025, a team led by Ragadeepika Pucha of the University of Arizona and the University of Utah reported in The Astrophysical Journal the discovery of the largest number of dwarf galaxies including 2,800 black holes (300 intermediate-mass black holes and 2,500 active black holes) from the EDR. ==== Possibly evolving dark energy levels ==== From the level of detail able to be observed, the largest 3-D map of the universe at this point has been created (2024). From this precise data, DESI Director Michael Levi stated:We’re also seeing some potentially interesting differences that could indicate that dark energy is evolving over time. Those may or may not go away with more data, so we’re excited to start analyzing our three-year dataset soon. === Data Release 1 (DR1) === Data Release 1 (DR1), published on 19 March 2025,


id: dwarf-galaxy-problem-20260505-0
file: data/en.wikipedia.org/wiki/Dwarf_galaxy_problem-0.md
category: reference
title: Dwarf galaxy problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dwarf_galaxy_problem
date_saved: 2026-05-05T11:05:17.089029+00:00
instance: kb-cron
parent: dwarf-galaxy-problem-20260505-0
summary:
The dwarf galaxy problem, also known as the missing satellites problem, arises from a mismatch between observed dwarf galaxy numbers and collisionless numerical cosmological simulations that predict the evolution of the distribution of matter in the universe. In simulations, dark matter clusters hierarchically, in ever increasing numbers of halo "blobs" as halos' components' sizes become smaller-and-smaller. However, although there seem to be enough observed normal-sized galaxies to match the simulated distribution of dark matter halos of comparable mass, the number of observed dwarf galaxies is orders of magnitude lower than expected from such simulation. Observations from 2024 suggest that this problem may be resolved for the Milky Way, but some simulations show that the problem of observing too few satellites still exists for other galaxies. == Context == For example, around 38 dwarf galaxies have been observed in the Local Group, and only around 11 orbiting the Milky Way, yet dark matter simulations predict that there should be around 500 dwarf satellites for the Milky Way alone. The dwarf galaxy problem still persists, but now there are too many observed instead of too few. Based on current simulations there should be around 220 satellite galaxies in the Milky Way, however


id: dynamo-theory-20260505-0
file: data/en.wikipedia.org/wiki/Dynamo_theory-0.md
category: reference
title: Dynamo theory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dynamo_theory
date_saved: 2026-05-05T11:05:18.320341+00:00
instance: kb-cron
parent: dynamo-theory-20260505-0
summary:
In physics, the dynamo theory proposes a mechanism by which a celestial body such as Earth or a star generates a magnetic field. The dynamo theory describes the process through which a rotating, convecting, and electrically conducting fluid can maintain a magnetic field over astronomical time scales. A dynamo is thought to be the source of the Earth's magnetic field and the magnetic fields of Mercury and the Jovian planets. == History of theory == When William Gilbert published De Magnete in 1600, he concluded that the Earth is magnetic and proposed the first hypothesis for the origin of this magnetism: permanent magnetism such as that found in lodestone. In 1822, André-Marie Ampère proposed that internal currents are responsible for Earth's magnetism. In 1919, Joseph Larmor proposed that a dynamo might be generating the field. However, even after he advanced his hypothesis, some prominent scientists advanced alternative explanations. The Nobel Prize winner Patrick Blackett did a series of experiments looking for a fundamental relation between angular momentum and magnetic moment, but found none. Walter M. Elsasser, considered a "father" of the presently accepted dynamo theory as an explanation of the Earth's magnetism, proposed that this magnetic field resulted from electric


id: dynamo-theory-20260505-1
file: data/en.wikipedia.org/wiki/Dynamo_theory-1.md
category: reference
title: Dynamo theory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dynamo_theory
date_saved: 2026-05-05T11:05:18.320341+00:00
instance: kb-cron
parent: dynamo-theory-20260505-0
summary:
=== Tidal heating supporting a dynamo === Tidal forces between celestial orbiting bodies cause friction that heats up their interiors. This is known as tidal heating, and it helps keep the interior in a liquid state. A liquid interior that can conduct electricity is required to produce a dynamo. Saturn's Enceladus and Jupiter's Io have enough tidal heating to liquify their inner cores, but they may not create a dynamo because they cannot conduct electricity. Mercury, despite its small size, has a magnetic field, because it has a conductive liquid core created by its iron composition and friction resulting from its highly elliptical orbit. It is theorized that the Moon once had a magnetic field, based on evidence from magnetized lunar rocks, due to its short-lived closer distance to Earth creating tidal heating. An orbit and rotation of a planet helps provide a liquid core, and supplements kinetic energy that supports a dynamo action. == Kinematic dynamo theory == In kinematic dynamo theory the velocity field is prescribed, instead of being a dynamic variable: The model makes no provision for the flow distorting in response to the magnetic field. This method cannot provide the time variable behaviour of a fully


id: dynamo-theory-20260505-2
file: data/en.wikipedia.org/wiki/Dynamo_theory-2.md
category: reference
title: Dynamo theory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dynamo_theory
date_saved: 2026-05-05T11:05:18.320341+00:00
instance: kb-cron
parent: dynamo-theory-20260505-0
summary:
The Navier-Stokes equation for conservation of momentum, again in the same approximation, with the magnetic force and gravitation force as the external forces: D u D t = − 1 ρ 0 ∇ p + ν ∇ 2 u + ρ ′ g + 2 Ω × u + Ω × Ω × R + 1 ρ 0 J × B , {\displaystyle {\frac {D\mathbf {u} }{Dt}}=-{\frac {1}{\rho _{0}}}\nabla p+\nu \nabla ^{2}\mathbf {u} +\rho '\mathbf {g} +2{\boldsymbol {\Omega }}\times \mathbf {u} +{\boldsymbol {\Omega }}\times {\boldsymbol {\Omega }}\times \mathbf {R} +{\frac {1}{\rho _{0}}}\mathbf {J} \times \mathbf {B} ~,} where ν {\displaystyle \,\nu \,} is the kinematic viscosity, ρ 0 {\displaystyle \,\rho _{0}\,} is the mean density and ρ ′ {\displaystyle \rho '} is the relative density perturbation that provides buoyancy (for thermal convection ρ ′ = α Δ T {\displaystyle \;\rho '=\alpha \Delta T\;} where α {\displaystyle \,\alpha \,} is coefficient of thermal expansion), Ω {\displaystyle \,\Omega \,} is the rotation rate of the Earth, and J {\displaystyle \,\mathbf {J} \,} is the electric current density. A transport equation, usually of heat (sometimes of light element concentration): ∂ T ∂ t = κ ∇ 2 T + ε {\displaystyle {\frac {\,\partial


id: dynamo-theory-20260505-3
file: data/en.wikipedia.org/wiki/Dynamo_theory-3.md
category: reference
title: Dynamo theory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dynamo_theory
date_saved: 2026-05-05T11:05:18.320341+00:00
instance: kb-cron
parent: dynamo-theory-20260505-0
summary:
=== Order of magnitude of the magnetic field created by Earth's dynamo === The above formula for the rate of conversion of kinetic energy to magnetic energy, is equivalent to a rate of work done by a force of J × B {\displaystyle \;\mathbf {J} \times \mathbf {B} \;} on the outer core matter, whose velocity is u {\displaystyle \mathbf {u} } . This work is the result of non-magnetic forces acting on the fluid. Of those, the gravitational force and the centrifugal force are conservative and therefore have no overall contribution to fluid moving in closed loops. Ekman number (defined above), which is the ratio between the two remaining forces, namely the viscosity and Coriolis force, is very low inside Earth's outer core, because its viscosity is low (1.2–1.5 ×10−2 pascal-second) due to its liquidity. Thus the main time-averaged contribution to the work is from Coriolis force, whose size is − 2 ρ Ω × u , {\displaystyle \;-2\rho \,\mathbf {\Omega } \times \mathbf {u} \;,} though this quantity and J × B {\displaystyle \mathbf {J} \times \mathbf {B} } are related only indirectly and are not in general equal locally (thus they affect each other but not in


id: dynamo-theory-20260505-4
file: data/en.wikipedia.org/wiki/Dynamo_theory-4.md
category: reference
title: Dynamo theory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Dynamo_theory
date_saved: 2026-05-05T11:05:18.320341+00:00
instance: kb-cron
parent: dynamo-theory-20260505-0
summary:
=== Modern modelling === The complexity of dynamo modelling is so great that models of the geodynamo are limited by the current power of supercomputers, particularly because calculating the Ekman and Rayleigh number of the outer core is extremely difficult and requires a vast number of computations. Many improvements have been proposed in dynamo modelling since the self-consistent breakthrough in 1995. One suggestion in studying the complex magnetic field changes is applying spectral methods to simplify computations. Ultimately, until considerable improvements in computer power are made, the methods for computing realistic dynamo models will have to be made more efficient, so making improvements in methods for computing the model is of high importance for the advancement of numerical dynamo modelling. == Notable people == Stanislav I. Braginsky, research geophysicist == See also == Antidynamo theorem Rotating magnetic field Secular variation == References == Demorest, Paul (21 May 2001). "Dynamo Theory and Earth's magnetic Field (term paper)" (PDF). Archived from the original (PDF) on 21 February 2007. Retrieved 14 October 2011. Fitzpatrick, Richard (18 May 2002). "MHD Dynamo Theory". Plasma Physics. University of Texas at Austin. Retrieved 14 October 2011. Merrill, Ronald T.; McElhinny, Michael W.; McFadden, Phillip L. (1996). The


id: emc-effect-20260505-0
file: data/en.wikipedia.org/wiki/EMC_effect-0.md
category: reference
title: EMC effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/EMC_effect
date_saved: 2026-05-05T11:05:19.519599+00:00
instance: kb-cron
parent: emc-effect-20260505-0
summary:
The EMC effect is the surprising observation that the cross section for deep inelastic scattering from an atomic nucleus is different from that of the same number of free protons and neutrons (collectively referred to as nucleons). From this observation, it can be inferred that the quark momentum distributions in nucleons bound inside nuclei are different from those of free nucleons. This effect was first observed in 1983 at CERN by the European Muon Collaboration, hence the name "EMC effect". It was unexpected, since the average binding energy of protons and neutrons inside nuclei is insignificant when compared to the energy transferred in deep inelastic scattering reactions that probe quark distributions. While over 1000 scientific papers have been written on the topic and numerous hypotheses have been proposed, no definitive explanation for the cause of the effect has been confirmed. Determining the origin of the EMC effect is one of the major unsolved problems in the field of nuclear physics. == Background == Protons and neutrons, collectively referred to as nucleons, are the constituents of atomic nuclei, and nuclear matter such as that in neutron stars. Protons and neutrons themselves are composite particles made up of quarks and gluons, a


id: flatness-problem-20260505-0
file: data/en.wikipedia.org/wiki/Flatness_problem-0.md
category: reference
title: Flatness problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Flatness_problem
date_saved: 2026-05-05T11:05:20.654097+00:00
instance: kb-cron
parent: flatness-problem-20260505-0
summary:
The flatness problem (also known as the oldness problem) is a cosmological fine-tuning problem within the Big Bang model of the universe. Measurements find the current universe close to perfectly flat and expansion of the universe increases flatness. Consequently the early universe must have been exceptionally close to flat. In standard cosmology based on the Friedmann equations the density of matter and energy in the universe affects the curvature of space-time, with a very specific critical value being required for a flat universe. The current density of the universe is observed to be very close to this critical value. Since any departure of the total density from the critical value would increase rapidly over cosmic time, the early universe must have had a density even closer to the critical density, departing from it by one part in 1062 or less. This leads cosmologists to question how the initial density came to be so closely fine-tuned to this 'special' value. The problem was first mentioned by Robert Dicke in 1969. The most commonly accepted solution among cosmologists is cosmic inflation, the idea that the universe went through a brief period of extremely rapid expansion in the first fraction of a second


id: flatness-problem-20260505-1
file: data/en.wikipedia.org/wiki/Flatness_problem-1.md
category: reference
title: Flatness problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Flatness_problem
date_saved: 2026-05-05T11:05:20.654097+00:00
instance: kb-cron
parent: flatness-problem-20260505-0
summary:
=== Measurement === The value of Ω at the present time is denoted Ω0. This value can be deduced by measuring the curvature of spacetime (since Ω = 1, or ρ = ρ c {\displaystyle \rho =\rho _{c}} , is defined as the density for which the curvature K = 0). The curvature can be inferred from a number of observations. One such observation is that of anisotropies (that is, variations with direction - see below) in the Cosmic Microwave Background (CMB) radiation. The CMB is electromagnetic radiation which fills the universe, left over from an early stage in its history when it was filled with photons and a hot, dense plasma. This plasma cooled as the universe expanded, and when it cooled enough to form stable atoms it no longer absorbed the photons. The photons present at that stage have been propagating ever since, growing fainter and less energetic as they spread through the ever-expanding universe. The temperature of this radiation is almost the same at all points on the sky, but there is a slight variation (around one part in 100,000) between the temperature received from different directions. The angular scale of these fluctuations - the typical angle


id: flatness-problem-20260505-2
file: data/en.wikipedia.org/wiki/Flatness_problem-2.md
category: reference
title: Flatness problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Flatness_problem
date_saved: 2026-05-05T11:05:20.654097+00:00
instance: kb-cron
parent: flatness-problem-20260505-0
summary:
One solution to the problem is to invoke the anthropic principle, which states that humans should take into account the conditions necessary for them to exist when speculating about causes of the universe's properties. If two types of universe seem equally likely but only one is suitable for the evolution of intelligent life, the anthropic principle suggests that finding ourselves in that universe is no surprise: if the other universe had existed instead, there would be no observers to notice the fact. The principle can be applied to solve the flatness problem in two somewhat different ways. The first (an application of the 'strong anthropic principle') was suggested by C. B. Collins and Stephen Hawking, who in 1973 considered the existence of an infinite number of universes such that every possible combination of initial properties was held by some universe. In such a situation, they argued, only those universes with exactly the correct density for forming galaxies and stars would give rise to intelligent observers such as humans: therefore, the fact that we observe Ω to be so close to 1 would be "simply a reflection of our own existence". An alternative approach, which makes use of the 'weak anthropic


id: flatness-problem-20260505-3
file: data/en.wikipedia.org/wiki/Flatness_problem-3.md
category: reference
title: Flatness problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Flatness_problem
date_saved: 2026-05-05T11:05:20.654097+00:00
instance: kb-cron
parent: flatness-problem-20260505-0
summary:
=== Post inflation === Although inflationary theory is regarded as having had much success, and the evidence for it is compelling, it is not universally accepted: cosmologists recognize that there are still gaps in the theory and are open to the possibility that future observations will disprove it. In particular, in the absence of any firm evidence for what the field driving inflation should be, many different versions of the theory have been proposed. Many of these contain parameters or initial conditions which themselves require fine-tuning in much the way that the early density does without inflation. For these reasons work is still being done on alternative solutions to the flatness problem. These have included non-standard interpretations of the effect of dark energy and gravity, particle production in an oscillating universe, and use of a Bayesian statistical approach to argue that the problem is non-existent. The latter argument, suggested for example by Evrard and Coles, maintains that the idea that Ω being close to 1 is 'unlikely' is based on assumptions about the likely distribution of the parameter which are not necessarily justified. Despite this ongoing work, inflation remains by far the dominant explanation for the flatness problem. The question


id: flyby-anomaly-20260505-0
file: data/en.wikipedia.org/wiki/Flyby_anomaly-0.md
category: reference
title: Flyby anomaly
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Flyby_anomaly
date_saved: 2026-05-05T11:05:21.874414+00:00
instance: kb-cron
parent: flyby-anomaly-20260505-0
summary:
The flyby anomaly is a discrepancy between current scientific models and the actual increase in speed (i.e. increase in kinetic energy) observed during a planetary flyby (usually of Earth) by a spacecraft. In multiple cases, spacecraft have been observed to gain greater speed than scientists had predicted, but thus far no convincing explanation has been found. This anomaly has been observed as shifts in the S-band and X-band Doppler and ranging telemetry. The largest discrepancy noticed during a flyby is tiny: 13.46 mm/s. == Observations == Gravitational assists are valuable techniques for Solar System exploration. Because the success of such flyby maneuvers depends on the exact geometry of the trajectory, the position and velocity of a spacecraft during its encounter with a planet is continually tracked with great precision by earth telemetry, e.g. via the Deep Space Network (DSN). The flyby anomaly was first noticed during a careful inspection of DSN Doppler data shortly after the Earth flyby of the Galileo spacecraft 8 December 1990. While the Doppler residuals (observed minus computed data) were expected to remain flat, the analysis revealed an unexpected 66 mHz shift, which corresponds to a velocity increase of 3.92 mm/s at perigee. Investigations of this


id: flyby-anomaly-20260505-1
file: data/en.wikipedia.org/wiki/Flyby_anomaly-1.md
category: reference
title: Flyby anomaly
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Flyby_anomaly
date_saved: 2026-05-05T11:05:21.874414+00:00
instance: kb-cron
parent: flyby-anomaly-20260505-0
summary:
A postulated consequence of the assumption that the speed of light is isotropic in all frames, and invariant in the method used to measure the velocity of the space probes by means of the Doppler effect. The inconsistent anomalous values measured: positive, null or negative are simply explained relaxing this assumption. During flyby maneuvers the velocity components of the probe in the direction of the observer Vo are derived from the relative displacement df of the radiofrequency f transmitted by the probe, multiplied by the local speed of the light c′ by the Doppler effect: Vo = (df / f) c′. According to the Céspedes-Curé hypothesis, the movement through variable gravitational energy density fields produces slight variations of the refractive index n′ of space and therefore of the speed of light c′ which leads to unaccounted corrections of the Doppler data that are based on an invariant c. This leads to incorrect estimates of the speed or energy change in the flyby maneuver on the Earth's frame of reference. Unaccounted-for transverse Doppler effect, i.e. the redshift of light source with zero radial and non-zero tangential velocity. However, this cannot explain the similar anomaly in the ranging data. A dark-matter halo


id: fractional-quantum-hall-effect-20260505-0
file: data/en.wikipedia.org/wiki/Fractional_quantum_Hall_effect-0.md
category: reference
title: Fractional quantum Hall effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Fractional_quantum_Hall_effect
date_saved: 2026-05-05T11:05:23.122971+00:00
instance: kb-cron
parent: fractional-quantum-hall-effect-20260505-0
summary:
The fractional quantum Hall effect (fractional QHE or FQHE) is the observation of precisely quantized plateaus in the Hall conductance of 2-dimensional (2D) electrons at fractional values of e 2 / h {\displaystyle e^{2}/h} , where e is the electron charge and h is the Planck constant. At the same time, longitudinal resistance drops to zero (for low enough temperatures) as for the integer QHE. It is a property of a collective state in which electrons bind magnetic flux lines to make new quasiparticles, and excitations have a fractional elementary charge and possibly also fractional statistics. The 1998 Nobel Prize in Physics was awarded to Robert Laughlin, Horst Störmer, and Daniel Tsui "for their discovery of a new form of quantum fluid with fractionally charged excitations". The microscopic origin of the FQHE is a major research topic in condensed matter physics. == Descriptions == The fractional quantum Hall effect (FQHE) is a collective behavior in a 2D system of electrons. In particular magnetic fields, the electron gas condenses into a remarkable liquid state, which is very delicate, requiring high quality material with a low carrier concentration, and extremely low temperatures. As in the integer quantum Hall effect, the Hall resistance


id: fractional-quantum-hall-effect-20260505-1
file: data/en.wikipedia.org/wiki/Fractional_quantum_Hall_effect-1.md
category: reference
title: Fractional quantum Hall effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Fractional_quantum_Hall_effect
date_saved: 2026-05-05T11:05:23.122971+00:00
instance: kb-cron
parent: fractional-quantum-hall-effect-20260505-0
summary:
== Evidence for fractionally-charged quasiparticles == Experiments have reported results that specifically support the understanding that there are fractionally-charged quasiparticles in an electron gas under FQHE conditions. In 1995, the fractional charge of Laughlin quasiparticles was measured directly in a quantum antidot electrometer at Stony Brook University, New York. In 1997, two groups of physicists at the Weizmann Institute of Science in Rehovot, Israel, and at the Commissariat à l'énergie atomique laboratory near Paris, detected such quasiparticles carrying an electric current, through measuring quantum shot noise Both of these experiments have been confirmed with certainty. A more recent experiment measures the quasiparticle charge. In 2020, interferometry experiments conducted by two different groups, at Paris and Purdue, were both able to probe and confirm the braiding statistics of Abelian anyons. == Impact == The FQH effect shows the limits of Landau's symmetry breaking theory. Previously it was held that the symmetry breaking theory could explain all the important concepts and properties of forms of matter. According to this view, the only thing to be done was to apply the symmetry breaking theory to all different kinds of phases and phase transitions. From this perspective, the importance of the FQHE discovered by


id: generalized-uncertainty-principle-20260505-0
file: data/en.wikipedia.org/wiki/Generalized_uncertainty_principle-0.md
category: reference
title: Generalized uncertainty principle
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Generalized_uncertainty_principle
date_saved: 2026-05-05T11:05:25.335002+00:00
instance: kb-cron
parent: generalized-uncertainty-principle-20260505-0
summary:
The generalized uncertainty principle (GUP) is a proposed extension of the Heisenberg uncertainty principle that incorporates potential effects of gravitational interactions into quantum mechanical systems. It emerges from several approaches to quantum gravity, including string theory, loop quantum gravity, and quantum geometry, and suggests the existence of a minimum measurable length, typically associated with the Planck scale. A commonly used formulation of the GUP is: Δ x Δ p ≥ ℏ 2 + β Δ p 2 {\displaystyle \Delta x\Delta p\geq {\frac {\hbar }{2}}+\beta \Delta p^{2}} , where Δ x {\displaystyle \Delta x} and Δ p {\displaystyle \Delta p} represent the uncertainties in position and momentum, ℏ {\displaystyle \hbar } is the reduced Planck constant, and β {\displaystyle \beta } is a parameter related to the minimal length scale. This modification implies that position measurements cannot be made with arbitrary precision, as there exists a fundamental lower bound to spatial resolution. The concept is motivated by the expectation that classical notions of spacetime may break down at extremely small scales, such as the Planck length. Several forms of the GUP have been proposed in the literature, varying in mathematical structure and underlying theoretical assumptions, depending on the specific model of


id: glueball-20260505-0
file: data/en.wikipedia.org/wiki/Glueball-0.md
category: reference
title: Glueball
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Glueball
date_saved: 2026-05-05T11:05:26.568035+00:00
instance: kb-cron
parent: glueball-20260505-0
summary:
In particle physics, a glueball (also gluonium, gluon-ball) is a hypothetical composite particle. It consists solely of gluons, without valence quarks. Such a state is possible because gluons carry color charge and experience the strong interaction between themselves. Glueballs are extremely difficult to identify in particle accelerators, because they mix with ordinary meson states. In pure gauge theory, glueballs are the only states of the spectrum and some of them are stable. Theoretical calculations show that glueballs should exist at energy ranges accessible with current collider technology. However, due to the aforementioned difficulty (among others), they have so far not been observed and identified with certainty, although phenomenological calculations have suggested that an experimentally identified glueball candidate, denoted f0(1710), has properties consistent with those expected of a Standard Model glueball. The prediction that glueballs exist is an essential prediction of QCD as part of the Standard Model of particle physics that has not yet been unambiguously confirmed experimentally. Experimental evidence was announced in 2021, by the TOTEM collaboration at the LHC in collaboration with the DØ collaboration at the former Tevatron collider at Fermilab, of odderon (a composite gluonic particle with odd C-parity) exchange. This exchange, associated with a quarkless


id: glueball-20260505-1
file: data/en.wikipedia.org/wiki/Glueball-1.md
category: reference
title: Glueball
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Glueball
date_saved: 2026-05-05T11:05:26.568035+00:00
instance: kb-cron
parent: glueball-20260505-0
summary:
== Lattice QCD simulations == Lattice QCD provides a way to study the glueball spectrum theoretically and from first principles. Some of the first quantities calculated using lattice QCD methods (in 1980) were glueball mass estimates. Morningstar and Peardon computed the masses of the lightest glueballs in QCD without dynamical quarks in 1999. The three lowest states are tabulated below. The presence of dynamical quarks would slightly alter these data, but also makes the computations more difficult. Since that time calculations within QCD (lattice and sum rules) find the lightest glueball to be a scalar with mass in the range of about 1000–1700 MeV/c2. Lattice predictions for scalar and pseudoscalar glueballs, including their excitations, were confirmed by Dyson–Schwinger/Bethe–Salpeter equations in Yang–Mills theory. == Experimental candidates == Particle accelerator experiments are often able to identify unstable composite particles and assign masses to those particles to a precision of approximately 10 MeV/c2, without being able to immediately assign to the particle resonance that is observed all of the properties of that particle. Scores of such particles have been detected, although particles detected in some experiments but not others can be viewed as doubtful. Many of these candidates have been the subject of


id: gravitational-wave-20260505-0
file: data/en.wikipedia.org/wiki/Gravitational_wave-0.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
Gravitational waves are waves of spacetime curvature that propagate at the speed of light and are produced by the relative motion of gravitating masses. They were first predicted by Albert Einstein as a consequence of his general theory of relativity, appearing as "ripples in spacetime curvature". Hundreds of these gravitational waves have since then been observed, first indirectly using binary-pulsar observations and, since 2015, directly through dedicated observatories. Gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation. Newton's law of universal gravitation, part of classical mechanics, does not provide for their existence, instead asserting that gravity has instantaneous effect everywhere. Gravitational waves therefore stand as an important relativistic phenomenon that is absent from Newtonian physics. Gravitational-wave astronomy has the advantage that, unlike electromagnetic radiation, gravitational waves are not affected by intervening matter. Sources that can be studied this way include binary star systems composed of white dwarfs, neutron stars, and black holes; events such as supernovae; and the formation of the early universe shortly after the Big Bang. The first indirect evidence for the existence of gravitational waves came in 1974 from the observed orbital decay of the Hulse–Taylor binary pulsar, which matched


id: gravitational-wave-20260505-1
file: data/en.wikipedia.org/wiki/Gravitational_wave-1.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
The speed of gravitational waves in the general theory of relativity is equal to the speed of light in vacuum, c. Within the theory of special relativity, the constant c is not only about light; instead it is the highest possible speed for any interaction in nature. Formally, c is a conversion factor for changing the unit of time to the unit of space. This makes it the only speed which does not depend either on the motion of an observer or a source of light and/or gravity. Thus, the speed of "light" is also the speed of gravitational waves, and, further, the speed of any massless particle. Such particles include the gluon (carrier of the strong force), the photons that make up light (hence carrier of electromagnetic force), and the hypothetical gravitons (which are the presumptive field particles associated with gravity; however, an understanding of the graviton, if any exist, requires an as-yet unavailable theory of quantum gravity). In August 2017, the LIGO and Virgo detectors received a gravitational wave signal, GW170817, at nearly the same time as gamma ray satellites and optical telescopes received signals from its source in galaxy NGC 4993, about 130 million light years away.


id: gravitational-wave-20260505-2
file: data/en.wikipedia.org/wiki/Gravitational_wave-2.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
The possibility of gravitational waves and that those might travel at the speed of light was discussed in 1893 by Oliver Heaviside, using the analogy between the inverse-square law of gravitation and the electrostatic force. In 1905, Henri Poincaré proposed gravitational waves, emanating from a body and propagating at the speed of light, as being required by the Lorentz transformations and suggested that, in analogy to an accelerating electrical charge producing electromagnetic waves, accelerated masses in a relativistic field theory of gravity should produce gravitational waves. In 1915 Einstein published his general theory of relativity, a complete relativistic theory of gravitation. He conjectured, like Poincaré, that the equation would produce gravitational waves, but, as he mentions in a letter to Schwarzschild in February 1916, these could not be similar to electromagnetic waves. Electromagnetic waves can be produced by dipole motion, requiring both a positive and a negative charge. Gravitation has no equivalent to negative charge. Einstein continued to work through the complexity of the equations of general relativity to find an alternative wave model. The result was published in June 1916, and there he came to the conclusion that the gravitational wave must propagate with the speed of light, and


id: gravitational-wave-20260505-3
file: data/en.wikipedia.org/wiki/Gravitational_wave-3.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
North American Nanohertz Observatory for Gravitational Waves states, that they were created over cosmological time scales by supermassive black holes, identifying the distinctive Hellings-Downs curve in 15 years of radio observations of 67 pulsars. Similar results are published by European Pulsar Timing Array, who claimed a 3 σ {\displaystyle 3\sigma } -significance. They expect that a 5 σ {\displaystyle 5\sigma } -significance will be achieved by 2025 by combining the measurements of several collaborations.


id: gravitational-wave-20260505-4
file: data/en.wikipedia.org/wiki/Gravitational_wave-4.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
== Effects of passing == Gravitational waves are constantly passing Earth; however, even the strongest have a minuscule effect since their sources are generally at a great distance. For example, the waves given off by the cataclysmic final merger of GW150914 reached Earth after travelling over a billion light-years, as a ripple in spacetime that changed the length of a 4 km LIGO arm by a thousandth of the width of a proton, proportionally equivalent to changing the distance to the nearest star outside the Solar System by one hair's width. This tiny effect from even extreme gravitational waves makes them observable on Earth only with the most sophisticated detectors. The effects of a passing gravitational wave, in an extremely exaggerated form, can be visualized by imagining a perfectly flat region of spacetime with a group of motionless test particles lying in a plane, e.g., the surface of a computer screen. As a gravitational wave passes through the particles along a line perpendicular to the plane of the particles, i.e., following the observer's line of vision into the screen, the particles will follow the distortion in spacetime, oscillating in a "cruciform" manner, as shown in the animations. The area enclosed


id: gravitational-wave-20260505-5
file: data/en.wikipedia.org/wiki/Gravitational_wave-5.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
Gravitational waves carry energy away from their sources and, in the case of orbiting bodies, this is associated with an in-spiral or decrease in orbit. Imagine for example a simple system of two masses – such as the Earth–Sun system – moving slowly compared to the speed of light in circular orbits. Assume that these two masses orbit each other in a circular orbit in the x–y plane. To a good approximation, the masses follow simple Keplerian orbits. However, such an orbit represents a changing quadrupole moment. That is, the system will give off gravitational waves. In theory, the loss of energy through gravitational radiation could eventually drop the Earth into the Sun. However, the total energy of the Earth orbiting the Sun (kinetic energy + gravitational potential energy) is about 1.14×1036 joules of which only 200 watts (joules per second) is lost through gravitational radiation, leading to a decay in the orbit by about 1×10−15 meters per day or roughly the diameter of a proton. At this rate, it would take the Earth approximately 3×1013 times more than the current age of the universe to spiral onto the Sun. This estimate overlooks the decrease in r over time, but


id: gravitational-wave-20260505-6
file: data/en.wikipedia.org/wiki/Gravitational_wave-6.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
=== Spinning neutron stars === As noted above, a mass distribution will emit gravitational radiation only when there is spherically asymmetric motion among the masses. A spinning neutron star will generally emit no gravitational radiation because neutron stars are highly dense objects with a strong gravitational field that keeps them almost perfectly spherical. In some cases, however, there might be slight deformities on the surface called "mountains", which are bumps extending no more than 10 centimeters (4 inches) above the surface, that make the spinning spherically asymmetric. This gives the star a quadrupole moment that changes with time, and it will emit gravitational waves until the deformities are smoothed out. === Primordial gravitational wave === Gravitational waves from the early universe could provide a unique probe for cosmology. Because these wave interact very weakly with matter they would propagate freely from very early time when other signals are trapped by the large density of energy. If this gravitational radiation could be detected it would be gravitational wave background complementary to the cosmic microwave background data. However the existence of primordial gravitational waves can also be inferred from their effects. Models of "slow-roll" cosmic inflation in the early universe predicts primordial


id: gravitational-wave-20260505-7
file: data/en.wikipedia.org/wiki/Gravitational_wave-7.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
=== Determining direction of travel === The difficulty in directly detecting gravitational waves means it is also difficult for a single detector to identify by itself the direction of a source. Therefore, multiple detectors are used, both to distinguish signals from other "noise" by confirming the signal is not of earthly origin, and also to determine direction by means of triangulation. This technique uses the fact that the waves travel at the speed of light and will reach different detectors at different times depending on their source direction. Although the differences in arrival time may be just a few milliseconds, this is sufficient to identify the direction of the origin of the wave with considerable precision. Only in the case of GW170814 were three detectors operating at the time of the event, therefore, the direction is precisely defined. The detection by all three instruments led to a very accurate estimate of the position of the source, with a 90% credible region of just 60 deg2, a factor 20 more accurate than before. == Gravitational wave astronomy == During the past century, astronomy has been revolutionized by the use of new methods for observing the universe. Astronomical observations were initially made


id: gravitational-wave-20260505-8
file: data/en.wikipedia.org/wiki/Gravitational_wave-8.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
=== Indirect detection === Although the waves from the Earth–Sun system are minuscule, astronomers can point to other sources for which the radiation should be substantial. One important example is the Hulse–Taylor binary – a pair of stars, one of which is a pulsar. The characteristics of their orbit can be deduced from the Doppler shifting of radio signals given off by the pulsar. Each of the stars is about 1.4 M☉ and the size of their orbits is about 1/75 of the Earth–Sun orbit, just a few times larger than the diameter of our own Sun. The combination of greater masses and smaller separation means that the energy given off by the Hulse–Taylor binary will be far greater than the energy given off by the Earth–Sun system – roughly 1022 times as much. The information about the orbit can be used to predict how much energy (and angular momentum) would be radiated in the form of gravitational waves. As the binary system loses energy, the stars gradually draw closer to each other, and the orbital period decreases. The resulting trajectory of each star is an inspiral, a spiral with decreasing radius. General relativity precisely describes these trajectories; in particular,


id: gravitational-wave-20260505-9
file: data/en.wikipedia.org/wiki/Gravitational_wave-9.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
==== Resonant antennas ==== A simple device theorised to detect the expected wave motion is called a Weber bar – a large, solid bar of metal isolated from outside vibrations. This type of instrument was the first type of gravitational wave detector. Strains in space due to an incident gravitational wave excite the bar's resonant frequency and could thus be amplified to detectable levels. Conceivably, a nearby supernova might be strong enough to be seen without resonant amplification. With this instrument, Joseph Weber claimed to have detected daily signals of gravitational waves. His results, however, were contested in 1974 by physicists Richard Garwin and David Douglass. Modern forms of the Weber bar are still operated, cryogenically cooled, with superconducting quantum interference devices to detect vibration. Weber bars are not sensitive enough to detect anything but extremely powerful gravitational waves. MiniGRAIL is a spherical gravitational wave antenna using this principle. It is based at Leiden University, consisting of an exactingly machined 1,150 kg sphere cryogenically cooled to 20 millikelvins. The spherical configuration allows for equal sensitivity in all directions, and is somewhat experimentally simpler than larger linear devices requiring high vacuum. Events are detected by measuring deformation of the detector sphere.


id: gravitational-wave-20260505-10
file: data/en.wikipedia.org/wiki/Gravitational_wave-10.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
The simplest gravitational waves are those with constant frequency. The waves given off by a spinning, non-axisymmetric neutron star would be approximately monochromatic: a pure tone in acoustics. Unlike signals from supernovae or binary black holes, these signals evolve little in amplitude or frequency over the period it would be observed by ground-based detectors. However, there would be some change in the measured signal, because of Doppler shifting caused by the motion of the Earth. Despite the signals being simple, detection is extremely computationally expensive, because of the long stretches of data that must be analysed. The Einstein@Home project is a distributed computing project similar to SETI@home intended to detect this type of gravitational wave. By taking data from LIGO and GEO, and sending it out in little pieces to thousands of volunteers for parallel analysis on their home computers, Einstein@Home can sift through the data far more quickly than would be possible otherwise. === Space-based interferometers === Space-based interferometers, such as LISA and DECIGO, are also being developed. LISA's design calls for three test masses forming an equilateral triangle, with lasers from each spacecraft to each other spacecraft forming two independent interferometers. LISA is planned to occupy a solar


id: gravitational-wave-20260505-11
file: data/en.wikipedia.org/wiki/Gravitational_wave-11.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
On 11 February 2016, the LIGO collaboration announced the first observation of gravitational waves, from a signal detected at 09:50:45 GMT on 14 September 2015 of two black holes with masses of 29 and 36 solar masses merging about 1.3 billion light-years away. During the final fraction of a second of the merger, it released more than 50 times the power of all the stars in the observable universe combined. The signal increased in frequency from 35 to 250 Hz over 10 cycles (5 orbits) as it rose in strength for a period of 0.2 second. The mass of the new merged black hole was 62 solar masses. Energy equivalent to three solar masses was emitted as gravitational waves. The signal was seen by both LIGO detectors in Livingston and Hanford, with a time difference of 7 milliseconds due to the angle between the two detectors and the source. The signal came from the Southern Celestial Hemisphere, in the rough direction of (but much farther away than) the Magellanic Clouds. The gravitational waves were observed in the region more than 5 sigma (in other words, 99.99997% chances of showing/getting the same result), the probability of finding enough to have been


id: gravitational-wave-20260505-12
file: data/en.wikipedia.org/wiki/Gravitational_wave-12.md
category: reference
title: Gravitational wave
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Gravitational_wave
date_saved: 2026-05-05T11:05:27.833549+00:00
instance: kb-cron
parent: gravitational-wave-20260505-0
summary:
== Bibliography == Berry, Michael V. (1989). Principles of Cosmology and Gravitation. Bristol: A. Hilger. ISBN 978-0-85274-037-8. Collins, Harry (2004). Gravity's Shadow: The Search for Gravitational Waves. Chicago: University of Chicago Press. ISBN 978-0-226-11378-4. Collins, Harry (2017). Gravity's Kiss: The Detection of Gravitational Waves. Cambridge, MA: MIT Press. ISBN 978-0-262-34005-2. Davies, Paul (1980). The Search for Gravity Waves. Cambridge [Eng.]; New York: Cambridge University Press. ISBN 978-0-521-23197-8. Grote, Hartmut (2020). Gravitational Waves: A History of Discovery. Boca Raton; London; New York: CRC Press, Taylor & Francis Group. ISBN 978-0-367-13681-9. Peebles, P. J. E. (1993). Principles of Physical Cosmology. Princeton, N.J: Princeton University Press. ISBN 978-0-691-01933-8. Ciufolini, Ignazio; Wheeler, John Archibald (1995). Gravitation and Inertia. Princeton, N.J: Princeton University Press. ISBN 978-0-691-03323-5. Woolf, Harry, ed. (1980). Some Strangeness in the Proportion. Reading, Mass: Addison-Wesley. ISBN 978-0-201-09924-9. == Further reading == Bartusiak, Marcia (2000). Einstein's Unfinished Symphony: Listening to the Sounds of Space-Time. Washington, DC: Joseph Henry Press. ISBN 978-0-309-06987-8. Chakrabarty, Indrajit (1999). "Gravitational Waves: An Introduction". arXiv:physics/9908041. Landau, L. D.; Lifshit︠s︡, E. M. (1975). The Classical Theory of Fields. Course of Theoretical Physics. Vol. 2. Translated by Hamermesh, Morton. Oxford; New York: Pergamon Press. ISBN 978-0-08-018176-9. Will, Clifford M. (2014). "The


id: greisen-zatsepin-kuzmin-limit-20260505-0
file: data/en.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limit-0.md
category: reference
title: Greisen–Zatsepin–Kuzmin limit
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limit
date_saved: 2026-05-05T11:05:29.078289+00:00
instance: kb-cron
parent: greisen-zatsepin-kuzmin-limit-20260505-0
summary:
The Greisen–Zatsepin–Kuzmin limit (GZK limit or GZK cutoff) is a theoretical upper limit on the energy of cosmic ray protons traveling from other galaxies through the intergalactic medium to our galaxy. The limit is 5×1019 eV (50 EeV), or about 8 joules (the energy of a proton travelling at ≈ 99.99999999999999999998% the speed of light). The limit is set by the slowing effect of interactions of the protons with the microwave background radiation over long distances (≈ 160 million light-years). The limit is at the same order of magnitude as the upper limit for energy at which cosmic rays have experimentally been detected, although indeed some detections appear to have exceeded the limit, as noted below. For example, one extreme-energy cosmic ray, the Oh-My-God Particle, which has been found to possess a record-breaking 3.12×1020 eV (50 joules) of energy (about the same as the kinetic energy of a 95 km/h baseball). In the past, the apparent violation of the GZK limit has inspired cosmologists and theoretical physicists to suggest other ways that circumvent the limit. These theories propose that ultra-high energy cosmic rays are produced near our galaxy or that Lorentz covariance is violated in such a way that protons


id: greisen-zatsepin-kuzmin-limit-20260505-1
file: data/en.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limit-1.md
category: reference
title: Greisen–Zatsepin–Kuzmin limit
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Greisen–Zatsepin–Kuzmin_limit
date_saved: 2026-05-05T11:05:29.078289+00:00
instance: kb-cron
parent: greisen-zatsepin-kuzmin-limit-20260505-0
summary:
== Controversy about cosmic rays above the GZK limit == A suppression of the cosmic-ray flux that can be explained with the GZK limit has been confirmed by the latest generation of cosmic-ray observatories. A former claim by the AGASA experiment that there is no suppression was overruled. It remains controversial whether the suppression is due to the GZK effect. The GZK limit only applies if ultra-high-energy cosmic rays are mostly protons. In July 2007, during the 30th International Cosmic Ray Conference in Mérida, Yucatán, México, the High Resolution Fly's Eye Experiment (HiRes) and the Pierre Auger Observatory (Auger) presented their results on ultra-high-energy cosmic rays (UHECR). HiRes observed a suppression in the UHECR spectrum at just the right energy, observing only 13 events with an energy above the threshold, while expecting 43 with no suppression. This was interpreted as the first observation of the GZK limit. Auger confirmed the flux suppression, but did not claim it to be the GZK limit: instead of the 30 events necessary to confirm the AGASA results, Auger saw only two, which are believed to be heavy-nuclei events. The flux suppression was previously brought into question when the AGASA experiment found no suppression in


id: hessdalen-lights-20260505-0
file: data/en.wikipedia.org/wiki/Hessdalen_lights-0.md
category: reference
title: Hessdalen lights
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hessdalen_lights
date_saved: 2026-05-05T11:05:30.267876+00:00
instance: kb-cron
parent: hessdalen-lights-20260505-0
summary:
The Hessdalen lights are unidentified lights which have been observed in a 12-kilometre-long (7.5 mi) stretch of the Hessdalen valley in rural central Norway periodically since at least the 1930s. == Background == The Hessdalen lights appear both by day and by night, and seem to float through and above the valley. They are usually bright white, yellow or red and can appear above and below the horizon. The duration of the phenomenon may be a few seconds to well over an hour. Sometimes the lights move with enormous speed; at other times they seem to sway slowly back and forth. On yet other occasions, they hover in mid‑air. Unusual lights have been reported in the region since at least the 1930s. Especially high activity occurred between December 1981 and mid-1984, during which the lights were observed 15–20 times per week, attracting many overnight tourists. As of 2010, the number of observations had dwindled, with only 10 to 20 sightings yearly. Since 1983, "Project Hessdalen" initiated by UFO-Norge and UFO-Sverige have attempted to investigate the lights. This project was active as field investigations during 1983–1985. A group of students, engineers, and journalists collaborated as "The Triangle Project" in 1997–1998 and


id: hierarchy-problem-20260505-0
file: data/en.wikipedia.org/wiki/Hierarchy_problem-0.md
category: reference
title: Hierarchy problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hierarchy_problem
date_saved: 2026-05-05T11:05:31.442462+00:00
instance: kb-cron
parent: hierarchy-problem-20260505-0
summary:
In theoretical physics, the hierarchy problem is the problem concerning the large discrepancy between aspects of the weak force and gravity. There is no scientific consensus on why, for example, the weak force is 1024 times stronger than gravity. == Technical definition == A hierarchy problem occurs when the fundamental value of some physical parameter, such as a coupling constant or a mass, in some Lagrangian is vastly different from its effective value, which is the value that gets measured in an experiment. This happens because the effective value is related to the fundamental value by a prescription known as renormalization, which applies corrections to it. Typically the renormalized value of parameters are close to their fundamental values, but in some cases, it appears that there has been a delicate cancellation between the fundamental quantity and the quantum corrections. Hierarchy problems are related to fine-tuning problems and problems of naturalness. Throughout the 2010s, many scientists argued that the hierarchy problem is a specific application of Bayesian statistics. Studying renormalization in hierarchy problems is difficult, because such quantum corrections are usually power-law divergent, which means that the shortest-distance physics are most important. Because we do not know the precise details of


id: hierarchy-problem-20260505-1
file: data/en.wikipedia.org/wiki/Hierarchy_problem-1.md
category: reference
title: Hierarchy problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hierarchy_problem
date_saved: 2026-05-05T11:05:31.442462+00:00
instance: kb-cron
parent: hierarchy-problem-20260505-0
summary:
Δ m H 2 = − | λ f | 2 8 π 2 [ Λ UV 2 + … ] . {\displaystyle \Delta m_{\text{H}}^{2}=-{\frac {|\lambda _{f}|^{2}}{8\pi ^{2}}}[\Lambda _{\text{UV}}^{2}+\dots ].} The Λ UV {\displaystyle \Lambda _{\text{UV}}} is called the ultraviolet cutoff and is the scale up to which the Standard Model is valid. If we take this scale to be the Planck scale, then we have the quadratically diverging Lagrangian. However, suppose there existed two complex scalars (taken to be spin-0) such that λ S = | λ f | 2 {\displaystyle \lambda _{S}=|\lambda _{f}|^{2}} (the couplings to the Higgs are exactly the same). Then by the Feynman rules, the correction (from both scalars) is Δ m H 2 = 2 × λ S 16 π 2 [ Λ UV 2 + … ] . {\displaystyle \Delta m_{\text{H}}^{2}=2\times {\frac {\lambda _{S}}{16\pi ^{2}}}[\Lambda _{\text{UV}}^{2}+\dots ].} (Note that the contribution here is positive. This is because of the spin–statistics theorem, which means that fermions have a negative contribution, and bosons a positive contribution. This fact is exploited.) This gives a total contribution to the Higgs mass to be zero if we include both the fermionic and bosonic particles. Supersymmetry is an extension


id: hierarchy-problem-20260505-2
file: data/en.wikipedia.org/wiki/Hierarchy_problem-2.md
category: reference
title: Hierarchy problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hierarchy_problem
date_saved: 2026-05-05T11:05:31.442462+00:00
instance: kb-cron
parent: hierarchy-problem-20260505-0
summary:
In 1998 Nima Arkani-Hamed, Savas Dimopoulos, and Gia Dvali proposed the ADD model, also known as the model with large extra dimensions, an alternative scenario to explain the weakness of gravity relative to the other forces. This theory requires that the fields of the Standard Model are confined to a four-dimensional membrane, while gravity propagates in several additional spatial dimensions that are large compared to the Planck scale. In 1998–99 Merab Gogberashvili published on arXiv (and subsequently in peer-reviewed journals) a number of articles where he showed that if the Universe is considered as a thin shell (a mathematical synonym for "brane") expanding in 5-dimensional space then it is possible to obtain one scale for particle theory corresponding to the 5-dimensional cosmological constant and Universe thickness, and thus to solve the hierarchy problem. It was also shown that four-dimensionality of the Universe is the result of a stability requirement since the extra component of the Einstein field equations giving the localized solution for matter fields coincides with one of the conditions of stability. Subsequently, there were proposed the closely related Randall–Sundrum scenarios which offered their solution to the hierarchy problem. ==== UV/IR mixing ==== In 2019, a pair of researchers


id: high-temperature-superconductivity-20260505-0
file: data/en.wikipedia.org/wiki/High-temperature_superconductivity-0.md
category: reference
title: High-temperature superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/High-temperature_superconductivity
date_saved: 2026-05-05T11:05:32.684766+00:00
instance: kb-cron
parent: high-temperature-superconductivity-20260505-0
summary:
High-temperature superconductivity (high-Tc or HTS) is superconductivity in materials with a critical temperature (the temperature below which the material behaves as a superconductor) above 77 K (−196.2 °C; −321.1 °F), the boiling point of liquid nitrogen. They are "high-temperature" only relative to previously known superconductors, which function only closer to absolute zero. The first high-temperature superconductor was discovered in 1986 by IBM researchers Georg Bednorz and K. Alex Müller. Although the critical temperature is around 35.1 K (−238.1 °C; −396.5 °F), this material was modified by Ching-Wu Chu to make the first high-temperature superconductor with critical temperature 93 K (−180.2 °C; −292.3 °F). Bednorz and Müller were awarded the Nobel Prize in Physics in 1987 "for their important break-through in the discovery of superconductivity in ceramic materials". Most high-Tc materials are type-II superconductors. The major advantage of high-temperature superconductors is that they can be cooled using liquid nitrogen, in contrast to previously known superconductors, which require expensive and hard-to-handle coolants, primarily liquid helium. A second advantage of high-Tc materials is they retain their superconductivity in higher magnetic fields than previous materials. This is important when constructing superconducting magnets, a primary application of high-Tc materials. The majority of high-temperature superconductors are


id: high-temperature-superconductivity-20260505-1
file: data/en.wikipedia.org/wiki/High-temperature_superconductivity-1.md
category: reference
title: High-temperature superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/High-temperature_superconductivity
date_saved: 2026-05-05T11:05:32.684766+00:00
instance: kb-cron
parent: high-temperature-superconductivity-20260505-0
summary:
Superconductivity was discovered by Kamerlingh Onnes in 1911, in a metal solid. Ever since, researchers have attempted to create superconductivity at higher temperatures with the goal of finding a room-temperature superconductor. By the late 1970s, superconductivity was observed in several metallic compounds (in particular Nb-based, such as NbTi, Nb3Sn, and Nb3Ge) at temperatures that were much higher than those for elemental metals and which could even exceed 20 K (−253.2 °C). In 1986, at the IBM research lab near Zürich in Switzerland, Bednorz and Müller were looking for superconductivity in a new class of ceramics: the copper oxides, or cuprates. In that year, Bednorz and Müller discovered superconductivity in lanthanum barium copper oxide (LBCO), a lanthanum-based cuprate perovskite material, which had a transition temperature of 35 K (Nobel Prize in Physics, 1987). It was soon found that replacing the lanthanum with yttrium (i.e., making YBCO) raised the critical temperature above 90 K. Their results were soon confirmed by many groups. In 1987, Philip W. Anderson gave the first theoretical description of these materials, based on the resonating valence bond (RVB) theory, but a full understanding of these materials is still developing today. These superconductors are now known to possess a


id: high-temperature-superconductivity-20260505-2
file: data/en.wikipedia.org/wiki/High-temperature_superconductivity-2.md
category: reference
title: High-temperature superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/High-temperature_superconductivity
date_saved: 2026-05-05T11:05:32.684766+00:00
instance: kb-cron
parent: high-temperature-superconductivity-20260505-0
summary:
== Properties == The "high-temperature" superconductor class has had many definitions. The label high-Tc should be reserved for materials with critical temperatures greater than the boiling point of liquid nitrogen. However, a number of materials – including the original discovery and recently discovered pnictide superconductors – have critical temperatures below 77 K (−196.2 °C) but nonetheless are commonly referred to in publications as high-Tc class. A substance with a critical temperature above the boiling point of liquid nitrogen, together with a high critical magnetic field and critical current density (above which superconductivity is destroyed), would greatly benefit technological applications. In magnet applications, the high critical magnetic field may prove more valuable than the high Tc itself. Some cuprates have an upper critical field of about 100 tesla. However, cuprate materials are brittle ceramics that are expensive to manufacture and not easily turned into wires or other useful shapes. Furthermore, high-temperature superconductors do not form large, continuous superconducting domains, rather clusters of microdomains within which superconductivity occurs. They are therefore unsuitable for applications requiring actual superconductive currents, such as magnets for magnetic resonance spectrometers. For a solution to this (powders), see HTS wire. There has been considerable debate regarding high-temperature superconductivity


id: high-temperature-superconductivity-20260505-3
file: data/en.wikipedia.org/wiki/High-temperature_superconductivity-3.md
category: reference
title: High-temperature superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/High-temperature_superconductivity
date_saved: 2026-05-05T11:05:32.684766+00:00
instance: kb-cron
parent: high-temperature-superconductivity-20260505-0
summary:
== Production == Liquid nitrogen can be produced relatively cheaply, even on-site. The higher temperatures additionally help to avoid some of the problems that arise at liquid helium temperatures, such as the formation of plugs of frozen air that can block cryogenic lines and cause unanticipated and potentially hazardous pressure buildup. == Ongoing research == The question of how superconductivity arises in high-temperature superconductors is one of the major unsolved problems of theoretical condensed matter physics. The mechanism that causes the electrons in these crystals to form pairs is not known. Despite intensive research and many promising leads, an explanation has so far eluded scientists. One reason for this is that the materials in question are generally very complex, multi-layered crystals (for example, BSCCO), making theoretical modelling difficult. Improving the quality and variety of samples also gives rise to considerable research, both with the aim of improved characterisation of the physical properties of existing compounds, and synthesizing new materials, often with the hope of increasing Tc. Technological research focuses on making HTS materials in sufficient quantities to make their use economically viable as well as in optimizing their properties in relation to applications. LK-99, copper-doped lead-apatite, has also been proposed


id: high-temperature-superconductivity-20260505-4
file: data/en.wikipedia.org/wiki/High-temperature_superconductivity-4.md
category: reference
title: High-temperature superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/High-temperature_superconductivity
date_saved: 2026-05-05T11:05:32.684766+00:00
instance: kb-cron
parent: high-temperature-superconductivity-20260505-0
summary:
==== Qualitative explanation ==== In a superconductor, the flow of electrons cannot be resolved into individual electrons, but instead consists of pairs of bound electrons, called Cooper pairs. In conventional superconductors, these pairs are formed when an electron moving through the material distorts the surrounding crystal lattice, which attracts another electron and forms a bound pair. This is sometimes called the "water bed" effect. Each Cooper pair requires a certain minimum energy to be displaced, and if the thermal fluctuations in the crystal lattice are smaller than this energy the pair can flow without dissipating energy. Electron flow without resistance is superconductivity. In a high-Tc superconductor, the mechanism is extremely similar to a conventional superconductor, except that phonons play virtually no role, replaced by spin-density waves. Just as all known conventional superconductors are strong phonon systems, all known high-Tc superconductors are strong spin-density wave systems, within close vicinity of a magnetic transition to, for example, an antiferromagnet. When an electron moves in a high-Tc superconductor, its spin creates a spin-density wave around it. This spin-density wave in turn causes a nearby electron to fall into the spin depression created by the first electron (water-bed). When the system temperature is lowered,


id: hilbert-s-sixth-problem-20260505-0
file: data/en.wikipedia.org/wiki/Hilbert's_sixth_problem-0.md
category: reference
title: Hilbert's sixth problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hilbert's_sixth_problem
date_saved: 2026-05-05T11:05:33.864738+00:00
instance: kb-cron
parent: hilbert-s-sixth-problem-20260505-0
summary:
Hilbert's sixth problem is to axiomatize those branches of physics in which mathematics is prevalent. It occurs on the widely cited list of Hilbert's problems in mathematics that he presented in the year 1900. Quoted in its common English translation, the explicit statement reads: To treat in the same manner, by means of axioms, those physical sciences in which already today mathematics plays an important part; in the first rank are the theory of probabilities and mechanics. Hilbert gave a further explanation of this problem and its possible specific forms: As to the axioms of the theory of probabilities, it seems to me desirable that their logical investigation should be accompanied by a rigorous and satisfactory development of the method of mean values in mathematical physics, and in particular in the kinetic theory of gases. ... Boltzmann's work on the principles of mechanics suggests the problem of developing mathematically the limiting processes, there merely indicated, which lead from the atomistic view to the laws of motion of continua. == History == David Hilbert himself devoted much of his research to the sixth problem; in particular, he worked in those fields of physics that arose after he stated the problem. In


id: koide-formula-20260505-0
file: data/en.wikipedia.org/wiki/Koide_formula-0.md
category: reference
title: Koide formula
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Koide_formula
date_saved: 2026-05-05T11:05:35.059661+00:00
instance: kb-cron
parent: koide-formula-20260505-0
summary:
The Koide formula is an unexplained empirical equation proposed by Yoshio Koide ([ko.i.de], koe-ee-day) in 1981. It relates the masses of the charged leptons, the electron, muon and tau in the following way: Q = m e + m μ + m τ ( m e + m μ + m τ ) 2 = 2 3 , {\displaystyle Q={\frac {m_{\text{e}}+m_{\mu }+m_{\tau }}{\left({\sqrt {m_{\text{e}}}}+{\sqrt {m_{\mu }}}+{\sqrt {m_{\tau }}}\right)^{2}}}={\frac {2}{3}},} This exact value of 2 3 {\displaystyle {\frac {2}{3}}} is still within experimental bounds as of 2014. Koide's formula was first derived based on a preon model that also predicted values for quarks and CKM angles. However, these other predictions are now ruled out experimentally. Later authors have extended similar relations to neutrinos, quarks, and other families of particles. == Overview == The Koide formula is given as: Q = m e + m μ + m τ ( m e + m μ + m τ ) 2 = 2 3 , {\displaystyle Q={\frac {m_{\text{e}}+m_{\mu }+m_{\tau }}{\left({\sqrt {m_{\text{e}}}}+{\sqrt {m_{\mu }}}+{\sqrt {m_{\tau }}}\right)^{2}}}={\frac {2}{3}},} The masses of the electron, muon, and tau are measured respectively as me = 0.51099895000(15) MeV/c2, mμ = 105.6583755(23) MeV/c2, and mτ = 1776.93(09) MeV/c2; the digits


id: koide-formula-20260505-1
file: data/en.wikipedia.org/wiki/Koide_formula-1.md
category: reference
title: Koide formula
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Koide_formula
date_saved: 2026-05-05T11:05:35.059661+00:00
instance: kb-cron
parent: koide-formula-20260505-0
summary:
== Origins == The original derivation postulates m e i ∝ ( z 0 + z i ) 2 {\displaystyle m_{e_{i}}\propto (z_{0}+z_{i})^{2}} with the conditions z 1 + z 2 + z 3 = 0 {\displaystyle z_{1}+z_{2}+z_{3}=0} 1 3 ( z 1 2 + z 2 2 + z 3 2 ) = z 0 2 {\displaystyle {\tfrac {1}{3}}(z_{1}^{2}+z_{2}^{2}+z_{3}^{2})=z_{0}^{2}} from which the formula follows. Besides, masses for neutrinos and down quarks were postulated to be proportional to z i 2 {\displaystyle z_{i}^{2}} while masses for up quarks were postulated to be ∝ ( z 0 + 2 z i ) 2 . {\displaystyle \propto (z_{0}+2z_{i})^{2}~.} The published model justifies the first condition as part of a symmetry breaking scheme, and the second one as a "flavor charge" for preons in the interaction that causes this symmetry breaking. Note that in matrix form with M = A A † {\displaystyle M=A\ A^{\dagger }} and A = Z 0 + Z {\displaystyle A=Z_{0}+Z} the equations are simply tr ⁡ Z = 0 {\displaystyle \operatorname {tr} Z=0} and tr ⁡ Z 0 2 = tr ⁡ Z 2 . {\displaystyle \operatorname {tr} Z_{0}^{2}=\operatorname {tr} Z^{2}.} == Phase formulation == The formula reduces to


id: koide-formula-20260505-2
file: data/en.wikipedia.org/wiki/Koide_formula-2.md
category: reference
title: Koide formula
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Koide_formula
date_saved: 2026-05-05T11:05:35.059661+00:00
instance: kb-cron
parent: koide-formula-20260505-0
summary:
( 2 x 3 − 6 n x 2 + 3 n 2 x − 3 ) ( 2 x 3 + 6 n x 2 + 3 n 2 x + 3 ) {\displaystyle (2x^{3}-6nx^{2}+3n^{2}x-3)(2x^{3}+6nx^{2}+3n^{2}x+3)} or 4 ( x 3 − 3 n x 2 + 3 2 n 2 x − 3 2 ) ( x 3 + 3 n x 2 + 3 2 n 2 x + 3 2 ) {\displaystyle 4(x^{3}-3nx^{2}+{\tfrac {3}{2}}n^{2}x-{\tfrac {3}{2}})(x^{3}+3nx^{2}+{\tfrac {3}{2}}n^{2}x+{\tfrac {3}{2}})} The elementary symmetric polynomials of the roots must reproduce the corresponding coefficients from the polynomial that they solve, so x 1 + x 2 + x 3 = ± 3 n {\displaystyle x_{1}+x_{2}+x_{3}=\pm 3n} and x 1 x 2 + x 2 x 3 + x 3 x 1 = + 3 2 n 2 . {\displaystyle x_{1}x_{2}+x_{2}x_{3}+x_{3}x_{1}=+{\tfrac {3}{2}}n^{2}.} Taking the ratio of these symmetric polynomials, but squaring the first so we divide out the unknown parameter n , {\displaystyle n,} we get a Koide-type formula: Regardless of the value of n , {\displaystyle n,} the solutions to the cubic equation for x {\displaystyle x} must satisfy 2 ( x 1 x 2 + x 2 x 3 + x


id: list-of-hypothetical-particles-20260505-0
file: data/en.wikipedia.org/wiki/List_of_hypothetical_particles-0.md
category: reference
title: List of hypothetical particles
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_hypothetical_particles
date_saved: 2026-05-05T11:05:36.279943+00:00
instance: kb-cron
parent: list-of-hypothetical-particles-20260505-0
summary:
This is a list of hypothetical particles. Hypothetical particles are proposed subatomic or composite entities arising in theoretical particle physics and cosmology that have not been experimentally confirmed. They are typically introduced to address limitations of the Standard Model, unify fundamental interactions, or explain unresolved observations such as dark matter, neutrino masses, baryon asymmetry, or cosmic inflation. Many are mathematically well defined within quantum field theory or its extensions and serve as mediators or constituents in speculative but testable frameworks beyond the Standard Model. Prominent classes include gauge or symmetry-related particles such as the graviton or graviphoton in quantum gravity and extra-dimensional theories, and supersymmetric partners (e.g., neutralinos or charginos) predicted by supersymmetry. Others address specific phenomena, including hidden-sector bosons such as dark photons or light force carriers proposed to explain nuclear anomalies. Hypothetical particles also encompass predicted bound states (e.g., glueballs), topological objects such as magnetic monopoles, and unconventional statistical entities such as anyons or tachyons. Collectively, they form a central component of theoretical model building, guiding experimental searches for physics beyond currently known particles. == Elementary particles == Some theories predict the existence of additional elementary bosons and fermions that are not found in the Standard Model. ===


id: list-of-particles-20260505-0
file: data/en.wikipedia.org/wiki/List_of_particles-0.md
category: reference
title: List of particles
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_particles
date_saved: 2026-05-05T11:05:37.534299+00:00
instance: kb-cron
parent: list-of-particles-20260505-0
summary:
This is a list of known and hypothesized molecular, atomic, and subatomic particles in particle physics, condensed matter physics and cosmology. == Standard Model elementary particles == Elementary particles are particles with no measurable internal structure; that is, it is unknown whether they are composed of other particles. They are the fundamental objects of quantum field theory. Many families and sub-families of elementary particles exist. Elementary particles are classified according to their spin. Fermions have half-integer spin while bosons have integer spin. All the elementary particles of the Standard Model have been experimentally observed, including the Higgs boson in 2012. Many other hypothetical elementary particles, such as the graviton, have been proposed, but not observed experimentally. Notes: [†] An anti-electron (e+) is conventionally called a "positron". === Fermions === Fermions are one of the two fundamental classes of particles, the other being bosons. Fermion particles are described by Fermi–Dirac statistics and have quantum numbers described by the Pauli exclusion principle. They include the quarks and leptons, as well as any composite particles consisting of an odd number of these, such as all baryons and many atoms and nuclei. Fermions have half-integer spin; for all known elementary fermions this is ⁠1/2⁠ħ.


id: list-of-particles-20260505-1
file: data/en.wikipedia.org/wiki/List_of_particles-1.md
category: reference
title: List of particles
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_particles
date_saved: 2026-05-05T11:05:37.534299+00:00
instance: kb-cron
parent: list-of-particles-20260505-0
summary:
Ordinary mesons are made up of a valence quark and a valence antiquark. Because mesons have integer spin (0 or 1) and are not themselves elementary particles, they are classified as "composite" bosons, although being made of elementary fermions. Examples of mesons include the pion, kaon, and the J/ψ. In quantum hadrodynamics, mesons mediate the residual strong force between nucleons. At one time or another, positive signatures have been reported for all of the following exotic mesons but their existences have yet to be confirmed. A tetraquark consists of two valence quarks and two valence antiquarks; A glueball is a bound state of gluons with no valence quarks; Hybrid mesons consist of one or more valence quark–antiquark pairs and one or more real gluons. === Atomic nuclei === Atomic nuclei typically consist of protons and neutrons, although exotic nuclei may consist of other baryons, such as hypertriton which contains a hyperon. These baryons (protons, neutrons, hyperons, etc.) which comprise the nucleus are called nucleons. Each type of nucleus is called a "nuclide", and each nuclide is defined by the specific number of each type of nucleon. "Isotopes" are nuclides which have the same number of protons but differing numbers of


id: list-of-particles-20260505-2
file: data/en.wikipedia.org/wiki/List_of_particles-2.md
category: reference
title: List of particles
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_particles
date_saved: 2026-05-05T11:05:37.534299+00:00
instance: kb-cron
parent: list-of-particles-20260505-0
summary:
== Auxiliary particles == Virtual particles are mathematical tools used in calculations that exhibits some of the characteristics of an ordinary particle but do not obey the mass-shell relation. These particles are unphysical and unobservable. These include: Ghost particles, like Faddeev–Popov ghosts and Pauli–Villars ghosts Spurions, auxiliary field in a quantum field theory that can be used to parameterize any symmetry Soft photons, photons with energies below detectable in experiment. There are also instantons, field configurations which are a local minimum of the Yang–Mills field equation. Instantons are used in nonperturbative calculations of tunneling rates. Instantons have properties similar to particles, specific examples include: Calorons, finite temperature generalization of instantons. Merons, a field configuration which is a non-self-dual solution of the Yang–Mills field equation. The instanton is believed to be composed of two merons. Sphalerons are a field configuration which is a saddle point of the Yang–Mills field equations. Sphalerons are used in nonperturbative calculations of non-tunneling rates. Renormalons, a possible type of singularity arising when using Borel summation. It is a counterpart of an instanton singularity. == Classification by speed == A bradyon (or tardyon) travels slower than the speed of light in vacuum and has a non-zero, real


id: long-delayed-echo-20260505-0
file: data/en.wikipedia.org/wiki/Long_delayed_echo-0.md
category: reference
title: Long delayed echo
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Long_delayed_echo
date_saved: 2026-05-05T11:05:38.710429+00:00
instance: kb-cron
parent: long-delayed-echo-20260505-0
summary:
Long delayed echoes (LDEs) are radio echoes which return to the sender several seconds after a radio transmission has occurred. Delays of longer than 2.7 seconds are considered LDEs. LDEs are considered anomalous and have a number of proposed scientific origins. == History == These echoes were first observed in 1927 by civil engineer and amateur radio operator Jørgen Hals from his home near Oslo, Norway. Hals had repeatedly observed an unexpected second radio echo with a significant time delay after the primary radio echo ended. Unable to account for this strange phenomenon, he wrote a letter to Norwegian physicist Carl Størmer, explaining the event: At the end of the summer of 1927 I repeatedly heard signals from the Dutch short-wave transmitting station PCJJ at Eindhoven. At the same time as I heard these I also heard echoes. I heard the usual echo which goes round the Earth with an interval of about 1/7 of a second as well as a weaker echo about three seconds after the principal echo had gone. When the principal signal was especially strong, I suppose the amplitude for the last echo three seconds later, lay between 1/10 and 1/20 of the principal signal in


id: m82-x-2-20260505-0
file: data/en.wikipedia.org/wiki/M82_X-2-0.md
category: reference
title: M82 X-2
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/M82_X-2
date_saved: 2026-05-05T11:05:39.882670+00:00
instance: kb-cron
parent: m82-x-2-20260505-0
summary:
M82 X-2 is an X-ray pulsar located in the galaxy Messier 82, approximately 12 million light-years from Earth. It is exceptionally luminous, radiating energy equivalent to approximately ten million Suns. This object is part of a binary system: If the pulsar is of an average size, 1.4 M☉, then its companion is at least 5.2 M☉. On average, the pulsar rotates every 1.37 seconds, and revolves around its more massive companion every 2.5 days. M82 X-2 is an ultraluminous X-ray source (ULX), shining about 100 times brighter than theory suggests something of its mass should be able to. Its brightness is many times higher than the Eddington limit, a basic physics guideline that sets an upper limit on the brightness that an object of a given mass should be able to achieve. Possible explanations for violations of the Eddington limit include geometrical effects arising from the funneling of in-falling material along magnetic field lines. While M82 X-2 was previously known as an X-ray source, it was not until an observation campaign to study the newly discovered supernova SN 2014J in January 2014 that X-2's true nature was uncovered. Scientists looking at data from the NuSTAR spacecraft noticed a pulsing in


id: magnetic-monopole-20260505-0
file: data/en.wikipedia.org/wiki/Magnetic_monopole-0.md
category: reference
title: Magnetic monopole
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Magnetic_monopole
date_saved: 2026-05-05T11:05:41.099153+00:00
instance: kb-cron
parent: magnetic-monopole-20260505-0
summary:
In particle physics, a magnetic monopole is a hypothetical particle that is an isolated magnet with only one magnetic pole (a north pole without a south pole or vice versa). A magnetic monopole would have a net north or south "magnetic charge". Modern interest in the concept stems from particle theories, notably grand unified and superstring theories, which predict their existence. The known elementary particles that have electric charge are electric monopoles. Magnetism in bar magnets and electromagnets is not caused by magnetic monopoles, and indeed, there is no known experimental or observational evidence that magnetic monopoles exist. A magnetic monopole is not necessarily an elementary particle, and models for magnetic monopole production can include (but are not limited to) spin-0 monopoles or spin-1 massive vector mesons. The term "magnetic monopole" only refers to the nature of the particle, rather than a designation for a single particle. Some condensed matter systems contain effective (non-isolated) magnetic monopole quasi-particles, or contain phenomena that are mathematically analogous to magnetic monopoles. == Historical background == === Early science and classical physics === Many early scientists attributed the magnetism of lodestones to two different "magnetic fluids" ("effluvia"), a north-pole fluid at one end and a


id: magnetic-monopole-20260505-1
file: data/en.wikipedia.org/wiki/Magnetic_monopole-1.md
category: reference
title: Magnetic monopole
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Magnetic_monopole
date_saved: 2026-05-05T11:05:41.099153+00:00
instance: kb-cron
parent: magnetic-monopole-20260505-0
summary:
== Maxwell's equations == Maxwell's equations of electromagnetism relate the electric and magnetic fields to each other and to the distribution of electric charge and current. The standard equations provide for electric charge, but they posit zero magnetic charge and current. Except for this constraint, the equations are symmetric under the interchange of the electric and magnetic fields. Maxwell's equations are symmetric when the charge and electric current density are zero everywhere, as in vacuum. Maxwell's equations can also be written in a fully symmetric form if one allows for "magnetic charge" analogous to electric charge. With the inclusion of a variable for the density of magnetic charge, say ρm, there is also a "magnetic current density" variable in the equations, jm. If magnetic charge does not exist – or if it exists but is absent in a region of space – then the new terms in Maxwell's equations are all zero, and the extended equations reduce to the conventional equations of electromagnetism such as ∇ ⋅ B = 0 (where ∇⋅ is the divergence operator and B is the magnetic flux density). === In SI units === In the International System of Quantities used with the SI, there are


id: magnetic-monopole-20260505-2
file: data/en.wikipedia.org/wiki/Magnetic_monopole-2.md
category: reference
title: Magnetic monopole
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Magnetic_monopole
date_saved: 2026-05-05T11:05:41.099153+00:00
instance: kb-cron
parent: magnetic-monopole-20260505-0
summary:
== Dirac's quantization == One of the defining advances in quantum theory was Paul Dirac's work on developing a relativistic quantum electromagnetism. Before his formulation, the presence of electric charge was simply inserted into the equations of quantum mechanics (QM), but in 1931 Dirac showed that a discrete charge is implied by QM. That is to say, we can maintain the form of Maxwell's equations and still have magnetic charges. Consider a system consisting of a single stationary electric monopole (an electron, say) and a single stationary magnetic monopole, which would not exert any forces on each other. Classically, the electromagnetic field surrounding them has a momentum density given by the Poynting vector, and it also has a total angular momentum, which is proportional to the product qeqm, and is independent of the distance between them. Quantum mechanics dictates, however, that angular momentum is quantized as a multiple of ħ, so therefore the product qeqm must also be quantized. This means that if even a single magnetic monopole existed in the universe, and the form of Maxwell's equations is valid, all electric charges would then be quantized. Although it would be possible simply to integrate over all space to find


id: magnetic-monopole-20260505-3
file: data/en.wikipedia.org/wiki/Magnetic_monopole-3.md
category: reference
title: Magnetic monopole
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Magnetic_monopole
date_saved: 2026-05-05T11:05:41.099153+00:00
instance: kb-cron
parent: magnetic-monopole-20260505-0
summary:
So that the phase a charged particle gets when going in a loop is the magnetic flux through the loop. When a small solenoid has a magnetic flux, there are interference fringes for charged particles which go around the solenoid, or around different sides of the solenoid, which reveal its presence. But if all particle charges are integer multiples of e, solenoids with a flux of 2π/e have no interference fringes, because the phase factor for any charged particle is exp(2πi) = 1. Such a solenoid, if thin enough, is quantum-mechanically invisible. If such a solenoid were to carry a flux of 2π/e, when the flux leaked out from one of its ends it would be indistinguishable from a monopole. Dirac's monopole solution in fact describes an infinitesimal line solenoid ending at a point, and the location of the solenoid is the singular part of the solution, the Dirac string. Dirac strings link monopoles and antimonopoles of opposite magnetic charge, although in Dirac's version, the string just goes off to infinity. The string is unobservable, so you can put it anywhere, and by using two coordinate patches, the field in each patch can be made nonsingular by sliding the string


id: magnetic-monopole-20260505-4
file: data/en.wikipedia.org/wiki/Magnetic_monopole-4.md
category: reference
title: Magnetic monopole
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Magnetic_monopole
date_saved: 2026-05-05T11:05:41.099153+00:00
instance: kb-cron
parent: magnetic-monopole-20260505-0
summary:
The holonomy of a gauge field maps loops to elements of the gauge group. Infinitesimal loops are mapped to group elements infinitesimally close to the identity. If you imagine a big sphere in space, you can deform an infinitesimal loop that starts and ends at the north pole as follows: stretch out the loop over the western hemisphere until it becomes a great circle (which still starts and ends at the north pole) then let it shrink back to a little loop while going over the eastern hemisphere. This is called lassoing the sphere. Lassoing is a sequence of loops, so the holonomy maps it to a sequence of group elements, a continuous path in the gauge group. Since the loop at the beginning of the lassoing is the same as the loop at the end, the path in the group is closed. If the group path associated to the lassoing procedure winds around the U(1), the sphere contains magnetic charge. During the lassoing, the holonomy changes by the amount of magnetic flux through the sphere. Since the holonomy at the beginning and at the end is the identity, the total magnetic flux is quantized. The magnetic charge is proportional


id: magnetic-monopole-20260505-5
file: data/en.wikipedia.org/wiki/Magnetic_monopole-5.md
category: reference
title: Magnetic monopole
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Magnetic_monopole
date_saved: 2026-05-05T11:05:41.099153+00:00
instance: kb-cron
parent: magnetic-monopole-20260505-0
summary:
In mathematics, a (classical) gauge field is defined as a connection over a principal G-bundle over spacetime. G is the gauge group, and it acts on each fiber of the bundle separately. A connection on a G-bundle tells you how to glue fibers together at nearby points of M. It starts with a continuous symmetry group G that acts on the fiber F, and then it associates a group element with each infinitesimal path. Group multiplication along any path tells you how to move from one point on the bundle to another, by having the G element associated to a path act on the fiber F. In mathematics, the definition of bundle is designed to emphasize topology, so the notion of connection is added on as an afterthought. In physics, the connection is the fundamental physical object. One of the fundamental observations in the theory of characteristic classes in algebraic topology is that many homotopical structures of nontrivial principal bundles may be expressed as an integral of some polynomial over any connection over it. Note that a connection over a trivial bundle can never give us a nontrivial principal bundle. If spacetime is R 4 {\displaystyle \mathbb {R} ^{4}} the


id: magnetic-monopole-20260505-6
file: data/en.wikipedia.org/wiki/Magnetic_monopole-6.md
category: reference
title: Magnetic monopole
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Magnetic_monopole
date_saved: 2026-05-05T11:05:41.099153+00:00
instance: kb-cron
parent: magnetic-monopole-20260505-0
summary:
== Grand unified theories == In more recent years, a new class of theories has also suggested the existence of magnetic monopoles. During the early 1970s, the successes of quantum field theory and gauge theory in the development of electroweak theory and the mathematics of the strong nuclear force led many theorists to move on to attempt to combine them in a single theory known as a Grand Unified Theory (GUT). Several GUTs were proposed, most of which implied the presence of a real magnetic monopole particle. More accurately, GUTs predicted a range of particles known as dyons, of which the most basic state was a monopole. The charge on magnetic monopoles predicted by GUTs is either 1 or 2 gD, depending on the theory. The majority of particles appearing in any quantum field theory are unstable, and they decay into other particles in a variety of reactions that must satisfy various conservation laws. Stable particles are stable because there are no lighter particles into which they can decay and still satisfy the conservation laws. For instance, the electron has a lepton number of one and an electric charge of one, and there are no lighter particles that conserve these


id: magnetic-monopole-20260505-7
file: data/en.wikipedia.org/wiki/Magnetic_monopole-7.md
category: reference
title: Magnetic monopole
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Magnetic_monopole
date_saved: 2026-05-05T11:05:41.099153+00:00
instance: kb-cron
parent: magnetic-monopole-20260505-0
summary:
== Searches for magnetic monopoles == Experimental searches for magnetic monopoles can be placed in one of two categories: those that try to detect preexisting magnetic monopoles and those that try to create and detect new magnetic monopoles. Passing a magnetic monopole through a coil of wire induces a net current in the coil. This is not the case for a magnetic dipole or higher order magnetic pole, for which the net induced current is zero, and hence the effect can be used as an unambiguous test for the presence of magnetic monopoles. In a wire with finite resistance, the induced current quickly dissipates its energy as heat, but in a superconducting loop the induced current is long-lived. By using a highly sensitive "superconducting quantum interference device" (SQUID) one can, in principle, detect even a single magnetic monopole. According to standard inflationary cosmology, magnetic monopoles produced before inflation would have been diluted to an extremely low density today. Magnetic monopoles may also have been produced thermally after inflation, during the period of reheating. However, the current bounds on the reheating temperature span 18 orders of magnitude and as a consequence the density of magnetic monopoles today is not well constrained


id: magnetic-monopole-20260505-8
file: data/en.wikipedia.org/wiki/Magnetic_monopole-8.md
category: reference
title: Magnetic monopole
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Magnetic_monopole
date_saved: 2026-05-05T11:05:41.099153+00:00
instance: kb-cron
parent: magnetic-monopole-20260505-0
summary:
== "Monopoles" in condensed-matter systems == Since around 2003, various condensed-matter physics groups have used the term "magnetic monopole" to describe a different and largely unrelated phenomenon. A true magnetic monopole would be a new elementary particle, and would violate Gauss's law for magnetism ∇⋅B = 0. A monopole of this kind, which would help to explain the law of charge quantization as formulated by Paul Dirac in 1931, has never been observed in experiments. The monopoles studied by condensed-matter groups have none of these properties. They are not a new elementary particle, but rather are an emergent phenomenon in systems of everyday particles (protons, neutrons, electrons, photons); in other words, they are quasi-particles. They are not sources for the B-field (i.e., they do not violate ∇⋅B = 0); instead, they are sources for other fields, for example the H-field, the "B*-field" (related to superfluid vorticity), or various other quantum fields. They are not directly relevant to grand unified theories or other aspects of particle physics, and do not help explain charge quantization—except insofar as studies of analogous situations can help confirm that the mathematical analyses involved are sound. There are a number of examples in condensed-matter physics where collective


id: mass-in-general-relativity-20260505-0
file: data/en.wikipedia.org/wiki/Mass_in_general_relativity-0.md
category: reference
title: Mass in general relativity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mass_in_general_relativity
date_saved: 2026-05-05T11:05:42.338004+00:00
instance: kb-cron
parent: mass-in-general-relativity-20260505-0
summary:
In general relativity, the notion of mass is more subtle than in classical mechanics or special relativity. The theory itself does not single out a preferred local definition of mass, and several distinct notions of mass have been introduced that are applicable under different geometric or physical circumstances. This subtlety stems from the fact that the energy and momentum of the gravitational field cannot be unambiguously localized. As a consequence, mass in general relativity cannot be defined as a local quantity in the same sense as in Newtonian physics, since there is no invariant local energy density for the gravitational field. Instead, notions of mass are recovered indirectly from global or boundary data, which typically requires additional geometric structure, such as symmetries or assumptions about the asymptotic behavior of spacetime. Well-defined notions of total mass exist in important classes of spacetimes, such as asymptotically flat spacetimes and asymptotically anti-de Sitter spacetimes, where suitable boundary conditions allow for a meaningful definition. Other settings require different or more refined constructions. == Conceptual obstacles == In special relativity, the rest mass of a particle can be defined unambiguously in terms of its energy and momentum (see Mass in special relativity). In general relativity,


id: mass-in-general-relativity-20260505-1
file: data/en.wikipedia.org/wiki/Mass_in_general_relativity-1.md
category: reference
title: Mass in general relativity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mass_in_general_relativity
date_saved: 2026-05-05T11:05:42.338004+00:00
instance: kb-cron
parent: mass-in-general-relativity-20260505-0
summary:
g μ ν = η μ ν + h μ ν , {\displaystyle g_{\mu \nu }=\eta _{\mu \nu }+h_{\mu \nu },} where η μ ν {\displaystyle \eta _{\mu \nu }} is the flat Minkowski metric and h μ ν {\displaystyle h_{\mu \nu }} represents deviations that decay suitably at infinity. These expressions provide a coordinate realization of the Hamiltonian definitions given above. In this formulation, the ADM energy E A D M = P 0 {\displaystyle E_{\mathrm {ADM} }=P^{0}} is given by the flux integral P 0 = 1 16 π G ∫ ( ∂ k h j k − ∂ j h k k ) d 2 S j , {\displaystyle P^{0}={\frac {1}{16\pi G}}\int \left(\partial ^{k}h_{jk}-\partial ^{j}h_{kk}\right)d^{2}S_{j},} where S {\displaystyle S} is a large sphere at spatial infinity, S j {\displaystyle S_{j}} denotes its outward-pointing unit normal, and the Einstein summation convention is assumed over spatial indices. Ordinary derivatives appear in this expression because the metric is assumed to approach the flat metric asymptotically. Some intuition for this formula can be obtained by considering spherical surfaces of large radius r {\displaystyle r} . At large distances from the sources, the components of h i j {\displaystyle h_{ij}} typically decay


id: mass-in-general-relativity-20260505-2
file: data/en.wikipedia.org/wiki/Mass_in_general_relativity-2.md
category: reference
title: Mass in general relativity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mass_in_general_relativity
date_saved: 2026-05-05T11:05:42.338004+00:00
instance: kb-cron
parent: mass-in-general-relativity-20260505-0
summary:
== Quasi-local quantities == A limitation of the mass definitions discussed above is that they are defined only at null or spatial infinity and therefore require information about the spacetime geometry arbitrarily far from the gravitating system. In realistic physical situations, such global information is generally unavailable, making such notions of mass difficult to interpret or measure without access to the entire system or a large portion of it. This has motivated the search for notions of mass that can be associated with a finite region of spacetime. Since the 1970s, physicists and mathematicians have therefore pursued the more ambitious goal of defining suitable quasi-local quantities. A quasi-local mass is intended to measure the mass or energy contained within a region enclosed by a closed surface, using only geometric and physical data defined on or inside that surface. The term “quasi-local” reflects the fact that, while such quantities depend on a finite region rather than asymptotic infinity, they cannot be strictly local, since general relativity does not admit a well-defined local energy density for the gravitational field. A wide variety of quasi-local mass and energy definitions have been proposed, including the Hawking energy, the Geroch energy, the Bartnik mass, the


id: mass-in-general-relativity-20260505-3
file: data/en.wikipedia.org/wiki/Mass_in_general_relativity-3.md
category: reference
title: Mass in general relativity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mass_in_general_relativity
date_saved: 2026-05-05T11:05:42.338004+00:00
instance: kb-cron
parent: mass-in-general-relativity-20260505-0
summary:
== References == Ashtekar, Abhay; Magnon-Ashtekar, Anne (1979). "On conserved quantities in general relativity". Journal of Mathematical Physics. 20 (5). AIP Publishing: 793–800. Bibcode:1979JMP....20..793A. doi:10.1063/1.524151. ISSN 0022-2488. Komar, Arthur (1959). "Covariant Conservation Laws in General Relativity". Phys. Rev. 113 (3): 934–936. Bibcode:1959PhRv..113..934K. doi:10.1103/PhysRev.113.934. Arnowitt, R.; Deser, S.; Misner, C. W. (1960-03-15). "Canonical Variables for General Relativity" (PDF). Physical Review. 117 (6). American Physical Society (APS): 1595–1602. Bibcode:1960PhRv..117.1595A. doi:10.1103/physrev.117.1595. ISSN 0031-899X. S2CID 120715041. Arnowitt, Richard; Deser, Stanley; Misner, Charles W. (1962). "The dynamics of general relativity". In Witten, L. (ed.). Gravitation: An Introduction to Current Research. Wiley. pp. 227–265. Bondi, H.; Van Der Burg, M. G. J.; Metzner, A. W. K. (1962-08-21). "Gravitational waves in general relativity, VII. Waves from axi-symmetric isolated system". Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences. 269 (1336). The Royal Society: 21–52. Bibcode:1962RSPSA.269...21B. doi:10.1098/rspa.1962.0161. ISSN 2053-9169. S2CID 120125096. Held (1980). General Relativity and Gravitation, One Hundred Years After the Birth of Einstein, Vol 2. Plenum Press. ISBN 978-0-306-40266-1. Szabados, László B. (2004). "Quasi-Local Energy-Momentum and Angular Momentum in GR". Living Rev. Relativ. 7 (1): 4. Bibcode:2004LRR.....7....4S. doi:10.12942/lrr-2004-4. PMC 5255888. PMID 28179865. Townsend, P. K. (1997). "Black Holes (Lecture notes)". arXiv:gr-qc/9707012. Wald,


id: measure-problem-cosmology-20260505-0
file: data/en.wikipedia.org/wiki/Measure_problem_(cosmology)-0.md
category: reference
title: Measure problem (cosmology)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Measure_problem_(cosmology)
date_saved: 2026-05-05T11:05:43.583664+00:00
instance: kb-cron
parent: measure-problem-cosmology-20260505-0
summary:
The measure problem in cosmology concerns how to compute the ratios of universes of different types within a multiverse. It typically arises in the context of eternal inflation. The problem arises because different approaches to calculating these ratios yield different results, and it is not clear which approach (if any) is correct. Measures can be evaluated by whether they predict observed physical constants, as well as whether they avoid counterintuitive implications, such as the youngness paradox or Boltzmann brains. While dozens of measures have been proposed, few physicists consider the problem to be solved. == The problem == Infinite multiverse theories are becoming increasingly popular, but because they involve infinitely many instances of different types of universes, it is unclear how to compute the fractions of each type of universe. Alan Guth put it this way: In a single universe, cows born with two heads are rarer than cows born with one head. [But in an infinitely branching multiverse] there are an infinite number of one-headed cows and an infinite number of two-headed cows. What happens to the ratio? Sean M. Carroll offered another informal example: Say there are an infinite number of universes in which George W. Bush became


id: measure-problem-cosmology-20260505-1
file: data/en.wikipedia.org/wiki/Measure_problem_(cosmology)-1.md
category: reference
title: Measure problem (cosmology)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Measure_problem_(cosmology)
date_saved: 2026-05-05T11:05:43.583664+00:00
instance: kb-cron
parent: measure-problem-cosmology-20260505-0
summary:
=== Scale-factor cutoff === Time can be parameterized in different ways than proper time. One choice is to parameterize by the scale factor of space a {\displaystyle a} , or more commonly by η ∼ log ⁡ a {\displaystyle \eta \sim \log a} . Then a given region of space expands as e 3 Δ η {\displaystyle e^{3\Delta \eta }} , independent of H {\displaystyle H} . This approach can be generalized to a family of measures in which a small region grows as e 3 H β Δ t β {\displaystyle e^{3H^{\beta }\Delta t_{\beta }}} for some β {\displaystyle \beta } and time-slicing approach t β {\displaystyle t_{\beta }} . Any choice for β {\displaystyle \beta } remains stationary for large times. The scale-factor cutoff measure takes β = 0 {\displaystyle \beta =0} , which avoids the youngness paradox by not giving greater weight to regions that retain high energy density for long periods. This measure is very sensitive to the choice of β {\displaystyle \beta } because any β > 0 {\displaystyle \beta >0} yields the youngness paradox, while any β < 0 {\displaystyle \beta <0} yields an "oldness paradox" in which most life is predicted to exist


id: michigan-spin-physics-center-20260505-0
file: data/en.wikipedia.org/wiki/Michigan_Spin_Physics_Center-0.md
category: reference
title: Michigan Spin Physics Center
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Michigan_Spin_Physics_Center
date_saved: 2026-05-05T11:05:44.773056+00:00
instance: kb-cron
parent: michigan-spin-physics-center-20260505-0
summary:
The University of Michigan Spin Physics Center focuses on studies of spin effects in high polarized proton-proton elastic and inelastic scattering. These polarized scattering experiments use the world-class solid and jet polarized proton targets, which are developed, upgraded and tested at the center. The Center obtained a record density of about 1012 spin-polarized hydrogen atoms per cm3. The center also led the development of the world's first accelerated polarized beams at the 12 GeV Argonne ZGS (in 1973) and then at the 28 GeV Brookhaven AGS. The Center led pioneering experiments at the IUCF Cooler Ring from 1988 until its 2003 shutdown, which developed and tested Siberian snakes and Spin-flippers, which are now used to accelerate, store and use high energy polarized proton beams. The center also leads the International SPIN Collaboration and its proton polarization know-how is used in many experiments worldwide. == Main discoveries == In 1978 the Center found that protons with parallel spins interact much stronger than protons with anti-parallel spin. According to Quantum Chromodynamics the interaction between parallel and anti-parallel spinning proton beams should be the same. Sheldon Glashow called this effect "the thorn in the side of QCD". This effect remained unexplained until today.


id: modified-newtonian-dynamics-20260505-0
file: data/en.wikipedia.org/wiki/Modified_Newtonian_dynamics-0.md
category: reference
title: Modified Newtonian dynamics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
date_saved: 2026-05-05T11:05:46.022752+00:00
instance: kb-cron
parent: modified-newtonian-dynamics-20260505-0
summary:
Modified Newtonian dynamics (MOND) is a theory that proposes a modification of Newton's laws to account for observed properties of galaxies. Modifying Newton's law of gravity results in modified gravity, while modifying Newton's second law results in modified inertia. The latter has received little attention compared to the modified gravity version. Its primary motivation is to explain galaxy rotation curves without invoking dark matter, and is one of the most well-known theories of this class. MOND was developed in 1982 and presented in 1983 by Israeli physicist Mordehai Milgrom. Milgrom noted that galaxy rotation curve data, which seemed to show that galaxies contain more matter than is observed, could also be explained if the gravitational force experienced by a star in the outer regions of a galaxy decays more slowly than predicted by Newton's law of gravity. MOND modifies Newton's laws for extremely small accelerations, which are common in galaxies and galaxy clusters. This provides a good fit to galaxy rotation curve data while leaving the dynamics of the Solar System with its strong gravitational field intact. However, the theory predicts that the gravitational field of the galaxy could influence the orbits of Kuiper Belt objects through the external field


id: modified-newtonian-dynamics-20260505-1
file: data/en.wikipedia.org/wiki/Modified_Newtonian_dynamics-1.md
category: reference
title: Modified Newtonian dynamics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
date_saved: 2026-05-05T11:05:46.022752+00:00
instance: kb-cron
parent: modified-newtonian-dynamics-20260505-0
summary:
Modified inertia: One possibility is to treat it as a modification to Newton's second law, so that the force on an object is not proportional to the particle's acceleration a but rather to μ ( a a 0 ) a . {\textstyle \mu \left({\frac {a}{a_{0}}}\right)a.} In this case, the modified dynamics would apply not only to gravitational phenomena, but also those generated by other forces, for example electromagnetism. This interpretation is experimentally disfavoured by laboratory experiments. Modified gravity: Alternatively, Milgrom's law can be viewed as modifying Newton's universal law of gravity instead, so that the true gravitational force on an object of mass m due to another of mass M is roughly of the form G M m ν ( a 0 a ) r 2 . {\textstyle {\frac {GMm}{\nu \left({\frac {a_{0}}{a}}\right)r^{2}}}.} In this interpretation, Milgrom's modification would apply exclusively to gravitational phenomena. This interpretation has received more attention between the two. Milgrom's law states that for accelerations smaller than a0 accelerations increasingly depart from the standard M · G / r 2 Newtonian relationship of mass and distance, wherein gravitational strength is linearly proportional to mass and the inverse square of distance. Instead, the theory holds that the gravitational


id: modified-newtonian-dynamics-20260505-2
file: data/en.wikipedia.org/wiki/Modified_Newtonian_dynamics-2.md
category: reference
title: Modified Newtonian dynamics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
date_saved: 2026-05-05T11:05:46.022752+00:00
instance: kb-cron
parent: modified-newtonian-dynamics-20260505-0
summary:
a e x < a i n < a 0 {\displaystyle a_{\mathrm {ex} }<a_{\mathrm {in} }<a_{0}} : Deep-MOND regime a i n < a 0 < a e x {\displaystyle a_{\mathrm {in} }<a_{0}<a_{\mathrm {ex} }} : The external field is dominant and the behavior of the system is Newtonian. a i n < a e x < a 0 {\displaystyle a_{\mathrm {in} }<a_{\mathrm {ex} }<a_{0}} : The external field is larger than the internal acceleration of the system, but both are smaller than the critical value. In this case, dynamics is Newtonian but the effective value of G is enhanced by a factor of a0/aex. The external field effect implies a fundamental break with the strong equivalence principle (but not the weak equivalence principle which is required by the Lagrangian). The effect was postulated by Milgrom in the first of his 1983 papers to explain why some open clusters were observed to have no mass discrepancy even though their internal accelerations were below a0. It has since come to be recognized as a crucial element of the MOND paradigm. The dependence in MOND of the internal dynamics of a system on its external environment (in principle, the rest of the


id: modified-newtonian-dynamics-20260505-3
file: data/en.wikipedia.org/wiki/Modified_Newtonian_dynamics-3.md
category: reference
title: Modified Newtonian dynamics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
date_saved: 2026-05-05T11:05:46.022752+00:00
instance: kb-cron
parent: modified-newtonian-dynamics-20260505-0
summary:
Since this Lagrangian does not explicitly depend on time and is invariant under spatial translations this means energy and momentum are conserved according to Noether's theorem. Varying over r yields m a = m g {\displaystyle ma=mg} showing that the weak equivalence principle always applies in QUMOND. However, since ϕ {\displaystyle \phi } and ϕ N {\displaystyle \phi _{N}} are not identical and are non-linearly related this means that the strong equivalence principle must be violated. This can be observed by measuring the external field effect. Furthermore, by varying over ϕ {\displaystyle \phi } we get the following Newton-Poisson equation familiar from Newtonian gravity but now with a subscript to denote that in QUMOND this equation determines the auxiliary gravitational field ϕ N {\displaystyle \phi _{N}} : ∇ 2 ϕ N = 4 π G ρ . {\displaystyle \nabla ^{2}\phi _{N}=4\pi G\rho .} Finally by varying the QUMOND Lagrangian with respect to ϕ N {\displaystyle \phi _{N}} we get the QUMOND field equation: ∇ 2 ϕ = ∇ ⋅ [ ν ( a 0 ‖ ∇ ϕ N ‖ ) ∇ ϕ N ] {\displaystyle \nabla ^{2}\phi =\nabla \cdot \left[\nu \left({\frac {a_{0}}{\left\|\nabla \phi _{N}\right\|}}\right)\nabla \phi _{N}\right]} These two field equations


id: modified-newtonian-dynamics-20260505-4
file: data/en.wikipedia.org/wiki/Modified_Newtonian_dynamics-4.md
category: reference
title: Modified Newtonian dynamics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
date_saved: 2026-05-05T11:05:46.022752+00:00
instance: kb-cron
parent: modified-newtonian-dynamics-20260505-0
summary:
=== Dwarf galaxies === Recent work has shown that many of the dwarf galaxies around the Milky Way and Andromeda are located preferentially in a single plane and have correlated motions. This suggests that they may have formed during a close encounter with another galaxy and hence are tidal dwarf galaxies. If so, the presence of mass discrepancies in these systems constitutes evidence for MOND. In addition, it has been claimed that a gravitational force stronger than Newton's (such as Milgrom's) is required for these galaxies to retain their orbits over time. Centaurus A has a similar plane of dwarf galaxies around it which is challenging for LCDM which expects uniform halos of dwarf galaxies. In MOND, all isolated gravitationally bound objects with a < a0 that are in equilibrium – regardless of their origin – should exhibit a mass discrepancy when analyzed using Newtonian mechanics, and should lie on the BTFR. Under the dark matter hypothesis, objects formed from baryonic material ejected during the merger or tidal interaction of two galaxies ("tidal dwarf galaxies") are expected to be devoid of dark matter and hence show no mass discrepancy. Three objects unambiguously identified as tidal dwarf galaxies appear to have


id: modified-newtonian-dynamics-20260505-5
file: data/en.wikipedia.org/wiki/Modified_Newtonian_dynamics-5.md
category: reference
title: Modified Newtonian dynamics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
date_saved: 2026-05-05T11:05:46.022752+00:00
instance: kb-cron
parent: modified-newtonian-dynamics-20260505-0
summary:
==== Solar System ==== Almost the entire Solar System has gravitational field strengths many orders of magnitude higher than a0 so the increase in gravity due to MOND is negligible. However solar system tests are extremely precise and most observations have proven difficult for MOND to explain. Notably data from lunar laser ranging rules out the simple interpolation function. Radio tracking data of the Cassini spacecraft towards Saturn rules out both the simple and standard interpolation functions by testing an anomalous quadrupole effect predicted by MOND. It is also possible that a full fit of solar system ephemerides where the masses of planets and asteroids are allowed to vary can accommodate this anomalous quadrupole effect since these are currently determined using general relativity only. Observations of long period comets also seem to conflict with higher order predictions of MOND. Furthermore, laboratory experiments of Newton's second law seem to have ruled out modified inertia versions of MOND with experimental accelerations reaching as low as 0.1% of a0 without deviation from the Newtonian expectation. Some solar system observations could support MOND as it has been suggested that the orbits of Kuiper Belt objects are best explained through MOND's external field effect, rather


id: modified-newtonian-dynamics-20260505-6
file: data/en.wikipedia.org/wiki/Modified_Newtonian_dynamics-6.md
category: reference
title: Modified Newtonian dynamics
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
date_saved: 2026-05-05T11:05:46.022752+00:00
instance: kb-cron
parent: modified-newtonian-dynamics-20260505-0
summary:
==== Cosmology ==== It has been claimed that MOND is generally unsuited to forming the basis of cosmology. A significant piece of evidence in favor of standard dark matter is the observed anisotropies in the cosmic microwave background. While ΛCDM is able to explain the observed angular power spectrum, MOND has a much harder time. It is possible to construct relativistic generalizations of MOND that can fit CMB observations, but it requires terms that do not look natural, and several observations (such as the amount of gravitational lensing) are still difficult to explain. MOND also encounters difficulties explaining structure formation, with density perturbations in MOND perhaps growing so rapidly that too much structure is formed by the present epoch. However, galaxy surveys appear to show massive galaxy formation occurring at much greater rapidity early in time than is possible according to ΛCDM. There is a potential link between MOND and cosmology. It has been noted that the value of a0 is within an order of magnitude of cH0, where c is the speed of light and H0 is the Hubble constant (a measure of the present-day expansion rate of the universe). It is also close to the acceleration rate of


id: mpemba-effect-20260505-0
file: data/en.wikipedia.org/wiki/Mpemba_effect-0.md
category: reference
title: Mpemba effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mpemba_effect
date_saved: 2026-05-05T11:05:47.274258+00:00
instance: kb-cron
parent: mpemba-effect-20260505-0
summary:
The Mpemba effect is the observation that very hot liquids or colloids (such as ice cream) can freeze more quickly than colder ones, for similar volumes and surrounding conditions. Physicists remain divided on the effect's reproducibility, precise definition, and underlying mechanisms. It is named after Erasto Mpemba, a Tanzanian teenager who studied it scientifically in the 1960s for the first time, along with Denis Osborne. The Mpemba effect was initially observed in only ice cream and water, and later in other colloids. It has been studied extensively in water, with mixed results, and some experiments finding no reproducible effect. It has also been studied in magnetic alloys, nanomechanical systems, and quantum systems. == Definition == The definition of the Mpemba effect used in theoretical studies varies, making it difficult to compare experiments. Monwhea Jeng proposed this definition for the effect in water: "There exists a set of initial parameters, and a pair of temperatures, such that given two bodies of water identical in these parameters, and differing only in initial uniform temperatures, the hot one will freeze sooner." Even this definition does not specify whether "freezing" refers to the point at which a visible surface layer of ice has formed,


id: mpemba-effect-20260505-1
file: data/en.wikipedia.org/wiki/Mpemba_effect-1.md
category: reference
title: Mpemba effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mpemba_effect
date_saved: 2026-05-05T11:05:47.274258+00:00
instance: kb-cron
parent: mpemba-effect-20260505-0
summary:
=== Studies of the effect in water === Modern studies using freezers with well-understood properties have observed the Mpemba effect where water supercools before freezing. Water that starts out cooler tends to reach a lower supercooled temperature before freezing. Some studies measure the time it takes for a sample to begin to freeze (the start of recalescence, the moment where the heat of freezing first starts to be released) the time it takes to completely freeze, or the difference: the time from the onset of recalescence to the completion of freezing. Some also measure the time it takes for a sample to reach the freezing point of the fluid, before any freezing has begun. In 1995, David Auerbach studied glass beakers placed into a liquid cooling bath, where the water supercooled to −6 to −18 °C (21 to 0 °F; 267 to 255 K) before freezing. In some cases water which started off hotter began freezing first. Considerable random variation was observed in the time required for spontaneous freezing to start, and Auerbach observed the Mpemba effect more frequently when the ambient temperature was between −6 and −12 °C (21 and 10 °F). James Brownridge later studied a variety of


id: mpemba-effect-20260505-2
file: data/en.wikipedia.org/wiki/Mpemba_effect-2.md
category: reference
title: Mpemba effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mpemba_effect
date_saved: 2026-05-05T11:05:47.274258+00:00
instance: kb-cron
parent: mpemba-effect-20260505-0
summary:
== Theoretical explanations == While the definition of the Mpemba effect used in theoretical studies varies, several explanations have been offered for its occurrence. In 2017, two research groups independently and simultaneously found a theoretical Mpemba effect and also predicted a new "inverse" Mpemba effect in which heating a cooled, far-from-equilibrium system takes less time than another system that is initially closer to equilibrium. Zhiyue Lu and Oren Raz yielded a general criterion based on Markovian statistical mechanics, predicting the appearance of the inverse Mpemba effect in the Ising model and diffusion dynamics. Antonio Lasanta and co-authors also predicted the direct and inverse Mpemba effects for a granular gas in a far-from-equilibrium initial state. Lasanta's paper also suggested that a very generic mechanism leading to both Mpemba effects is due to a particle velocity distribution function that significantly deviates from the Maxwell–Boltzmann distribution. In 2024, building on Kumar's work, Isha Malhotra simulated single colloids placed in a different, double-well potential, and predicted conditions under which two specific ranges of hotter starting temperatures lead to faster freezing, but not temperatures in between those ranges. Supercooling is a component of many theoretical explanations, particularly the tendency of hot liquids that are cooled


id: mpemba-effect-20260505-3
file: data/en.wikipedia.org/wiki/Mpemba_effect-3.md
category: reference
title: Mpemba effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mpemba_effect
date_saved: 2026-05-05T11:05:47.274258+00:00
instance: kb-cron
parent: mpemba-effect-20260505-0
summary:
"Heat questions". HyperPhysics. Georgia State University. "Mpemba effect: Why hot water can freeze faster than cold". A possible explanation of the Mpemba Effect Tyrovolas, Ilias J. (2019). "New Explanation for the Mpemba Effect". The 5th International Electronic Conference on Entropy and Its Applications. p. 2. doi:10.3390/ecea-5-06658. "The Mpemba effect: Hot Water may Freeze Faster than Cold Water". An analysis of the Mpemba effect London South Bank University "The Mpemba Effect". Archived from the original on 9 October 2011. – History and analysis of the Mpemba effect "The story of the Mpemba effect told by the protagonists". YouTube. 10 January 2013. Archived from the original on 12 December 2021. An historical interview with Erasto B. Mpemba, Dr Denis G. Osborne and Ray deSouza "Which freezes quicker, hot or cold water?". Retrieved 25 August 2021. High school experiment description, with link to experimental results Adams, Cecil; M. Q. C., Mary (1996). "Which freezes faster, hot water or cold water?". The Straight Dope. Chicago Reader, Inc. Brownridge, James (2010). "A search for the Mpemba effect: When hot water freezes faster than cold water". arXiv:1003.3185 [physics.pop-ph]. Jeng, Monwhea (November 1998). "Can hot water freeze faster than cold water?". in the University of California Usenet


id: mutually-unbiased-bases-20260505-0
file: data/en.wikipedia.org/wiki/Mutually_unbiased_bases-0.md
category: reference
title: Mutually unbiased bases
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mutually_unbiased_bases
date_saved: 2026-05-05T11:05:48.549584+00:00
instance: kb-cron
parent: mutually-unbiased-bases-20260505-0
summary:
In quantum information theory, a set of bases in Hilbert space Cd are said to be mutually unbiased if when a system is prepared in an eigenstate of one of the bases, then all outcomes of the measurement with respect to the other basis are predicted to occur with an equal probability of 1/d. == Overview == The notion of mutually unbiased bases was first introduced by Julian Schwinger in 1960, and the first person to consider applications of mutually unbiased bases was I. D. Ivanovic in the problem of quantum state determination. Mutually unbiased bases (MUBs) and their existence problem is now known to have several closely related problems and equivalent avatars in several other branches of mathematics and quantum sciences, such as SIC-POVMs, finite projective/affine planes, complex Hadamard matrices and more [see section: Related problems]. MUBs are important for quantum key distribution, more specifically in secure quantum key exchange. MUBs are used in many protocols since the outcome is random when a measurement is made in a basis unbiased to that in which the state was prepared. When two remote parties share two non-orthogonal quantum states, attempts by an eavesdropper to distinguish between these by measurements will affect


id: mutually-unbiased-bases-20260505-1
file: data/en.wikipedia.org/wiki/Mutually_unbiased_bases-1.md
category: reference
title: Mutually unbiased bases
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mutually_unbiased_bases
date_saved: 2026-05-05T11:05:48.549584+00:00
instance: kb-cron
parent: mutually-unbiased-bases-20260505-0
summary:
p 1 n 1 < p 2 n 2 < ⋯ < p k n k {\displaystyle p_{1}^{n_{1}}<p_{2}^{n_{2}}<\cdots <p_{k}^{n_{k}}} then the maximum number of mutually unbiased bases which can be constructed satisfies p 1 n 1 + 1 ≤ M ( d ) ≤ d + 1. {\displaystyle p_{1}^{n_{1}}+1\leq {\mathfrak {M}}(d)\leq d+1.} It follows that if the dimension of a Hilbert space d is an integer power of a prime number, then it is possible to find d + 1 mutually unbiased bases. This can be seen in the previous equation, as the prime number decomposition of d simply is d = p n {\displaystyle d=p^{n}} . Therefore, M ( p n ) = p n + 1. {\displaystyle {\mathfrak {M}}(p^{n})=p^{n}+1.} Thus, the maximum number of mutually unbiased bases is known when d is an integer power of a prime number, but it is not known for arbitrary d. The smallest dimension that is not an integer power of a prime is d = 6. This is also the smallest dimension for which the number of mutually unbiased bases is not known. The methods used to determine the number of mutually unbiased bases when d is an integer power of


id: mutually-unbiased-bases-20260505-2
file: data/en.wikipedia.org/wiki/Mutually_unbiased_bases-2.md
category: reference
title: Mutually unbiased bases
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mutually_unbiased_bases
date_saved: 2026-05-05T11:05:48.549584+00:00
instance: kb-cron
parent: mutually-unbiased-bases-20260505-0
summary:
{ | a ⟩ | a ∈ F d } {\displaystyle \{|a\rangle |a\in \mathbb {F} _{d}\}} . We define the operators X a ^ {\displaystyle {\hat {X_{a}}}} and Z b ^ {\displaystyle {\hat {Z_{b}}}} in the following way X a ^ = ∑ c ∈ F d | c + a ⟩ ⟨ c | {\displaystyle {\hat {X_{a}}}=\sum _{c\in \mathbb {F} _{d}}|c+a\rangle \langle c|} Z b ^ = ∑ c ∈ F d χ ( b c ) | c ⟩ ⟨ c | {\displaystyle {\hat {Z_{b}}}=\sum _{c\in \mathbb {F} _{d}}\chi (bc)|c\rangle \langle c|} where χ ( θ ) = exp ⁡ [ 2 π i p ( θ + θ p + θ p 2 + ⋯ + θ p r − 1 ) ] , {\displaystyle \chi (\theta )=\exp \left[{\frac {2\pi i}{p}}\left(\theta +\theta ^{p}+\theta ^{p^{2}}+\cdots +\theta ^{p^{r-1}}\right)\right],} is an additive character over the field and the addition and multiplication in the kets and χ ( ⋅ ) {\displaystyle \chi (\cdot )} is that of F d {\displaystyle \mathbb {F} _{d}} . Then we form d + 1 sets of commuting unitary operators: { Z s ^ | s ∈ F d } {\displaystyle \{{\hat {Z_{s}}}|s\in \mathbb {F} _{d}\}}


id: mutually-unbiased-bases-20260505-3
file: data/en.wikipedia.org/wiki/Mutually_unbiased_bases-3.md
category: reference
title: Mutually unbiased bases
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Mutually_unbiased_bases
date_saved: 2026-05-05T11:05:48.549584+00:00
instance: kb-cron
parent: mutually-unbiased-bases-20260505-0
summary:
== Infinite dimension Hilbert spaces == While there has been investigation into mutually unbiased bases in infinite dimension Hilbert space, their existence remains an open question. It is conjectured that in a continuous Hilbert space, two orthonormal bases | ψ s b ⟩ {\displaystyle |\psi _{s}^{b}\rangle } and | ψ s ′ b ′ ⟩ {\displaystyle |\psi _{s'}^{b'}\rangle } are said to be mutually unbiased if | ⟨ ψ s b | ψ s ′ b ′ ⟩ | 2 = k > 0 , s , s ′ ∈ R {\displaystyle |\langle \psi _{s}^{b}|\psi _{s'}^{b'}\rangle |^{2}=k>0,s,s'\in \mathbb {R} } For the generalized position and momentum eigenstates | q ⟩ , q ∈ R {\displaystyle |q\rangle ,q\in \mathbb {R} } and | p ⟩ , p ∈ R {\displaystyle |p\rangle ,p\in \mathbb {R} } , the value of k is | ⟨ q | p ⟩ | 2 = 1 2 π ℏ {\displaystyle |\langle q|p\rangle |^{2}={\frac {1}{2\pi \hbar }}} The existence of mutually unbiased bases in a continuous Hilbert space remains open for debate, as further research in their existence is required before any conclusions can be reached. Position states | q ⟩ {\displaystyle |q\rangle } and momentum states


id: naga-fireball-20260505-0
file: data/en.wikipedia.org/wiki/Naga_fireball-0.md
category: reference
title: Naga fireball
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Naga_fireball
date_saved: 2026-05-05T11:05:49.767037+00:00
instance: kb-cron
parent: naga-fireball-20260505-0
summary:
Naga fireballs (Thai: บั้งไฟพญานาค; RTGS: bang fai phaya nak), also known as bung fai phaya nak or "Mekong lights" and formerly "ghost lights", are a phenomenon said to be seen annually on the Mekong River. Glowing balls are alleged to naturally rise from the water high into the air. The balls are said to be reddish and to range in size from smaller sparkles up to the size of basketballs. They quickly rise up to a couple of hundred metres before disappearing. The number of fireballs reported varies between tens and thousands per night. The phenomenon is locally attributed to phaya nak, a giant serpent (Nāga) said to live in the Mekong. == Description == The fireballs are most often reported around the night of Wan Ok Phansa at the end of Vassa in late-October. Naga fireballs have been reported over an approximately 250 km (160 mi) long section of the Mekong River centered approximately on Phon Phisai in the Phon Phisai District. Fireballs have also been reported rising from smaller rivers, lakes and ponds in the region. The fireballs were called "ghost lights" by locals until the mid-1980s, when the local council officially named them "phaya nak lights". In


id: navier-stokes-existence-and-smoothness-20260505-0
file: data/en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness-0.md
category: reference
title: Navier–Stokes existence and smoothness
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness
date_saved: 2026-05-05T11:05:51.019518+00:00
instance: kb-cron
parent: navier-stokes-existence-and-smoothness-20260505-0
summary:
The Navier–Stokes existence and smoothness problem concerns the mathematical properties of solutions to the Navier–Stokes equations, a system of partial differential equations that describe the motion of a fluid in space. Solutions to the Navier–Stokes equations are used in many practical applications. However, theoretical understanding of the solutions to these equations is incomplete. In particular, solutions of the Navier–Stokes equations often include turbulence, which remains one of the greatest unsolved problems in physics, despite its immense importance in science and engineering. Even more basic (and seemingly intuitive) properties of the solutions to Navier–Stokes have never been proven. For the three-dimensional system of equations, and given some initial conditions, mathematicians have neither proved that smooth solutions always exist, nor found any counter-examples. This is called the Navier–Stokes existence and smoothness problem. Since understanding the Navier–Stokes equations is considered to be the first step to understanding the elusive phenomenon of turbulence, the Clay Mathematics Institute in May 2000 made this problem one of its seven Millennium Prize problems in mathematics. It offered a US$1,000,000 prize to the first person providing a solution for a specific statement of the problem: Prove or give a counter-example of the following statement: In three space dimensions


id: navier-stokes-existence-and-smoothness-20260505-1
file: data/en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness-1.md
category: reference
title: Navier–Stokes existence and smoothness
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness
date_saved: 2026-05-05T11:05:51.019518+00:00
instance: kb-cron
parent: navier-stokes-existence-and-smoothness-20260505-0
summary:
Due to this last property, the solutions for the Navier–Stokes equations are searched in the set of solenoidal ("divergence-free") functions. For this flow of a homogeneous medium, density and viscosity are constants. Since only its gradient appears, the pressure p can be eliminated by taking the curl of both sides of the Navier–Stokes equations. In this case the Navier–Stokes equations reduce to the vorticity-transport equations. The Navier–Stokes equations are nonlinear, meaning that the terms in the equations do not have a simple linear relationship with each other. This means that the equations cannot be solved using traditional linear techniques, and more advanced methods must be used instead. This nonlinearity allows the equations to describe a wide range of fluid dynamics phenomena, including the formation of shock waves and other complex flow patterns. One way to understand the nonlinearity of the Navier–Stokes equations is to consider the term ( v ⋅ ∇ ) v {\displaystyle (\mathbf {v} \cdot \nabla )\mathbf {v} } in the equations. This term represents the acceleration of the fluid, and it is a product of the velocity vector v and the gradient operator ∇. Because the gradient operator is a linear operator, the term (v · ∇)v


id: navier-stokes-existence-and-smoothness-20260505-2
file: data/en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness-2.md
category: reference
title: Navier–Stokes existence and smoothness
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness
date_saved: 2026-05-05T11:05:51.019518+00:00
instance: kb-cron
parent: navier-stokes-existence-and-smoothness-20260505-0
summary:
d U i d t = − 1 ρ ∑ j = 1 N ( ∂ p ∂ x ) j ∫ Ω ϕ j ∂ ϕ i ∂ x d Ω + ν ∑ j = 1 N ∫ Ω ( ∂ 2 u ∂ x 2 ) ϕ j ∂ 2 ϕ i ∂ x 2 d Ω + ∫ Ω f x ϕ i d Ω {\displaystyle {\frac {dU_{i}}{dt}}=-{\frac {1}{\rho }}\sum _{j=1}^{N}\left({\frac {\partial p}{\partial x}}\right)j\int {\Omega }\phi _{j}{\frac {\partial \phi _{i}}{\partial x}}d\Omega +\nu \sum _{j=1}^{N}\int _{\Omega }\left({\frac {\partial ^{2}u}{\partial x^{2}}}\right)\phi _{j}{\frac {\partial ^{2}\phi _{i}}{\partial x^{2}}}d\Omega +\int {\Omega }f_{x}\phi _{i}d\Omega } where Ω {\displaystyle \Omega } is the domain, and the integrals are over the domain. This system of ordinary differential equations can be solved using techniques such as the finite element method or spectral methods. Here, we will use the finite difference method. To do this, we can divide the time interval [ t 0 , t f ] {\displaystyle [t_{0},t_{f}]} into a series of smaller time steps, and approximate the derivative at each time step using a finite difference formula: U i + 1 − U i Δ t ≈ − 1 ρ ∑ j =


id: navier-stokes-existence-and-smoothness-20260505-3
file: data/en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness-3.md
category: reference
title: Navier–Stokes existence and smoothness
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness
date_saved: 2026-05-05T11:05:51.019518+00:00
instance: kb-cron
parent: navier-stokes-existence-and-smoothness-20260505-0
summary:
There exists a constant E ∈ ( 0 , ∞ ) {\displaystyle E\in (0,\infty )} such that ∫ R 3 | v ( x , t ) | 2 d x < E {\displaystyle \int _{\mathbb {R} ^{3}}\vert \mathbf {v} (x,t)\vert ^{2}\,dx<E} for all t ≥ 0 . {\displaystyle t\geq 0\,.} Condition 1 implies that the functions are smooth and globally defined and condition 2 means that the kinetic energy of the solution is globally bounded. === The Millennium Prize conjectures in the whole space === (A) Existence and smoothness of the Navier–Stokes solutions in R 3 {\displaystyle \mathbb {R} ^{3}} Let f ( x , t ) ≡ 0 {\displaystyle \mathbf {f} (x,t)\equiv 0} . For any initial condition v 0 ( x ) {\displaystyle \mathbf {v} _{0}(x)} satisfying the above hypotheses there exist smooth and globally defined solutions to the Navier–Stokes equations, i.e. there is a velocity vector v ( x , t ) {\displaystyle \mathbf {v} (x,t)} and a pressure p ( x , t ) {\displaystyle p(x,t)} satisfying conditions 1 and 2 above. (B) Breakdown of the Navier–Stokes solutions in R 3 {\displaystyle \mathbb {R} ^{3}} There exists an initial condition v 0 ( x )


id: navier-stokes-existence-and-smoothness-20260505-4
file: data/en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness-4.md
category: reference
title: Navier–Stokes existence and smoothness
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness
date_saved: 2026-05-05T11:05:51.019518+00:00
instance: kb-cron
parent: navier-stokes-existence-and-smoothness-20260505-0
summary:
where ρ {\displaystyle \rho } is the density, ν {\displaystyle \nu } is the kinematic viscosity, and f ( x , y , t ) = ( f x ( x , y , t ) , f y ( x , y , t ) ) {\displaystyle \mathbf {f} (x,y,t)=(f_{x}(x,y,t),f_{y}(x,y,t))} is an external force. The boundary conditions might specify that the velocity is fixed at the walls of the domain, or that the pressure is fixed at certain points. To solve these equations numerically, we can divide the domain into a series of smaller elements, and solve the equations locally within each element. For example, using a finite element method, we might represent the velocity and pressure fields as: u ( x , y , t ) = ∑ i = 1 N U i ( t ) ϕ i ( x , y ) {\displaystyle u(x,y,t)=\sum _{i=1}^{N}U_{i}(t)\phi _{i}(x,y)} v ( x , y , t ) = ∑ i = 1 N V i ( t ) ϕ i ( x , y ) {\displaystyle v(x,y,t)=\sum _{i=1}^{N}V_{i}(t)\phi _{i}(x,y)} p ( x , y , t ) = ∑ i = 1 N P i ( t ) ϕ


id: navier-stokes-existence-and-smoothness-20260505-5
file: data/en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness-5.md
category: reference
title: Navier–Stokes existence and smoothness
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Navier–Stokes_existence_and_smoothness
date_saved: 2026-05-05T11:05:51.019518+00:00
instance: kb-cron
parent: navier-stokes-existence-and-smoothness-20260505-0
summary:
== Partial results == In 1934, Jean Leray proved that there are smooth and globally defined solutions to the Navier–Stokes equations under the assumption that the initial velocity v 0 ( x ) {\displaystyle \mathbf {v} _{0}(x)} is sufficiently small. He also proved the existence of so-called weak solutions to the Navier–Stokes equations, which may not satisfy the equations pointwise but do satisfy them in mean value. In the 1960s, the finite difference method was proven to be convergent for the Navier–Stokes equations and the equations were numerically solved. It was also proven that there are smooth and globally defined solutions to the Navier–Stokes equations in 2 dimensions. It is known that given an initial velocity v 0 ( x ) {\displaystyle \mathbf {v} _{0}(x)} there exists a finite "blowup time" T, depending on v 0 ( x ) {\displaystyle \mathbf {v} _{0}(x)} , such that the Navier–Stokes equations on R 3 × ( 0 , T ) {\displaystyle \mathbb {R} ^{3}\times (0,T)} have smooth solutions v ( x , t ) {\displaystyle \mathbf {v} (x,t)} and p ( x , t ) {\displaystyle p(x,t)} . These solutions may, however, not hold for values of t {\displaystyle t} beyond the


id: numerical-sign-problem-20260505-0
file: data/en.wikipedia.org/wiki/Numerical_sign_problem-0.md
category: reference
title: Numerical sign problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Numerical_sign_problem
date_saved: 2026-05-05T11:06:08.014515+00:00
instance: kb-cron
parent: numerical-sign-problem-20260505-0
summary:
In applied mathematics, the numerical sign problem is the problem of numerically evaluating the integral of a highly oscillatory function of a large number of variables. Numerical methods fail because of the near-cancellation of the positive and negative contributions to the integral. Each has to be integrated to very high precision in order for their difference to be obtained with useful accuracy. The sign problem is one of the major unsolved problems in the physics of many-particle systems. It often arises in calculations of the properties of a quantum mechanical system with large number of strongly interacting fermions, or in field theories involving a non-zero density of strongly interacting fermions. == Overview == In physics the sign problem is typically (but not exclusively) encountered in calculations of the properties of a quantum mechanical system with large number of strongly interacting fermions, or in field theories involving a non-zero density of strongly interacting fermions. Because the particles are strongly interacting, perturbation theory is inapplicable, and one is forced to use brute-force numerical methods. Because the particles are fermions, their wavefunction changes sign when any two fermions are interchanged (due to the anti-symmetry of the wave function, see Pauli principle). So unless


id: numerical-sign-problem-20260505-1
file: data/en.wikipedia.org/wiki/Numerical_sign_problem-1.md
category: reference
title: Numerical sign problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Numerical_sign_problem
date_saved: 2026-05-05T11:06:08.014515+00:00
instance: kb-cron
parent: numerical-sign-problem-20260505-0
summary:
⟨ A ⟩ ρ = ∫ D σ A [ σ ] exp ⁡ ( i θ [ σ ] ) p [ σ ] ∫ D σ exp ⁡ ( i θ [ σ ] ) p [ σ ] = ⟨ A [ σ ] exp ⁡ ( i θ [ σ ] ) ⟩ p ⟨ exp ⁡ ( i θ [ σ ] ) ⟩ p . {\displaystyle \langle A\rangle _{\rho }={\frac {\int D\sigma A[\sigma ]\exp(i\theta [\sigma ])\,p[\sigma ]}{\int D\sigma \exp(i\theta [\sigma ])\,p[\sigma ]}}={\frac {\langle A[\sigma ]\exp(i\theta [\sigma ])\rangle _{p}}{\langle \exp(i\theta [\sigma ])\rangle _{p}}}.} Note that the desired expectation value is now a ratio where the numerator and denominator are expectation values that both use a positive weighting function p [ σ ] {\displaystyle p[\sigma ]} . However, the phase exp ⁡ ( i θ [ σ ] ) {\displaystyle \exp(i\theta [\sigma ])} is a highly oscillatory function in the configuration space, so if one uses Monte Carlo methods to evaluate the numerator and denominator, each of them will evaluate to a very small number, whose exact value is swamped by the noise inherent in the Monte Carlo sampling process. The "badness" of the sign problem


id: physics-beyond-the-standard-model-20260505-0
file: data/en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model-0.md
category: reference
title: Physics beyond the Standard Model
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model
date_saved: 2026-05-05T11:06:09.206638+00:00
instance: kb-cron
parent: physics-beyond-the-standard-model-20260505-0
summary:
Physics beyond the Standard Model (BSM) refers to the theoretical developments needed to explain the deficiencies of the Standard Model, such as the inability to explain the fundamental parameters of the Standard Model, the strong CP problem, neutrino oscillations, matter–antimatter asymmetry, and the nature of dark matter and dark energy. Another problem lies within the mathematical framework of the Standard Model itself: the Standard Model is inconsistent with that of general relativity, and one or both theories break down under certain conditions, such as spacetime singularities like the Big Bang and black hole event horizons. Theories that lie beyond the Standard Model include various extensions of the standard model through supersymmetry, such as the Minimal Supersymmetric Standard Model (MSSM) and Next-to-Minimal Supersymmetric Standard Model (NMSSM), and entirely novel explanations, such as string theory, M-theory, and extra dimensions. As these theories tend to reproduce the entirety of current phenomena, the question of which theory is the right one, or at least the "best step" towards a Theory of Everything, can only be settled via experiments, and is one of the most active areas of research in both theoretical and experimental physics. == Problems with the Standard Model == Despite being the


id: physics-beyond-the-standard-model-20260505-1
file: data/en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model-1.md
category: reference
title: Physics beyond the Standard Model
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model
date_saved: 2026-05-05T11:06:09.206638+00:00
instance: kb-cron
parent: physics-beyond-the-standard-model-20260505-0
summary:
B meson decay etc. – results from a BaBar experiment may suggest a surplus over Standard Model predictions of a type of particle decay ( B → D(*) τ− ντ ). In this, an electron and positron collide, resulting in a B meson and an antimatter B meson, which then decays into a D meson and a tau lepton as well as a tau antineutrino. While the level of certainty of the excess (3.4 σ in statistical jargon) is not enough to declare a break from the Standard Model, the results are a potential sign of something amiss and are likely to affect existing theories, including those attempting to deduce the properties of Higgs bosons. In 2015, LHCb reported observing a 2.1 σ excess in the same ratio of branching fractions. The Belle experiment also reported an excess. In 2017 a meta analysis of all available data reported a cumulative 5 σ deviation from SM. Neutron lifetime puzzle – Free neutrons are not stable but decay after some time. Currently there are two methods used to measure this lifetime ("bottle" versus "beam") that give different values not within each other's error margin. Currently the lifetime from the bottle method is


id: physics-beyond-the-standard-model-20260505-2
file: data/en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model-2.md
category: reference
title: Physics beyond the Standard Model
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model
date_saved: 2026-05-05T11:06:09.206638+00:00
instance: kb-cron
parent: physics-beyond-the-standard-model-20260505-0
summary:
Hierarchy problem – the Standard Model introduces particle masses through a process known as spontaneous symmetry breaking caused by the Higgs field. Within the Standard Model, the mass of the Higgs particle gets some very large quantum corrections due to the presence of virtual particles (mostly virtual top quarks). These corrections are much larger than the actual mass of the Higgs. This means that the bare mass parameter of the Higgs in the Standard Model must be fine tuned in such a way that almost completely cancels the quantum corrections. This level of fine-tuning is deemed unnatural by many theorists. The problem cannot be formulated in the strict context of the Standard Model, for the Higgs mass cannot be calculated. In a sense, the problem amounts to the worry that a future theory of fundamental particles, in which the Higgs boson mass will be calculable, should not have excessive fine-tunings. Number of parameters – the Standard Model depends on 19 parameter numbers. Their values are known from experiment, but the origin of the values is unknown. Some theorists have tried to find relations between different parameters, for example, between the masses of particles in different generations or calculating particle masses,


id: physics-beyond-the-standard-model-20260505-3
file: data/en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model-3.md
category: reference
title: Physics beyond the Standard Model
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model
date_saved: 2026-05-05T11:06:09.206638+00:00
instance: kb-cron
parent: physics-beyond-the-standard-model-20260505-0
summary:
== Neutrinos == In the Standard Model, neutrinos cannot spontaneously change flavor. Measurements however indicated that neutrinos do spontaneously change flavor, in what is called neutrino oscillations. Neutrino oscillations are usually explained using massive neutrinos. In the Standard Model, neutrinos have exactly zero mass, as the Standard Model only contains left-handed neutrinos. With no suitable right-handed partner, it is impossible to add a renormalizable mass term to the Standard Model. These measurements only give the mass differences between the different flavours. The best constraint on the absolute mass of the neutrinos comes from precision measurements of tritium decay, providing an upper limit 2 eV, which makes them at least five orders of magnitude lighter than the other particles in the Standard Model. This necessitates an extension of the Standard Model, which not only needs to explain how neutrinos get their mass, but also why the mass is so small. One approach to add masses to the neutrinos, the so-called seesaw mechanism, is to add right-handed neutrinos and have these couple to left-handed neutrinos with a Dirac mass term. The right-handed neutrinos have to be sterile, meaning that they do not participate in any of the Standard Model interactions. Because they


id: physics-beyond-the-standard-model-20260505-4
file: data/en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model-4.md
category: reference
title: Physics beyond the Standard Model
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model
date_saved: 2026-05-05T11:06:09.206638+00:00
instance: kb-cron
parent: physics-beyond-the-standard-model-20260505-0
summary:
Extensions, revisions, replacements, and reorganizations of the Standard Model exist in attempt to correct for these and other issues. String theory is one such reinvention, and many theoretical physicists think that such theories are the next theoretical step toward a true Theory of Everything. Among the numerous variants of string theory, M-theory, whose mathematical existence was first proposed at a String Conference in 1995 by Edward Witten, is believed by many to be a proper "ToE" candidate, notably by physicists Brian Greene and Stephen Hawking. Though a full mathematical description is not yet known, solutions to the theory exist for specific cases. Recent works have also proposed alternate string models, some of which lack the various harder-to-test features of M-theory (e.g. the existence of Calabi–Yau manifolds, many extra dimensions, etc.) including works by well-published physicists such as Lisa Randall. === Unified Gravity === Unified Gravity treats gravity as a gauge field from a set of compact U(1) symmetries in an extended spinor space. This allows creating a Lagrangian that contains all known fundamental interactions of nature. == See also == == Footnotes == == References == == Further reading == Lisa Randall (2005). Warped Passages: Unraveling the Mysteries of the


id: problem-of-time-20260505-0
file: data/en.wikipedia.org/wiki/Problem_of_time-0.md
category: reference
title: Problem of time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Problem_of_time
date_saved: 2026-05-05T11:06:10.503318+00:00
instance: kb-cron
parent: problem-of-time-20260505-0
summary:
In theoretical physics, the problem of time is a conceptual conflict between quantum mechanics and general relativity. Quantum mechanics regards the flow of time as universal and absolute, whereas general relativity regards the flow of time as malleable and relative. This problem raises the question of what time really is in a physical sense and whether it is truly a real, distinct phenomenon. It also involves the related question of why time seems to flow in a single direction, despite the fact that no known physical laws at the microscopic level seem to require a single direction. == Time in quantum mechanics == In classical mechanics, a special status is assigned to time in the sense that it is treated as a classical background parameter, external to the system itself. This special role is seen in the standard Copenhagen interpretation of quantum mechanics: all measurements of observables are made at certain instants of time and probabilities are only assigned to such measurements. Furthermore, the Hilbert space used in quantum theory relies on a complete set of observables which commute at a specific time. == Time in general relativity == In general relativity time is no longer a unique background parameter,


id: problem-of-time-20260505-1
file: data/en.wikipedia.org/wiki/Problem_of_time-1.md
category: reference
title: Problem of time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Problem_of_time
date_saved: 2026-05-05T11:06:10.503318+00:00
instance: kb-cron
parent: problem-of-time-20260505-0
summary:
== Proposed solutions to the problem of time == Work started by Don Page and William Wootters suggests that the universe appears to evolve for observers on the inside because of energy entanglement between an evolving system and a clock system, both within the universe. In this way the overall system can remain timeless while parts experience time via entanglement. The issue remains an open question closely related to attempted theories of quantum gravity. In other words, time is an entanglement phenomenon, which places all equal clock readings (of correctly prepared clocks – or any objects usable as clocks) into the same history. In 2013, at the Istituto Nazionale di Ricerca Metrologica (INRIM) in Turin, Italy, Ekaterina Moreva, together with Giorgio Brida, Marco Gramegna, Vittorio Giovannetti, Lorenzo Maccone, and Marco Genovese performed the first experimental test of Page and Wootters' ideas. They confirmed for photons that time is an emergent phenomenon for internal observers of a quantum system but is absent for external observers, which is consistent with the predictions of the Wheeler–DeWitt equation. Consistent discretizations approach developed by Jorge Pullin and Rodolfo Gambini have no constraints. These are lattice approximation techniques for quantum gravity. In the canonical approach, if


id: proton-spin-crisis-20260505-0
file: data/en.wikipedia.org/wiki/Proton_spin_crisis-0.md
category: reference
title: Proton spin crisis
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Proton_spin_crisis
date_saved: 2026-05-05T11:06:11.743787+00:00
instance: kb-cron
parent: proton-spin-crisis-20260505-0
summary:
The proton spin crisis (or proton spin puzzle) is a theoretical crisis precipitated by a 1987 experiment by the European Muon Collaboration (EMC), which tried to determine the distribution of spin within the proton. Physicists expected that the quarks carry all of a proton's spin. However, not only was the total proton spin carried by quarks far smaller than 100%, these results were consistent with almost zero (4–24%) proton spin being carried by quarks. This surprising and puzzling result was termed the "proton spin crisis". The problem is considered one of the important unsolved problems in physics. == Background == A key question is how the nucleons' spins are distributed amongst their constituent parts ("partons": quarks and gluons). The components of the proton's spin are the expectation values of the individual sources of angular momentum. These values depend on the renormalization scale, because their operators are not separately conserved. Physicists originally expected that valence quarks would carry all of the nucleon spin. A proton is built from three valence quarks (two up quarks and one down quark), virtual gluons, and virtual (or sea) quarks and antiquarks (virtual particles do not influence the proton's quantum numbers). The ruling hypothesis was that


id: qcd-matter-20260505-0
file: data/en.wikipedia.org/wiki/QCD_matter-0.md
category: reference
title: QCD matter
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/QCD_matter
date_saved: 2026-05-05T11:06:12.997806+00:00
instance: kb-cron
parent: qcd-matter-20260505-0
summary:
Quark matter or QCD matter refers to matter governed by quantum chromodynamics and involving quarks and gluons. At different temperatures and densities quark matter takes different forms, including a hadron gas, nuclear matter, quark-gluon plasma, and regions of color superconductivity. Quarks are liberated into quark matter at extremely high temperatures and/or densities, and some of them are still only theoretical as they require conditions so extreme that they cannot be produced in any laboratory, especially not at equilibrium conditions. Under these extreme conditions, the familiar structure of matter, where the basic constituents are nuclei (consisting of nucleons which are bound states of quarks) and electrons, is disrupted. In quark matter it is more appropriate to treat the quarks themselves as the basic degrees of freedom. In the Standard Model of particle physics, the strong force is described by the theory of QCD. At ordinary temperatures or densities this force just confines the quarks into composite particles (hadrons) of size around 10−15 m = 1 femtometer = 1 fm (corresponding to the QCD energy scale ΛQCD ≈ 200 MeV) and its effects are not noticeable at longer distances. However, when the temperature reaches the QCD energy scale (T of order 1012


id: qcd-matter-20260505-1
file: data/en.wikipedia.org/wiki/QCD_matter-1.md
category: reference
title: QCD matter
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/QCD_matter
date_saved: 2026-05-05T11:06:12.997806+00:00
instance: kb-cron
parent: qcd-matter-20260505-0
summary:
== Thermodynamics == The context for understanding the thermodynamics of quark matter is the Standard Model of particle physics, which contains six different flavors of quarks, as well as leptons like electrons and neutrinos. These interact via the strong interaction, electromagnetism, and also the weak interaction which allows one flavor of quark to turn into another. Electromagnetic interactions occur between particles that carry electrical charge; strong interactions occur between particles that carry color charge. The correct thermodynamic treatment of quark matter depends on the physical context. For large quantities that exist for long periods of time (the "thermodynamic limit"), we must take into account the fact that the only conserved charges in the standard model are quark number (equivalent to baryon number), electric charge, the eight color charges, and lepton number. Each of these can have an associated chemical potential. However, large volumes of matter must be electrically and color-neutral, which determines the electric and color charge chemical potentials. This leaves a three-dimensional phase space, parameterized by quark chemical potential, lepton chemical potential, and temperature. In compact stars quark matter would occupy cubic kilometers and exist for millions of years, so the thermodynamic limit is appropriate. However, the neutrinos escape,


id: qcd-matter-20260505-2
file: data/en.wikipedia.org/wiki/QCD_matter-2.md
category: reference
title: QCD matter
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/QCD_matter
date_saved: 2026-05-05T11:06:12.997806+00:00
instance: kb-cron
parent: qcd-matter-20260505-0
summary:
== Theoretical challenges: calculation techniques == The phase structure of quark matter remains mostly conjectural because it is difficult to perform calculations predicting the properties of quark matter. The reason is that QCD, the theory describing the dominant interaction between quarks, is strongly coupled at the densities and temperatures of greatest physical interest, and hence it is very hard to obtain any predictions from it. Here are brief descriptions of some of the standard approaches. === Lattice gauge theory === The only first-principles calculational tool currently available is lattice QCD, i.e. brute-force computer calculations. Because of a technical obstacle known as the fermion sign problem, this method can only be used at low density and high temperature (μ < T), and it predicts that the crossover to the quark–gluon plasma will occur around T = 150 MeV However, it cannot be used to investigate the interesting color-superconducting phase structure at high density and low temperature. === Weak coupling theory === Because QCD is asymptotically free it becomes weakly coupled at unrealistically high densities, and diagrammatic methods can be used. Such methods show that the CFL phase occurs at very high density. At high temperatures, however, diagrammatic methods are still not


id: quark-star-20260505-0
file: data/en.wikipedia.org/wiki/Quark_star-0.md
category: reference
title: Quark star
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Quark_star
date_saved: 2026-05-05T11:06:14.297455+00:00
instance: kb-cron
parent: quark-star-20260505-0
summary:
A quark star is a hypothetical type of compact, exotic star, where extremely high core temperature and pressure have forced nuclear particles to form quark matter, a continuous state of matter consisting of free quarks. == Background == Some massive stars collapse to form neutron stars at the end of their life cycle, as has been both observed and explained theoretically. Under the extreme temperatures and pressures inside neutron stars, the neutrons are normally kept apart by a degeneracy pressure, stabilizing the star and hindering further gravitational collapse. However, it is hypothesized that under even more extreme temperature and pressure, the degeneracy pressure of the neutrons is overcome, and the neutrons are forced to merge and dissolve into their constituent quarks, creating an ultra-dense phase of quark matter based on densely packed quarks. In this state, a new equilibrium is supposed to emerge, as a new degeneracy pressure between the quarks, as well as repulsive electromagnetic forces, will occur and hinder total gravitational collapse that would form a stellar black hole. If these ideas are correct, quark stars might occur, and be observable, somewhere in the universe. Numerical simulations of the physics inside neutron stars predict quark deconfinement is likely.Such


id: quark-star-20260505-1
file: data/en.wikipedia.org/wiki/Quark_star-1.md
category: reference
title: Quark star
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Quark_star
date_saved: 2026-05-05T11:06:14.297455+00:00
instance: kb-cron
parent: quark-star-20260505-0
summary:
At least under the assumptions mentioned above, the probability of a given neutron star being a quark star is low, so in the Milky Way there would only be a small population of quark stars. If it is correct, however, that overdense neutron stars can turn into quark stars, that makes the possible number of quark stars higher than was originally thought, as observers would be looking for the wrong type of star. A neutron star without deconfinement to quarks and higher densities cannot have a rotational period shorter than a millisecond; even with the unimaginable gravity of such a condensed object the centrifugal force of faster rotation would eject matter from the surface, so detection of a pulsar of millisecond or less period would be strong evidence of a quark star. Observations released by the Chandra X-ray Observatory on April 10, 2002, detected two possible quark stars, designated RX J1856.5−3754 and 3C 58, which had previously been thought to be neutron stars. Based on the known laws of physics, the former appeared much smaller and the latter much colder than it should be, suggesting that they are composed of material denser than neutron-degenerate matter. However, these observations are met


id: shower-curtain-effect-20260505-0
file: data/en.wikipedia.org/wiki/Shower-curtain_effect-0.md
category: reference
title: Shower-curtain effect
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Shower-curtain_effect
date_saved: 2026-05-05T11:06:15.549332+00:00
instance: kb-cron
parent: shower-curtain-effect-20260505-0
summary:
The shower-curtain effect in physics describes the phenomenon of a shower curtain being blown inward when a shower is running. The problem of identifying the cause of this effect has been featured in Scientific American magazine, with several hypotheses given to explain the phenomenon but no definite conclusion. == Hypotheses == === Buoyancy hypothesis === Also called chimney effect or stack effect, observes that warm air (from the hot shower) rises out over the shower curtain as cooler air (near the floor) pushes in under the curtain to replace the rising air. By pushing the curtain in towards the shower, the (short range) vortex and Coandă effects become more significant. However, the shower-curtain effect persists when cold water is used, implying that this is not the sole mechanism. === Bernoulli effect hypothesis === The most popular explanation given for the shower-curtain effect is Bernoulli's principle. Bernoulli's principle states that an increase in velocity results in a decrease in pressure. This theory presumes that the water flowing out of a shower head causes the air through which the water moves to start flowing in the same direction as the water. This movement would be parallel to the plane of the shower


id: sic-povm-20260505-0
file: data/en.wikipedia.org/wiki/SIC-POVM-0.md
category: reference
title: SIC-POVM
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/SIC-POVM
date_saved: 2026-05-05T11:06:16.798078+00:00
instance: kb-cron
parent: sic-povm-20260505-0
summary:
In the context of quantum mechanics and quantum information theory, symmetric, informationally complete, positive operator-valued measures (SIC-POVMs) are a particular type of generalized measurement (POVM). SIC-POVMs are particularly notable thanks to their defining features of (1) being informationally complete; (2) having the minimal number of outcomes compatible with informational completeness, and (3) being highly symmetric. In this context, informational completeness is the property of a POVM of allowing to fully reconstruct input states from measurement data. The properties of SIC-POVMs make them an interesting candidate for a "standard quantum measurement", utilized in the study of foundational quantum mechanics, most notably in QBism. SIC-POVMs have several applications in the context of quantum state tomography and quantum cryptography, and a possible connection has been discovered with Hilbert's twelfth problem. == Definition == A POVM over a d {\displaystyle d} -dimensional Hilbert space H {\displaystyle {\mathcal {H}}} is a set of m {\displaystyle m} positive-semidefinite operators { F i } i = 1 m {\displaystyle \left\{F_{i}\right\}_{i=1}^{m}} that sum to the identity: ∑ i = 1 m F i = I . {\displaystyle \sum _{i=1}^{m}F_{i}=I.} If a POVM consists of at least d 2 {\displaystyle d^{2}} operators which span the space of self-adjoint operators


id: sic-povm-20260505-1
file: data/en.wikipedia.org/wiki/SIC-POVM-1.md
category: reference
title: SIC-POVM
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/SIC-POVM
date_saved: 2026-05-05T11:06:16.798078+00:00
instance: kb-cron
parent: sic-povm-20260505-0
summary:
ρ = I | ρ ) = ∑ α [ ( d + 1 ) Π α − I ] ( Π α | ρ ) d = ∑ α [ ( d + 1 ) Π α − I ] T r ( Π α ρ ) d = ∑ α p α [ ( d + 1 ) Π α − I ] where p α = T r ( Π α ρ ) / d = − I + ( d + 1 ) ∑ α p α | ψ α ⟩ ⟨ ψ α | = ∑ α [ ( d + 1 ) p α − 1 d ] | ψ α ⟩ ⟨ ψ α | {\displaystyle {\begin{aligned}\rho =I|\rho )&=\displaystyle \sum _{\alpha }\left[(d+1)\Pi _{\alpha }-I\right]{\frac {(\Pi _{\alpha }|\rho )}{d}}\\&=\displaystyle \sum _{\alpha }\left[(d+1)\Pi _{\alpha }-I\right]{\frac {\mathrm {Tr} (\Pi _{\alpha }\rho )}{d}}\\&=\displaystyle \sum _{\alpha }p_{\alpha }\left[(d+1)\Pi _{\alpha }-I\right]\quad {\text{ where }}p_{\alpha }=\mathrm {Tr} (\Pi _{\alpha }\rho )/d\\&=\displaystyle -I+(d+1)\sum _{\alpha }p_{\alpha }|\psi _{\alpha }\rangle \langle \psi _{\alpha }|\\&=\displaystyle \sum _{\alpha }\left[(d+1)p_{\alpha }-{\frac {1}{d}}\right]|\psi _{\alpha }\rangle \langle \psi _{\alpha }|\end{aligned}}} where | ρ ) {\displaystyle |\rho )} is the Dirac notation for the density operator viewed in the


id: sic-povm-20260505-2
file: data/en.wikipedia.org/wiki/SIC-POVM-2.md
category: reference
title: SIC-POVM
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/SIC-POVM
date_saved: 2026-05-05T11:06:16.798078+00:00
instance: kb-cron
parent: sic-povm-20260505-0
summary:
For every dimension d ≥ 2 {\displaystyle d\geq 2} there exists a SIC-POVM whose elements are the orbit of a positive rank-one operator E 0 {\displaystyle E_{0}} under the Weyl–Heisenberg group H d {\displaystyle H_{d}} . What is more, E 0 {\displaystyle E_{0}} commutes with an element T of the Jacobi group J d = H d ⋊ S L ( 2 , Z d ) {\displaystyle J_{d}=H_{d}\rtimes SL(2,\mathbb {Z} _{d})} . The action of T on H d {\displaystyle H_{d}} modulo the center has order three. Utilizing the notion of group covariance on Z d × Z d {\displaystyle \mathbb {Z} _{d}\times \mathbb {Z} _{d}} , this can be restated as For any dimension d ∈ N {\displaystyle d\in \mathbb {N} } , let { k } k = 0 d − 1 {\displaystyle \left\{k\right\}_{k=0}^{d-1}} be an orthonormal basis for C d {\displaystyle \mathbb {C} ^{d}} , and define ω = e 2 π i d , D j , k = ω j k 2 ∑ m = 0 d − 1 ω j m | k + m ( mod d ) ⟩ ⟨ m | {\displaystyle \displaystyle \omega =e^{\frac {2\pi i}{d}},\quad \quad D_{j,k}=\omega ^{\frac {jk}{2}}\sum _{m=0}^{d-1}\omega


id: simon-problems-20260505-0
file: data/en.wikipedia.org/wiki/Simon_problems-0.md
category: reference
title: Simon problems
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Simon_problems
date_saved: 2026-05-05T11:06:18.069142+00:00
instance: kb-cron
parent: simon-problems-20260505-0
summary:
In mathematics, the Simon problems (or Simon's problems) are a series of fifteen questions posed in the year 2000 by Barry Simon, an American mathematical physicist. Inspired by other collections of mathematical problems and open conjectures, such as the famous list by David Hilbert, the Simon problems concern quantum operators. Eight of the problems pertain to anomalous spectral behavior of Schrödinger operators, and five concern operators that incorporate the Coulomb potential. In 2014, Artur Avila won a Fields Medal for work including the solution of three Simon problems. Among these was the problem of proving that the set of energy levels of one particular abstract quantum system was, in fact, the Cantor set, a challenge known as the "Ten Martini Problem" after the reward that Mark Kac offered for solving it. The 2000 list was a refinement of a similar set of problems that Simon had posed in 1984. == Context == Background definitions for the "Coulomb energies" problems ( N {\displaystyle N} non-relativistic particles (electrons) in R 3 {\displaystyle \mathbb {R} ^{3}} with spin 1 / 2 {\displaystyle 1/2} and an infinitely heavy nucleus with charge Z {\displaystyle Z} and Coulombic mutual interaction): H f ( N ) {\displaystyle


id: amorphous-solid-20260505-0
file: data/en.wikipedia.org/wiki/Amorphous_solid-0.md
category: reference
title: Amorphous solid
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Amorphous_solid
date_saved: 2026-05-05T11:06:19.245432+00:00
instance: kb-cron
parent: amorphous-solid-20260505-0
summary:
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is a characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymously with amorphous solid; however, these terms refer specifically to amorphous materials that undergo a glass transition. Examples of amorphous solids include glasses, metallic glasses, and certain types of plastics and polymers. == Etymology == The term "Amorphous" comes from the Greek a ("without"), and morphé ("shape, form"). == Structure == Amorphous materials have an internal structure of molecular-scale structural blocks that can be similar to the basic structural units in the crystalline phase of the same compound. Unlike in crystalline materials, however, no long-range regularity exists: amorphous materials cannot be described by the repetition of a finite unit cell. Statistical measures, such as the atomic density function and radial distribution function, are more useful in describing the structure of amorphous solids. Although amorphous materials lack long range order, they exhibit localized order on small length scales. By convention, short range order extends only to the nearest neighbor shell, typically only 1-2 atomic spacings. Medium range order may extend beyond the short range


id: amorphous-solid-20260505-1
file: data/en.wikipedia.org/wiki/Amorphous_solid-1.md
category: reference
title: Amorphous solid
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Amorphous_solid
date_saved: 2026-05-05T11:06:19.245432+00:00
instance: kb-cron
parent: amorphous-solid-20260505-0
summary:
=== Computational techniques === Simulation and modeling techniques are often combined with experimental methods to characterize structures of amorphous materials. Commonly used computational techniques include density functional theory, molecular dynamics, and reverse Monte Carlo. == Uses and observations == === Amorphous thin films === Amorphous phases are important constituents of thin films. Thin films are solid layers of a few nanometres to tens of micrometres thickness that are deposited onto a substrate. So-called structure zone models were developed to describe the microstructure of thin films as a function of the homologous temperature (Th), which is the ratio of deposition temperature to melting temperature. According to these models, a necessary condition for the occurrence of amorphous phases is that (Th) has to be smaller than 0.3. The deposition temperature must be below 30% of the melting temperature. === Superconductivity === Regarding their applications, amorphous metallic layers played an important role in the discovery of superconductivity in amorphous metals made by Buckel and Hilsch. The superconductivity of amorphous metals, including amorphous metallic thin films, is now understood to be due to phonon-mediated Cooper pairing. The role of structural disorder can be rationalized based on the strong-coupling Eliashberg theory of superconductivity. === Thermal


id: sonoluminescence-20260505-0
file: data/en.wikipedia.org/wiki/Sonoluminescence-0.md
category: reference
title: Sonoluminescence
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Sonoluminescence
date_saved: 2026-05-05T11:06:20.444802+00:00
instance: kb-cron
parent: sonoluminescence-20260505-0
summary:
Sonoluminescence is luminescence induced by sound waves, such as in the emission of light from imploding bubbles in a liquid when excited by sound. Sonoluminescence is sometimes considered a kind of mechanoluminescence. However, mechanoluminescence is typically defined as pertaining to solids, while sonoluminescence usually pertains to liquids. The related terms acoustoluminescence and sonotriboluminescence have been used to describe sound-induced luminescence in solids (e.g., crystals suspended in slurries). Sonoluminescence was first discovered in 1934 at the University of Cologne. It occurs when a sound wave of sufficient intensity induces a gaseous cavity within a liquid to collapse quickly, emitting a burst of light. The phenomenon can be observed in stable single-bubble sonoluminescence (SBSL) and multi-bubble sonoluminescence (MBSL). In 1960, Peter Jarman proposed that sonoluminescence is thermal in origin and might arise from microshocks within collapsing cavities. Later experiments revealed that the temperature inside the bubble during SBSL could reach up to 12,000 kelvins (11,700 °C; 21,100 °F). The exact mechanism behind sonoluminescence remains unknown, with various hypotheses including hotspot, bremsstrahlung, and collision-induced radiation. Some researchers have even speculated that temperatures in sonoluminescing systems could reach millions of kelvins, potentially causing thermonuclear fusion; this idea, however, has been met with skepticism by


id: sonoluminescence-20260505-1
file: data/en.wikipedia.org/wiki/Sonoluminescence-1.md
category: reference
title: Sonoluminescence
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Sonoluminescence
date_saved: 2026-05-05T11:06:20.444802+00:00
instance: kb-cron
parent: sonoluminescence-20260505-0
summary:
R R ¨ + 3 2 R ˙ 2 = 1 ρ ( P ∞ ( t ) − P 0 ( t ) − 4 μ R ˙ R − 2 γ R ) {\displaystyle R{\ddot {R}}+{\frac {3}{2}}{\dot {R}}^{2}={\frac {1}{\rho }}\left(P_{\infty }(t)-P_{0}(t)-4\mu {\frac {\dot {R}}{R}}-{\frac {2\gamma }{R}}\right)} This is an approximate equation that is derived from the Navier–Stokes equations (written in spherical coordinate system) and describes the motion of the radius of the bubble R as a function of time t. Here, μ is the viscosity, P ∞ ( t ) {\displaystyle P_{\infty }(t)} is the external pressure infinitely far from the bubble, P 0 ( t ) {\displaystyle P_{0}(t)} is the internal pressure of the bubble, ρ {\displaystyle \rho } is the liquid density, and γ is the surface tension. The over-dots represent time derivatives. This equation, though approximate, has been shown to give good estimates on the motion of the bubble under the acoustically driven field except during the final stages of collapse. Both simulation and experimental measurement show that during the critical final stages of collapse, the bubble wall velocity exceeds the speed of sound of the gas inside the bubble. Thus a more detailed analysis


id: sonoluminescence-20260505-2
file: data/en.wikipedia.org/wiki/Sonoluminescence-2.md
category: reference
title: Sonoluminescence
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Sonoluminescence
date_saved: 2026-05-05T11:06:20.444802+00:00
instance: kb-cron
parent: sonoluminescence-20260505-0
summary:
== Biological sonoluminescence == Pistol shrimp (also called snapping shrimp) produce a type of cavitation luminescence from a collapsing bubble caused by quickly snapping its claw. The animal snaps a specialized claw shut to create a cavitation bubble that generates acoustic pressures of up to 80 kPa at a distance of 4 cm from the claw. As it extends out from the claw, the bubble reaches speeds of 60 miles per hour (97 km/h) and releases a sound reaching 218 decibels. The pressure is strong enough to kill small fish. The light produced is of lower intensity than the light produced by typical sonoluminescence and is not visible to the naked eye. The light and heat produced by the bubble may have no direct significance, as it is the shockwave produced by the rapidly collapsing bubble which these shrimp use to stun or kill prey. However, it is the first known instance of an animal producing light by this effect and was whimsically dubbed "shrimpoluminescence" upon its discovery in 2001. It has subsequently been discovered that another group of crustaceans, the mantis shrimp, contains species whose club-like forelimbs can strike so quickly and with such force as to induce sonoluminescent


id: strange-matter-20260505-0
file: data/en.wikipedia.org/wiki/Strange_matter-0.md
category: reference
title: Strange matter
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Strange_matter
date_saved: 2026-05-05T11:06:21.627423+00:00
instance: kb-cron
parent: strange-matter-20260505-0
summary:
Strange matter (or strange quark matter) is quark matter containing strange quarks. In extreme environments, strange matter is hypothesized to occur in the core of neutron stars, or, more speculatively, as isolated droplets that may vary in size from femtometers (strangelets) to kilometers, as in the hypothetical strange stars. At high enough density, strange matter is expected to be color superconducting. Ordinary matter, also referred to as atomic matter, is composed of atoms, with nearly all matter concentrated in the atomic nuclei. Nuclear matter is a liquid composed of neutrons and protons, and they are themselves composed of up and down quarks. Quark matter is a condensed form of matter composed entirely of quarks. When quark matter does not contain strange quarks, it is sometimes referred to as non-strange quark matter. == Context == In particle physics and astrophysics, the term 'strange matter' is used in two different contexts, one broader and the other more specific and hypothetical: In the broader context, our current understanding of the laws of nature predicts that strange matter could be created when nuclear matter (made of protons and neutrons) is compressed beyond a critical density. At this critical pressure and density, the protons and


id: strangelet-20260505-0
file: data/en.wikipedia.org/wiki/Strangelet-0.md
category: reference
title: Strangelet
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Strangelet
date_saved: 2026-05-05T11:06:22.905505+00:00
instance: kb-cron
parent: strangelet-20260505-0
summary:
A strangelet (pronounced ) is a hypothetical particle consisting of a bound state of roughly equal numbers of up, down, and strange quarks. An equivalent description is that a strangelet is a small fragment of strange matter, small enough to be considered a particle. The size of an object composed of strange matter could, theoretically, range from a few femtometers across (with the mass of a light nucleus) to arbitrarily large. Once the size becomes macroscopic (on the order of meters across), such an object is usually called a strange star. The term "strangelet" originates with Edward Farhi and Robert Jaffe in 1984. It has been theorized that strangelets can convert matter to strange matter on contact. Strangelets have also been suggested as a dark matter candidate. == Theoretical possibility == === Strange matter hypothesis === The known particles with strange quarks are unstable. Because the strange quark is heavier than the up and down quarks, it can spontaneously decay, via the weak interaction, into an up quark, an electron, and an antineutrino. Consequently, particles containing strange quarks, such as the lambda particle, always lose their strangeness, by decaying into lighter particles containing only up and down quarks. However, condensed


id: strangelet-20260505-1
file: data/en.wikipedia.org/wiki/Strangelet-1.md
category: reference
title: Strangelet
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Strangelet
date_saved: 2026-05-05T11:06:22.905505+00:00
instance: kb-cron
parent: strangelet-20260505-0
summary:
=== Accelerator production === At heavy ion accelerators like the Relativistic Heavy Ion Collider (RHIC), nuclei are collided at relativistic speeds, creating strange and antistrange quarks that could conceivably lead to strangelet production. The experimental signature of a strangelet would be its very high ratio of mass to charge, which would cause its trajectory in a magnetic field to be very nearly, but not quite, straight. The STAR collaboration has searched for strangelets produced at the RHIC, but none were found. The Large Hadron Collider (LHC) is even less likely to produce strangelets, but searches are planned for the LHC ALICE detector. === Space-based detection === The Alpha Magnetic Spectrometer (AMS), an instrument that is mounted on the International Space Station, could detect strangelets. === Possible seismic detection === In May 2002, a group of researchers at Southern Methodist University reported the possibility that strangelets may have been responsible for seismic events recorded on 22 October and 24 November 1993. The authors later retracted their claim, after finding that the clock of one of the seismic stations had a large error during the relevant period. It has been suggested that the International Monitoring System be set up to verify the


id: strangelet-20260505-2
file: data/en.wikipedia.org/wiki/Strangelet-2.md
category: reference
title: Strangelet
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Strangelet
date_saved: 2026-05-05T11:06:22.905505+00:00
instance: kb-cron
parent: strangelet-20260505-0
summary:
== In fiction == One episode of the TV series Odyssey 5 featured an attempt to destroy the planet by intentionally creating negatively charged strangelets in a particle accelerator. The BBC docudrama End Day features a scenario where a particle accelerator in New York City explodes. This creates a strangelet which creates a chain reaction which destroys Earth. The Robert L. Forward story "A Matter Most Strange" included ins collection Indistinguishable from Magic deals with the making of a strangelet in a particle accelerator. In Douglas Preston's 2010 novel Impact, an alien machine creates strangelets. The machine's strangelets impact the Earth and Moon and pass through them. Steve Alten's 2011 novel Phobos, written as the third and final part of his Domain trilogy, presents a fictional story where strangelets are unintentionally created at the LHC and escape from it to destroy the Earth. In Donald E. Westlake's 1992 black-comedy novel Humans, an irritated God sends an angel to Earth to bring about Armageddon by means of using a strangelet created in a particle accelerator to convert the Earth into a quark star. In the 2010 film Quantum Apocalypse, a strangelet approaches the Earth from space. In Hannu Rajaniemi's novel The


id: strong-cp-problem-20260505-0
file: data/en.wikipedia.org/wiki/Strong_CP_problem-0.md
category: reference
title: Strong CP problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Strong_CP_problem
date_saved: 2026-05-05T11:06:24.092448+00:00
instance: kb-cron
parent: strong-cp-problem-20260505-0
summary:
The strong CP problem is a question in particle physics, which brings up the following quandary: why does quantum chromodynamics (QCD) seem to preserve CP-symmetry? In particle physics, CP stands for the combination of C-symmetry (charge conjugation symmetry) and P-symmetry (parity symmetry). According to the current mathematical formulation of quantum chromodynamics, a violation of CP-symmetry in strong interactions could occur. However, no violation of the CP-symmetry has ever been seen in any experiment involving only the strong interaction. As there is no known reason in QCD for it to necessarily be conserved, this is a "fine tuning" problem known as the strong CP problem. The strong CP problem is sometimes regarded as an unsolved problem in physics, and has been referred to as "the most underrated puzzle in all of physics." There are several proposed solutions to solve the strong CP problem. The most well-known is Peccei–Quinn theory, involving new pseudoscalar particles called axions. == Theory == CP-symmetry states that physics should be unchanged if particles were swapped with their antiparticles and then left-handed and right-handed particles were also interchanged. This corresponds to performing a charge conjugation transformation and then a parity transformation. The symmetry is known to be broken


id: superconductivity-20260505-0
file: data/en.wikipedia.org/wiki/Superconductivity-0.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T11:06:25.375736+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
Superconductivity is a set of physical properties observed in superconductors: materials where electrical resistance vanishes and magnetic fields are expelled from the material. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered, even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source. The superconductivity phenomenon was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes. Like ferromagnetism and atomic spectral lines, superconductivity is a phenomenon which can only be explained by quantum mechanics. It is characterized by the Meissner effect, the complete cancellation of the magnetic field in the interior of the superconductor during its transitions into the superconducting state. The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics. In 1986, it was discovered that some cuprate-perovskite ceramic materials have a critical temperature above 35 K (−238 °C). It was shortly found (by Ching-Wu Chu) that replacing the lanthanum with yttrium, i.e. making YBCO, raised the critical temperature to 92 K (−181 °C), which was


id: superconductivity-20260505-1
file: data/en.wikipedia.org/wiki/Superconductivity-1.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T11:06:25.375736+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
=== Niobium === The first practical application of superconductivity was developed in 1954 with Dudley Allen Buck's invention of the cryotron. Two superconductors with greatly different values of the critical magnetic field are combined to produce a fast, simple switch for computer elements. Soon after discovering superconductivity in 1911, Kamerlingh Onnes attempted to make an electromagnet with superconducting windings but found that relatively low magnetic fields destroyed superconductivity in the materials he investigated. Much later, in 1955, G. B. Yntema succeeded in constructing a small 0.7-tesla iron-core electromagnet with superconducting niobium wire windings. Then, in 1961, J. E. Kunzler, E. Buehler, F. S. L. Hsu, and J. H. Wernick made the startling discovery that, at 4.2 kelvin, niobium–tin, a compound consisting of three parts niobium and one part tin, was capable of supporting a current density of more than 100,000 amperes per square centimeter in a magnetic field of 8.8 tesla. The alloy was brittle and difficult to fabricate, but niobium–tin proved useful for generating magnetic fields as high as 20 tesla. In 1962, T. G. Berlincourt and R. R. Hake discovered that more ductile alloys of niobium and titanium are suitable for applications up to 10 tesla. Commercial production


id: superconductivity-20260505-2
file: data/en.wikipedia.org/wiki/Superconductivity-2.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T11:06:25.375736+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
=== Theory of operation === A superconductor is conventional if it is driven by electron–phonon interaction and explained by the BCS theory or its extension, the Eliashberg theory. Otherwise, it is unconventional. Alternatively, a superconductor is called unconventional if the superconducting order parameter transforms according to a non-trivial irreducible representation of the system's point group or space group. === Critical temperature === A superconductor is generally considered high-temperature if it reaches a superconducting state above a temperature of 30 K (−243.15 °C); as in the initial discovery by Georg Bednorz and K. Alex Müller. It may also reference materials that transition to superconductivity when cooled using liquid nitrogen – that is, at only Tc > 77 K, although this is generally used only to emphasize that liquid nitrogen coolant is sufficient. Low temperature superconductors refer to materials with a critical temperature below 30 K, and are cooled mainly by liquid helium (Tc > 4.2 K). One exception to this rule is the iron pnictide group of superconductors that display behaviour and properties typical of high-temperature superconductors, yet some of the group have critical temperatures below 30 K. === Material === Superconductor material classes include chemical elements (e.g. mercury or lead),


id: superconductivity-20260505-3
file: data/en.wikipedia.org/wiki/Superconductivity-3.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T11:06:25.375736+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
In superconducting materials, the characteristics of superconductivity appear when the temperature T is lowered below a critical temperature Tc. The value of this critical temperature varies from material to material. Conventional superconductors usually have critical temperatures ranging from around 20 K to less than 1 K. Solid mercury, for example, has a critical temperature of 4.2 K. As of 2015, the highest critical temperature found for a conventional superconductor is 203 K for H2S, although high pressures of approximately 90 gigapascals were required. Cuprate superconductors can have much higher critical temperatures: YBa2Cu3O7, one of the first cuprate superconductors to be discovered, has a critical temperature above 90 K, and mercury-based cuprates have been found with critical temperatures in excess of 130 K. The basic physical mechanism responsible for the high critical temperature is not yet clear. However, it is clear that a two-electron pairing is involved, although the nature of the pairing ( s {\displaystyle s} wave vs. d {\displaystyle d} wave) remains controversial. Similarly, at a fixed temperature below the critical temperature, superconducting materials cease to superconduct when an external magnetic field is applied which is greater than the critical magnetic field. This is because the Gibbs free energy


id: superconductivity-20260505-4
file: data/en.wikipedia.org/wiki/Superconductivity-4.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T11:06:25.375736+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
When a superconductor is placed in a weak external magnetic field Ba=Ha, and cooled below its transition temperature, the magnetic field is ejected. The Meissner effect does not cause the field to be completely ejected but instead, the field penetrates the superconductor but only to a very small distance, characterized by a parameter λ, called the London penetration depth, decaying exponentially to zero within the bulk of the material. The Meissner effect is a defining characteristic of superconductivity. For most superconductors, the London penetration depth is on the order of 100 nm. The Meissner effect is sometimes confused with the kind of diamagnetism one would expect in a perfect electrical conductor: according to Lenz's law, when a changing magnetic field is applied to a conductor, it will induce an electric current in the conductor that creates an opposing magnetic field. In a perfect conductor, an arbitrarily large current can be induced, and the resulting magnetic field exactly cancels the applied field. The Meissner effect is distinct from this – it is the spontaneous expulsion that occurs during transition to superconductivity. Suppose we have a material in its normal state, containing a constant internal magnetic field. When the material is cooled


id: superconductivity-20260505-5
file: data/en.wikipedia.org/wiki/Superconductivity-5.md
category: reference
title: Superconductivity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Superconductivity
date_saved: 2026-05-05T11:06:25.375736+00:00
instance: kb-cron
parent: superconductivity-20260505-0
summary:
Superconductors are promising candidate materials for devising fundamental circuit elements of electronic, spintronic, and quantum technologies. One such example is a superconducting diode, in which supercurrent flows along one direction only, that promise dissipationless superconducting and semiconducting-superconducting hybrid technologies. Superconducting magnets are some of the most powerful electromagnets known. They are used in MRI/NMR machines, mass spectrometers, the beam-steering magnets used in particle accelerators and plasma confining magnets in some tokamaks. They can also be used for magnetic separation, where weakly magnetic particles are extracted from a background of less or non-magnetic particles, as in the pigment industries. They can also be used in large wind turbines to overcome the restrictions imposed by high electrical currents, with an industrial grade 3.6 megawatt superconducting windmill generator having been tested successfully in Denmark. In the 1950s and 1960s, superconductors were used to build experimental digital computers using cryotron switches. More recently, superconductors have been used to make digital circuits based on rapid single flux quantum technology and RF and microwave filters for mobile phone base stations. Superconductors are used to build Josephson junctions which are the building blocks of SQUIDs (superconducting quantum interference devices), the most sensitive magnetometers known. SQUIDs are used


id: time-perception-20260505-0
file: data/en.wikipedia.org/wiki/Time_perception-0.md
category: reference
title: Time perception
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_perception
date_saved: 2026-05-05T11:06:26.691763+00:00
instance: kb-cron
parent: time-perception-20260505-0
summary:
In psychology and neuroscience, time perception or chronoception is the subjective experience, or sense, of time, which is measured by someone's own perception of the duration of the indefinite and unfolding of events. The perceived time interval between two successive events is referred to as perceived duration. Though directly experiencing or understanding another person's perception of time is not possible, perception can be objectively studied and inferred through a number of scientific experiments. Some temporal illusions help to expose the underlying neural mechanisms of time perception. The ancient Greeks recognized the difference between chronological time (chronos) and subjective time (kairos). Pioneering work on time perception, emphasizing species-specific differences, was conducted by Karl Ernst von Baer. == Theories == Time perception is typically categorized in five distinct ranges, because different ranges of duration are processed in different areas of the brain: Sub-second timing or millisecond timing Interval timing or seconds-to-minutes timing Circadian timing Astrocyte glutamine clearance delay Mitochondrial hysteresis There are many theories and computational models for time perception mechanisms in the brain. William J. Friedman (1993) contrasted two theories of the sense of time: The strength model of time memory. This posits a memory trace that persists over time, by


id: time-perception-20260505-1
file: data/en.wikipedia.org/wiki/Time_perception-1.md
category: reference
title: Time perception
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_perception
date_saved: 2026-05-05T11:06:26.691763+00:00
instance: kb-cron
parent: time-perception-20260505-0
summary:
if the visual brain wants to get events correct timewise, it may have only one choice: wait for the slowest information to arrive. To accomplish this, it must wait about a tenth of a second. In the early days of television broadcasting, engineers worried about the problem of keeping audio and video signals synchronized. Then they accidentally discovered that they had around a hundred milliseconds of slop: As long as the signals arrived within this window, viewers' brains would automatically resynchronize the signals. He goes on to say, "This brief waiting period allows the visual system to discount the various delays imposed by the early stages; however, it has the disadvantage of pushing perception into the past. There is a distinct survival advantage to operating as close to the present as possible; an animal does not want to live too far in the past. Therefore, the tenth-of-a-second window may be the smallest delay that allows higher areas of the brain to account for the delays created in the first stages of the system while still operating near the border of the present. This window of delay means that awareness is retroactive, incorporating data from a window of time after an


id: time-perception-20260505-2
file: data/en.wikipedia.org/wiki/Time_perception-2.md
category: reference
title: Time perception
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_perception
date_saved: 2026-05-05T11:06:26.691763+00:00
instance: kb-cron
parent: time-perception-20260505-0
summary:
When returning to the hive with nectar, forager honey bees need to know the current ratio of nectar-collecting to nectar-processing rates in the colony. To do so, they estimate the time it takes them to find a food-storer bee, which will unload the forage and store it. The longer it takes them to find one, the busier the food-storer bees are, and therefore the higher the nectar-collecting rate of the colony. Forager bees also assess the quality of nectar by comparing the length of time it takes to unload the forage: a longer unloading time indicates higher quality nectar. They compare their own unloading time to the unloading time of other foragers present in the hive, and adjust their recruiting behavior accordingly. For instance, honey bees reduce the duration of their waggle dance if they judge their own yield to be inferior. Scientists have demonstrated that anesthesia disrupts the circadian clock and impairs the time perception of honey bees, as observed in humans. Experiments revealed that a six-hour-long general anesthesia significantly delayed the start of the foraging behaviour of honeybees if induced during daytime, but not if induced during nighttime. Bumble bees can be successfully trained to respond to a


id: time-perception-20260505-3
file: data/en.wikipedia.org/wiki/Time_perception-3.md
category: reference
title: Time perception
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_perception
date_saved: 2026-05-05T11:06:26.691763+00:00
instance: kb-cron
parent: time-perception-20260505-0
summary:
In an experiment, participants were told to stare at an "x" symbol on a computer screen whereby a moving blue doughnut-like ring repeatedly circled the fixed "x" point. Occasionally, the ring would display a white flash for a split second that physically overlapped the ring's interior. However, when asked what was perceived, participants responded that they saw the white flash lagging behind the center of the moving ring. In other words, despite the reality that the two retinal images were actually spatially aligned, the flashed object was usually observed to trail a continuously moving object in space — a phenomenon referred to as the flash-lag effect. The first proposed explanation, called the "motion extrapolation" hypothesis, is that the visual system extrapolates the position of moving objects but not flashing objects when accounting for neural delays (i.e., the lag time between the retinal image and the observer's perception of the flashing object). The second proposed explanation by David Eagleman and Sejnowski, called the "latency difference" hypothesis, is that the visual system processes moving objects at a faster rate than flashed objects. In the attempt to disprove the first hypothesis, David Eagleman conducted an experiment in which the moving ring suddenly reverses


id: time-perception-20260505-4
file: data/en.wikipedia.org/wiki/Time_perception-4.md
category: reference
title: Time perception
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_perception
date_saved: 2026-05-05T11:06:26.691763+00:00
instance: kb-cron
parent: time-perception-20260505-0
summary:
==== Awe ==== Research has suggested the feeling of awe has the ability to expand one's perceptions of time availability. Awe can be characterized as an experience of immense perceptual vastness that coincides with an increase in focus. Consequently, it is conceivable that one's temporal perception would slow down when experiencing awe. The perception of time can differ as people choose between savoring moments and deferring gratification. ==== Fear ==== Possibly related to the oddball effect, research suggests that time seems to slow down for a person during dangerous events (such as a car accident, a robbery, or when a person perceives a potential predator or mate), or when a person skydives or bungee jumps, where they are capable of complex thoughts in what would normally be the blink of an eye (e.g., a fight-or-flight response). This reported slowing in temporal perception may have been evolutionarily advantageous because it may have enhanced one's ability to intelligibly make quick decisions in moments that were of critical importance to survival. However, even though observers commonly report that time seems to have moved in slow motion during these events, it is unclear whether this is a function of increased time resolution during the


id: time-perception-20260505-5
file: data/en.wikipedia.org/wiki/Time_perception-5.md
category: reference
title: Time perception
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_perception
date_saved: 2026-05-05T11:06:26.691763+00:00
instance: kb-cron
parent: time-perception-20260505-0
summary:
When solved, S 2 − S 1 = K ( log ⁡ R 2 − log ⁡ R 1 ) = K log ⁡ ( R 2 / R 1 ) {\displaystyle S_{2}-S_{1}=K(\log {R_{2}}-\log {R_{1}})=K\log {\left({R_{2}}/{R_{1}}\right)}} . One day would be approximately 1/4,000 of the life of an 11-year-old, but approximately 1/20,000 of the life of a 55-year-old. So a year would be experienced by a 55-year-old as passing approximately five times more quickly than a year experienced by an 11-year-old. If long-term time perception is based solely on the proportionality of a person's age, then the following four periods in life would appear to be quantitatively equal: ages 5–10 (1x), ages 10–20 (2x), ages 20–40 (4x), age 40–80 (8x), as the end age is twice the start age. However, this does not work for ages 0–10, which corresponds to ages 10–∞. ==== Proportional to the subjective time ==== Lemlich posits that the passage of subjective time relative to actual time is inversely proportional to total subjective time, rather than the total real time: d S d R = K S {\displaystyle {\frac {dS}{dR}}={\frac {K}{S}}} When mathematically solved, S 2 = 2 K R + C {\displaystyle S^{2}=2KR+C} It avoids


id: time-perception-20260505-6
file: data/en.wikipedia.org/wiki/Time_perception-6.md
category: reference
title: Time perception
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Time_perception
date_saved: 2026-05-05T11:06:26.691763+00:00
instance: kb-cron
parent: time-perception-20260505-0
summary:
== Time perception and artificial intelligence == Time perception refers to the ability to represent, estimate, and use temporal information. While it is a fundamental aspect of biological cognition, recent research has increasingly sought to model temporal processing in artificial systems, especially embodied artificial systems. This line of research has been suggested to be crucial for human-robot interaction, where understanding subtle timing cues can improve coordination and collaboration. For example, timing precision also affects user satisfaction, as temporal accuracy in robotic movements often matters more than spatial precision. Computational studies of biological timing mechanisms also help generate testable hypotheses about biological time perception. Consequently, computational and robotic models have been developed to simulate various timing abilities, such as duration estimation, interval reproduction, and temporal prediction, across cognitive and emergent modelling frameworks. Many of these models use neural network dynamics, oscillatory systems, or reinforcement learning to produce clock-like timing without an explicit clock structure. == Applications in urban design == Beyond laboratory settings, time perception has also been studied in relation to the design of urban environments. In this context, Shakibamanesh and Ghorbanian (2017) developed an applied time-based evaluation checklist that enables urban designers to systematically analyze how spatial form, visual


id: tunguska-event-20260505-0
file: data/en.wikipedia.org/wiki/Tunguska_event-0.md
category: reference
title: Tunguska event
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tunguska_event
date_saved: 2026-05-05T11:06:27.907118+00:00
instance: kb-cron
parent: tunguska-event-20260505-0
summary:
The Tunguska event was a large explosion of between 3–50 megatons TNT equivalent that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of 30 June [O.S. 17 June] 1908. The explosion over the sparsely populated East Siberian taiga felled a large number of trees, over an area of 2,150 km2 (830 sq mi) of forest, and eyewitness accounts suggest up to three people may have died. The explosion is attributed to a meteor air burst, the atmospheric explosion of a stony asteroid about 50–60 m (160–200 ft) wide. The asteroid approached from the east-south-east, probably with a relatively high speed of about 27 km/s; 98,004 km/h (Mach 80). Though the incident is classified as an impact event, the object is thought to have exploded at an altitude of 5–10 km (3–6 mi) rather than hitting the Earth's surface, leaving no impact crater. The Tunguska event is the largest impact event on Earth in recorded history, though much larger impacts are believed to have occurred in prehistoric times, including the Chicxulub impact that ended the Cretaceous period. An explosion of the Tunguska magnitude would be capable of destroying a large metropolitan area. The


id: tunguska-event-20260505-1
file: data/en.wikipedia.org/wiki/Tunguska_event-1.md
category: reference
title: Tunguska event
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tunguska_event
date_saved: 2026-05-05T11:06:27.907118+00:00
instance: kb-cron
parent: tunguska-event-20260505-0
summary:
We had a hut by the river with my brother Chekaren. We were sleeping. Suddenly we both woke up at the same time. Somebody shoved us. We heard whistling and felt strong wind. Chekaren said "Can you hear all those birds flying overhead?" We were both in the hut, couldn't see what was going on outside. Suddenly, I got shoved again, this time so hard I fell into the fire. I got scared. Chekaren got scared too. We started crying out for father, mother, brother, but no one answered. There was noise beyond the hut, we could hear trees falling down. Chekaren and I got out of our sleeping bags and wanted to run out, but then the thunder struck. This was the first thunder. The Earth began to move and rock, the wind hit our hut and knocked it over. My body was pushed down by sticks, but my head was in the clear. Then I saw a wonder: trees were falling, the branches were on fire, it became mighty bright, how can I say this, as if there was a second sun, my eyes were hurting, I even closed them. It was like what the Russians call lightning.


id: tunguska-event-20260505-2
file: data/en.wikipedia.org/wiki/Tunguska_event-2.md
category: reference
title: Tunguska event
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tunguska_event
date_saved: 2026-05-05T11:06:27.907118+00:00
instance: kb-cron
parent: tunguska-event-20260505-0
summary:
== Scientific investigation == Since the 1908 event, an estimated 1,000 scholarly papers (most in Russian) have been published about the Tunguska explosion. Owing to the site's remoteness and the limited instrumentation available at the time of the event, modern scientific interpretations of its cause and magnitude have relied chiefly on damage assessments and geological studies conducted many years after the event. Estimates of its energy have ranged from 3–30 megatons of TNT (13–126 PJ). Not until more than a decade after the event did any scientific analysis of the region take place, in part due to the area's isolation and significant political upheaval affecting Russia in the 1910s. In 1921, the Russian mineralogist Leonid Kulik led a team to the Podkamennaya Tunguska River basin to conduct a survey for the Soviet Academy of Sciences. Although they never visited the central blast area, the many local accounts of the event led Kulik to believe that a giant meteorite impact had caused the event. Upon returning, he persuaded the Soviet government to fund an expedition to the suspected impact zone, based on the prospect of salvaging meteoric iron. Kulik led a scientific expedition to the Tunguska blast site in 1927. He


id: tunguska-event-20260505-3
file: data/en.wikipedia.org/wiki/Tunguska_event-3.md
category: reference
title: Tunguska event
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tunguska_event
date_saved: 2026-05-05T11:06:27.907118+00:00
instance: kb-cron
parent: tunguska-event-20260505-0
summary:
Researcher John Anfinogenov has suggested that a boulder found at the event site, known as "John's stone", is a remnant of the meteorite, but oxygen isotope analysis of the quartzite suggests that it is of hydrothermal origin, and probably related to Permian-Triassic Siberian Traps magmatism. In 2013, a team of researchers published the results of an analysis of micro-samples from a peat bog near the centre of the affected area, which show fragments that may be of extraterrestrial origin. Although it is widely claimed the impact resulted in the felling of over 80 million trees, this was based on a preliminary guess multiplying tree density by impacted area that overestimated the area of devastation by a factor of four, so is likely to be incorrect. The largest accurately recorded felled trees are around 44 cm (17 in) in trunk diameter and not around 1 m (3.3 ft) that has been claimed by some sources. The observations of decreased atmospheric transparency at the Mount Wilson Observatory in California have been used to calculate that roughly a million tons of dust were released into the stratosphere. Further modelling suggests that shock waves from the falling meteor generated up to 30 Mt of


id: tunguska-event-20260505-4
file: data/en.wikipedia.org/wiki/Tunguska_event-4.md
category: reference
title: Tunguska event
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tunguska_event
date_saved: 2026-05-05T11:06:27.907118+00:00
instance: kb-cron
parent: tunguska-event-20260505-0
summary:
==== Asteroid or comet ==== In 1930, the British meteorologist and mathematician F. J. W. Whipple suggested that the Tunguska body was a small comet. A comet is composed of dust and volatiles, such as water ice and frozen gases, and could have been completely vaporised by the impact with Earth's atmosphere, leaving no obvious traces. The comet hypothesis was further supported by the glowing skies (or "skyglows" or "bright nights") observed across Eurasia for several evenings after the impact, which are possibly explained by dust and ice that had been dispersed from the comet's tail across the upper atmosphere. The cometary hypothesis gained a general acceptance among Soviet Tunguska investigators by the 1960s. In 1978, Slovak astronomer Ľubor Kresák suggested that the body was a fragment of Comet Encke, a periodic comet with a period of just over three years that stays entirely within Jupiter's orbit. It is also responsible for the Beta Taurids, an annual meteor shower with a maximum activity around 28–29 June. The Tunguska event coincided with that shower's peak activity, the Tunguska object's approximate trajectory is consistent with what would be expected from a fragment of Comet Encke, and a hypothetical risk corridor has now


id: tunguska-event-20260505-5
file: data/en.wikipedia.org/wiki/Tunguska_event-5.md
category: reference
title: Tunguska event
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tunguska_event
date_saved: 2026-05-05T11:06:27.907118+00:00
instance: kb-cron
parent: tunguska-event-20260505-0
summary:
==== Chelyabinsk meteor ==== The February 2013 Chelyabinsk bolide event provided ample data for scientists to create new models for the Tunguska event. Researchers used data from both Tunguska and Chelyabinsk to perform a statistical study of over 50 million combinations of bolide and entry properties that could produce Tunguska-scale damage when breaking apart or exploding at similar altitudes. Some models focused on combinations of properties which created scenarios with similar effects to the tree-fall pattern as well as the atmospheric and seismic pressure waves of Tunguska. Four different computer models produced similar results; they concluded that the likeliest candidate for the Tunguska impactor was a stony body between 50–80 m (164–262 ft) in diameter, entering the atmosphere at roughly 55,000 km/h (34,000 mph), exploding at 10–14 km (6–9 mi) altitude, and releasing explosive energy equivalent to between 10–30 megatons. This is similar to the blast energy equivalent of the 1980 volcanic eruption of Mount St. Helens. The researchers also concluded impactors of this size hit the Earth only at an average interval scale of millennia. ==== Lake Cheko ==== In June 2007, scientists from the University of Bologna identified a lake in the Tunguska region as a possible impact


id: tunguska-event-20260505-6
file: data/en.wikipedia.org/wiki/Tunguska_event-6.md
category: reference
title: Tunguska event
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tunguska_event
date_saved: 2026-05-05T11:06:27.907118+00:00
instance: kb-cron
parent: tunguska-event-20260505-0
summary:
=== Geophysical hypotheses === Though scientific consensus is that the Tunguska explosion was caused by the impact of a small asteroid, there are some dissenters. Astrophysicist Wolfgang Kundt has proposed that the Tunguska event was caused by the release and subsequent explosion of 10 million tons of natural gas from within the Earth's crust. The basic idea is that natural gas leaked out of the crust and then rose to its equal-density height in the atmosphere; from there, it drifted downwind, in a sort of wick, which eventually found an ignition source such as lightning. Once the gas was ignited, the fire streaked along the wick, and then down to the source of the leak in the ground, whereupon there was an explosion. The similar verneshot hypothesis has also been proposed as a possible cause of the Tunguska event. Other research has proposed a geophysical mechanism for the event. == Similar event == A smaller air burst occurred over a populated area on 15 February 2013, at Chelyabinsk in the Ural district of Russia. The exploding meteoroid was determined to have been an asteroid that measured about 17–20 m (56–66 ft) across. It had an estimated initial mass of 11,000


id: unified-field-theory-20260505-0
file: data/en.wikipedia.org/wiki/Unified_field_theory-0.md
category: reference
title: Unified field theory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Unified_field_theory
date_saved: 2026-05-05T11:06:29.038086+00:00
instance: kb-cron
parent: unified-field-theory-20260505-0
summary:
In physics, a Unified Field Theory (UFT) is a type of field theory that allows all fundamental forces of nature, including gravity, and all elementary particles to be written in terms of a single physical field. According to quantum field theory, particles are themselves the quanta of fields. Different fields in physics include vector fields such as the electromagnetic field, spinor fields whose quanta are fermionic particles such as electrons, and tensor fields such as the metric tensor field that describes the shape of spacetime and gives rise to gravitation in general relativity. Unified field theories attempt to organize these fields into a single mathematical structure. For over a century, the unified field theory has remained an open line of research. The term was coined by Albert Einstein, who attempted to unify his general theory of relativity with electromagnetism. Einstein attempted to create a classical unified field theory. Among other difficulties, this required a new explanation of particles as singularities or solitons instead of field quanta. Later attempts to unify general relativity with other forces incorporate quantum mechanics. The concept of a "Theory of Everything" or Grand Unified Theory are closely related to unified field theory. A theory of everything


id: unified-field-theory-20260505-1
file: data/en.wikipedia.org/wiki/Unified_field_theory-1.md
category: reference
title: Unified field theory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Unified_field_theory
date_saved: 2026-05-05T11:06:29.038086+00:00
instance: kb-cron
parent: unified-field-theory-20260505-0
summary:
=== Modern progress === In 1963, American physicist Sheldon Glashow proposed that the weak nuclear force, electricity, and magnetism could arise from a partially unified electroweak theory. In 1967, Pakistani Abdus Salam and American Steven Weinberg independently revised Glashow's theory by having the masses for the W particle and Z particle arise through spontaneous symmetry breaking with the Higgs mechanism. This unified theory modelled the electroweak interaction as a force mediated by four particles: the photon for the electromagnetic aspect, a neutral Z particle, and two charged W particles for the weak aspect. As a result of the spontaneous symmetry breaking, the weak force becomes short-range and the W and Z bosons acquire masses of 80.4 and 91.2 GeV/c2, respectively. Their theory was first given experimental support by the discovery of weak neutral currents in 1973. In 1983, the Z and W bosons were first produced at CERN by Carlo Rubbia's team. For their insights, Glashow, Salam, and Weinberg were awarded the Nobel Prize in Physics in 1979. Carlo Rubbia and Simon van der Meer received the Prize in 1984. After Gerardus 't Hooft showed the Glashow–Weinberg–Salam electroweak interactions to be mathematically consistent, the electroweak theory became a template for


id: yang-mills-existence-and-mass-gap-20260505-0
file: data/en.wikipedia.org/wiki/Yang–Mills_existence_and_mass_gap-0.md
category: reference
title: Yang–Mills existence and mass gap
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Yang–Mills_existence_and_mass_gap
date_saved: 2026-05-05T11:06:30.271614+00:00
instance: kb-cron
parent: yang-mills-existence-and-mass-gap-20260505-0
summary:
The Yang–Mills existence and mass gap problem is an unsolved problem in mathematical physics and mathematics, and one of the seven Millennium Prize Problems defined by the Clay Mathematics Institute, which has offered a prize of US$1,000,000 for its solution. The problem is phrased as follows: Yang–Mills Existence and Mass Gap. Prove that for any compact simple gauge group G, a non-trivial quantum Yang–Mills theory exists on R 4 {\displaystyle \mathbb {R} ^{4}} and has a mass gap Δ > 0. Existence includes establishing axiomatic properties at least as strong as those cited in Streater & Wightman (1964), Osterwalder & Schrader (1973) and Osterwalder & Schrader (1975) [citations adapted]. In this statement, a quantum Yang–Mills theory is a non-abelian quantum field theory similar to that underlying the Standard Model of particle physics; R 4 {\displaystyle \mathbb {R} ^{4}} is Euclidean 4-space; the mass gap Δ is the mass of the least massive particle predicted by the theory. Therefore, the winner must prove that: Yang–Mills theory exists and satisfies the standard of rigor that characterizes contemporary mathematical physics, in particular constructive quantum field theory, and The mass of all particles of the force field predicted by the theory are strictly positive.


id: yang-mills-existence-and-mass-gap-20260505-1
file: data/en.wikipedia.org/wiki/Yang–Mills_existence_and_mass_gap-1.md
category: reference
title: Yang–Mills existence and mass gap
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Yang–Mills_existence_and_mass_gap
date_saved: 2026-05-05T11:06:30.271614+00:00
instance: kb-cron
parent: yang-mills-existence-and-mass-gap-20260505-0
summary:
⟨ ϕ ( 0 , t ) ϕ ( 0 , 0 ) ⟩ ∼ ∑ n A n exp ⁡ ( − Δ n t ) {\displaystyle \langle \phi (0,t)\phi (0,0)\rangle \sim \sum _{n}A_{n}\exp \left(-\Delta _{n}t\right)} with Δ 0 > 0 {\displaystyle \Delta _{0}>0} being the lowest energy value in the spectrum of the Hamiltonian and thus the mass gap. This quantity, easy to generalize to other fields, is what is generally measured in lattice computations. It was proved in this way that Yang–Mills theory develops a mass gap on a lattice. == Importance of Yang–Mills theory == Most known and nontrivial (i.e. interacting) quantum field theories in 4 dimensions are effective field theories with a cutoff scale. Since the beta function is positive for most models, it appears that most such models have a Landau pole as it is not at all clear whether or not they have nontrivial UV fixed points. This means that if such a QFT is well-defined at all scales, as it has to be to satisfy the axioms of axiomatic quantum field theory, it would have to be trivial (i.e. a free field theory). Quantum Yang–Mills theory with a non-abelian gauge group and


id: list-of-quantum-computing-journals-20260505-0
file: data/en.wikipedia.org/wiki/List_of_quantum_computing_journals-0.md
category: reference
title: List of quantum computing journals
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/List_of_quantum_computing_journals
date_saved: 2026-05-05T11:06:31.825492+00:00
instance: kb-cron
parent: list-of-quantum-computing-journals-20260505-0
summary:
This is a list of quantum computing journals which is a collection of peer-reviewed scientific journals that publish research in the field of quantum computing, including topics such as quantum algorithms, quantum information theory, quantum cryptography, and quantum hardware. == Journals == Quantum (journal) npj Quantum Information Quantum Information Processing International Journal of Quantum Information Entropy (journal) Physical Review A New Journal of Physics Nature Physics Nature Communications == See also == List of computer science journals List of physics journals List of scientific journals List of cryptography journals List of computer science conferences Quantum information science Quantum Computation and Quantum Information — textbook Quantum engineering Quantum programming List of quantum algorithms Glossary of quantum computing


id: adiabatic-quantum-computation-20260505-0
file: data/en.wikipedia.org/wiki/Adiabatic_quantum_computation-0.md
category: reference
title: Adiabatic quantum computation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_quantum_computation
date_saved: 2026-05-05T11:06:32.974566+00:00
instance: kb-cron
parent: adiabatic-quantum-computation-20260505-0
summary:
Adiabatic quantum computation (AQC) is a form of quantum computing which relies on the adiabatic theorem to perform calculations and is closely related to quantum annealing. == Description == First, a (potentially complicated) Hamiltonian is found whose ground state describes the solution to the problem of interest. Next, a system with a simple Hamiltonian is prepared and initialized to the ground state. Finally, the simple Hamiltonian is adiabatically evolved to the desired complicated Hamiltonian. By the adiabatic theorem, the system remains in the ground state, so at the end, the state of the system describes the solution to the problem. Adiabatic quantum computing has been shown to be polynomially equivalent to conventional quantum computing in the circuit model. The time complexity for an adiabatic algorithm is the time taken to complete the adiabatic evolution which is dependent on the gap in the energy eigenvalues (spectral gap) of the Hamiltonian. Specifically, if the system is to be kept in the ground state, the energy gap between the ground state and the first excited state of H ( t ) {\displaystyle H(t)} provides an upper bound on the rate at which the Hamiltonian can be evolved at time t {\displaystyle t} .


id: adiabatic-quantum-computation-20260505-1
file: data/en.wikipedia.org/wiki/Adiabatic_quantum_computation-1.md
category: reference
title: Adiabatic quantum computation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Adiabatic_quantum_computation
date_saved: 2026-05-05T11:06:32.974566+00:00
instance: kb-cron
parent: adiabatic-quantum-computation-20260505-0
summary:
H ~ ( s ) = ( 1 − s ) H B + s H P {\displaystyle {\tilde {H}}(s)=(1-s)H_{B}+sH_{P}} , which is the adiabatic evolution Hamiltonian of the algorithm. In accordance with the adiabatic theorem, start from the ground state of Hamiltonian H B {\displaystyle H_{B}} at the beginning, proceed through an adiabatic process, and end in the ground state of problem Hamiltonian H P {\displaystyle H_{P}} . Then measure the z-component of each of the n spins in the final state. This will produce a string z 1 , z 2 , … , z n {\displaystyle z_{1},z_{2},\dots ,z_{n}} which is highly likely to be the result of the satisfiability problem. The run time T must be sufficiently long to assure correctness of the result. According to the adiabatic theorem, T is about ε / g m i n 2 {\displaystyle \varepsilon /g_{\mathrm {min} }^{2}} , where g m i n = min 0 ≤ s ≤ 1 ( E 1 ( s ) − E 0 ( s ) ) {\displaystyle g_{\mathrm {min} }=\min _{0\leq s\leq 1}(E_{1}(s)-E_{0}(s))} is the minimum energy gap between ground state and first excited state. == Comparison to gate-based quantum computing == Adiabatic


id: algorithmic-qubits-20260505-0
file: data/en.wikipedia.org/wiki/Algorithmic_qubits-0.md
category: reference
title: Algorithmic qubits
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Algorithmic_qubits
date_saved: 2026-05-05T11:06:34.178639+00:00
instance: kb-cron
parent: algorithmic-qubits-20260505-0
summary:
Algorithmic Qubits (AQ) are an application based benchmark of quantum computers. Introduced by IonQ in 2020, the goal was to define a "single number figure of merit to evaluate the performance of quantum computers for solving a representative set of quantum algorithms." While other benchmarks such as IBM's Quantum volume are run on random quantum circuits that do not necessarily have practical applications, AQ is measured on specific algorithms which are known to have value by industry, such as those defined by the Quantum Economic Development Consortium. [1] == Definition == IonQ published code for calculating AQ in a Git code repository. [2] The formal definition of calculating AQ is composed of several steps: Let the set of circuits in the benchmark suite be denoted by C. Locate each circuit c ∈ C as a point on the 2D plot by its Width, wc (Number of qubits), and Depth, dc (Number of Controlled NOT (CX) gates) Define success probability for a Quantum circuit c, Fc The circuit passes if Fc - ϵc > t, where ϵc is the statistical error based on the number of shots, ϵ c = √ ( F c ( q − F c ) )


id: amaravati-quantum-valley-20260505-0
file: data/en.wikipedia.org/wiki/Amaravati_Quantum_Valley-0.md
category: reference
title: Amaravati Quantum Valley
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Amaravati_Quantum_Valley
date_saved: 2026-05-05T11:06:35.480296+00:00
instance: kb-cron
parent: amaravati-quantum-valley-20260505-0
summary:
Amaravati Quantum Valley is a planned quantum technology park and hub dedicated for innovations and researches in the field of quantum computing and technologies in India. It is located in Amaravati city of Andhra Pradesh state in India. It is planned that the quantum technology hub will attract huge investments of worth 1 billion USD dollar. It is alignment with the goals of the National Quantum Mission to increase productivity and create wealth through the advanced technologies going to be developed from the Amaravati Quantum Valley. The foreign company IBM and the Indian company Tata Consultancy Services have planned to establish India’s largest quantum computer at the tech park of the Amaravati Quantum Valley, featuring a 156-qubit IBM Heron processor. The planned Amaravati Quantum Valley is seen as a historic opportunity for the state of Andhra Pradesh to become a global hub for the future advanced quantum technologies. It is also considered as the first dedicated "Quantum Valley" tech park in the region of Southern asia. == History == In the March month of 2025, the Government of Andhra Pradesh planned to establish Quantum Valley in the capital city Amaravati as part of National Quantum Mission in India. On 4


id: bacon-shor-code-20260505-0
file: data/en.wikipedia.org/wiki/Bacon–Shor_code-0.md
category: reference
title: Bacon–Shor code
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Bacon–Shor_code
date_saved: 2026-05-05T11:06:36.713955+00:00
instance: kb-cron
parent: bacon-shor-code-20260505-0
summary:
The Bacon–Shor code is a subsystem error correcting code. In a subsystem code, information is encoded in a subsystem of a Hilbert space. Subsystem codes lend to simplified error correcting procedures unlike codes which encode information in the subspace of a Hilbert space. This simplicity led to the first claim of fault tolerant circuit demonstration on a quantum computer. It is named after Dave Bacon and Peter Shor. Given the stabilizer generators of Shor's code: ⟨ X 0 X 1 X 2 X 3 X 4 X 5 , X 0 X 1 X 2 X 6 X 7 X 8 , Z 0 Z 1 , Z 1 Z 2 , Z 3 Z 4 , Z 4 Z 5 , Z 6 Z 7 , Z 7 Z 8 ⟩ {\displaystyle \langle X_{0}X_{1}X_{2}X_{3}X_{4}X_{5},X_{0}X_{1}X_{2}X_{6}X_{7}X_{8},Z_{0}Z_{1},Z_{1}Z_{2},Z_{3}Z_{4},Z_{4}Z_{5},Z_{6}Z_{7},Z_{7}Z_{8}\rangle } , 4 stabilizers can be removed from this generator by recognizing gauge symmetries in the code to get: ⟨ X 0 X 1 X 2 X 3 X 4 X 5 , X 0 X 1 X 2 X 6 X 7 X 8 , Z 0 Z 1 Z 3 Z 4 Z 6 Z 7 , Z 1 Z 2 Z 4


id: stefanie-barz-20260505-0
file: data/en.wikipedia.org/wiki/Stefanie_Barz-0.md
category: reference
title: Stefanie Barz
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Stefanie_Barz
date_saved: 2026-05-05T11:06:37.846175+00:00
instance: kb-cron
parent: stefanie-barz-20260505-0
summary:
Stefanie Barz is a German physicist and Professor of Quantum Information and Technology at the University of Stuttgart working in the field of photonic quantum technology. == Early life and education == Barz studied at the Johannes Gutenberg University Mainz, with a stay at the KTH Royal Institute of Technology within the Erasmus Programme. She earned her PhD from the University of Vienna under the supervision of Anton Zeilinger, working on various aspects of photonic quantum computing, including 'blind' quantum computing using entangled photons, where the sender knows the initial state of entanglement while companies in control of data processing do not, making it impossible for them to decode the information without destroying it. For her dissertation she was awarded the Laudimaxima Prize of the University of Vienna, and her work has been featured in New Scientist and covered by the BBC and NBC. In 2013 Barz was awarded the Maria Schaumayer Prize and the Loschmidt Prize. From 2014 to 2017, Barz was a Marie Skłodowska-Curie Fellow as well as a Millard and Lee Alexander Fellow in the Christ Church College at the University of Oxford. She worked with Ian Walmsley on three-photon interference, during which project she created integrated


id: paul-benioff-20260505-0
file: data/en.wikipedia.org/wiki/Paul_Benioff-0.md
category: reference
title: Paul Benioff
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Paul_Benioff
date_saved: 2026-05-05T11:06:40.105692+00:00
instance: kb-cron
parent: paul-benioff-20260505-0
summary:
Paul Anthony Benioff (May 1, 1930 – March 29, 2022) was an American physicist who helped pioneer the field of quantum computing. Benioff was best known for his research in quantum information theory during the 1970s and 80s that demonstrated the theoretical possibility of quantum computers by describing the first quantum mechanical model of a computer. In this work, Benioff showed that a computer could operate under the laws of quantum mechanics by describing a Schrödinger equation description of Turing machines. Benioff's body of work in quantum information theory encompassed quantum computers, quantum robots, and the relationship between foundations in logic, math, and physics. == Early life and education == Benioff was born on May 1, 1930, in Pasadena, California. His father, Hugo Benioff, was a professor of seismology at the California Institute of Technology, and his mother, Alice Pauline Silverman, received a master's degree in English from the University of California, Berkeley. Benioff also attended Berkeley, where he earned an undergraduate degree in botany in 1951. After a two-year stint working in nuclear chemistry for Tracerlab, he returned to Berkeley. In 1959, he obtained his PhD in nuclear chemistry. == Career and later life == In 1960, Benioff spent


id: paul-benioff-20260505-1
file: data/en.wikipedia.org/wiki/Paul_Benioff-1.md
category: reference
title: Paul Benioff
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Paul_Benioff
date_saved: 2026-05-05T11:06:40.105692+00:00
instance: kb-cron
parent: paul-benioff-20260505-0
summary:
== Selected scientific works == ”Cosmic-ray production rate and mean removal time of beryllium-7 from the atmosphere," Physical Review, Vol. 104, 1956, pp. 1122–1130. ”Information theory in quantum statistical mechanics," Physics Letters, Vol. 14, 1965, pp. 196–197. ”Some aspects of the relationship between mathematical logic and physics. I," Journal of Mathematical Physics, Vol. 11, 1970, pp. 2553–2569. ”Some aspects of the relationship between mathematical logic and physics. II," Journal of Mathematical Physics, Vol. 12, 1971, pp. 360–376. ”Operator valued measures in quantum mechanics: finite and infinite processes," Journal of Mathematical Physics, Vol. 13, 1972, pp. 231–242. ”Decision procedures in quantum mechanics," Journal of Mathematical Physics, Vol. 13, 1972, pp. 908–915. ”Procedures in quantum mechanics without Von Neumann's projection axiom," Journal of Mathematical Physics, Vol. 13, 1972, pp. 1347–1355. ”Some consequences of the strengthened interpretative rules of quantum mechanics," Journal of Mathematical Physics, Vol. 15, 1974, pp. 552–559. ”Models of Zermelo Frankel set theory as carriers for the mathematics of physics. I", Journal of Mathematical Physics, Vol. 17, 1976, pp. 618–628. ”Models of Zermelo Frankel set theory as carriers for the mathematics of physics. II," Journal of Mathematical Physics, Vol. 17, 1976, pp. 629–640. ”Finite and infinite measurement sequences in quantum


id: bqp-20260505-0
file: data/en.wikipedia.org/wiki/BQP-0.md
category: reference
title: BQP
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/BQP
date_saved: 2026-05-05T11:06:41.292100+00:00
instance: kb-cron
parent: bqp-20260505-0
summary:
In computational complexity theory, bounded-error quantum polynomial time (BQP) is the class of decision problems solvable by a quantum computer in polynomial time, with an error probability of at most 1/3 for all instances. It is the quantum analogue to the complexity class BPP. A decision problem is a member of BQP if there exists a quantum algorithm (an algorithm that runs on a quantum computer) that solves the decision problem with high probability and is guaranteed to run in polynomial time. A run of the algorithm will correctly solve the decision problem with a probability of at least 2/3. == Definition == BQP can be viewed as the languages associated with certain bounded-error uniform families of quantum circuits. A language L is in BQP if and only if there exists a polynomial-time uniform family of quantum circuits { Q n : n ∈ N } {\displaystyle \{Q_{n}\colon n\in \mathbb {N} \}} , such that For all n ∈ N {\displaystyle n\in \mathbb {N} } , Qn takes n qubits as input and outputs 1 bit For all x in L, P r ( Q | x | ( x ) = 1 ) ≥ 2 3 {\displaystyle \mathrm {Pr}


id: bqp-20260505-1
file: data/en.wikipedia.org/wiki/BQP-1.md
category: reference
title: BQP
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/BQP
date_saved: 2026-05-05T11:06:41.292100+00:00
instance: kb-cron
parent: bqp-20260505-0
summary:
==== APPROX-QCIRCUIT-PROB ==== The APPROX-QCIRCUIT-PROB problem is complete for efficient quantum computation, and the version presented below is complete for the Promise-BQP complexity class (and not for the total BQP complexity class, for which no complete problems are known). APPROX-QCIRCUIT-PROB's completeness makes it useful for proofs showing the relationships between other complexity classes and BQP. Given a description of a quantum circuit C acting on n qubits with m gates, where m is a polynomial in n and each gate acts on one or two qubits, and two numbers α , β ∈ [ 0 , 1 ] , α > β {\displaystyle \alpha ,\beta \in [0,1],\alpha >\beta } , distinguish between the following two cases: measuring the first qubit of the state C | 0 ⟩ ⊗ n {\displaystyle C|0\rangle ^{\otimes n}} yields | 1 ⟩ {\displaystyle |1\rangle } with probability ≥ α {\displaystyle \geq \alpha } measuring the first qubit of the state C | 0 ⟩ ⊗ n {\displaystyle C|0\rangle ^{\otimes n}} yields | 1 ⟩ {\displaystyle |1\rangle } with probability ≤ β {\displaystyle \leq \beta } Here, there is a promise on the inputs as the problem does not specify the behavior if an instance is


id: bqp-20260505-2
file: data/en.wikipedia.org/wiki/BQP-2.md
category: reference
title: BQP
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/BQP
date_saved: 2026-05-05T11:06:41.292100+00:00
instance: kb-cron
parent: bqp-20260505-0
summary:
Consider a quantum circuit C, which consists of t gates, g 1 , g 2 , ⋯ , g m {\displaystyle g_{1},g_{2},\cdots ,g_{m}} , where each g j {\displaystyle g_{j}} comes from a universal gate set and acts on at most two qubits. To understand what the sum of histories is, we visualize the evolution of a quantum state given a quantum circuit as a tree. The root is the input | 0 ⟩ ⊗ n {\displaystyle |0\rangle ^{\otimes n}} , and each node in the tree has 2 n {\displaystyle 2^{n}} children, each representing a state in C n {\displaystyle \mathbb {C} ^{n}} . The weight on a tree edge from a node in j-th level representing a state | x ⟩ {\displaystyle |x\rangle } to a node in j + 1 {\displaystyle j+1} -th level representing a state | y ⟩ {\displaystyle |y\rangle } is ⟨ y | g j + 1 | x ⟩ {\displaystyle \langle y|g_{j+1}|x\rangle } , the amplitude of | y ⟩ {\displaystyle |y\rangle } after applying g j + 1 {\displaystyle g_{j+1}} on | x ⟩ {\displaystyle |x\rangle } . The transition amplitude of a root-to-leaf path is the product of all the


id: cat-qubit-quantum-computer-20260505-0
file: data/en.wikipedia.org/wiki/Cat_qubit_quantum_computer-0.md
category: reference
title: Cat qubit quantum computer
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cat_qubit_quantum_computer
date_saved: 2026-05-05T11:06:42.433230+00:00
instance: kb-cron
parent: cat-qubit-quantum-computer-20260505-0
summary:
A cat qubit quantum computer is one proposed approach to a large-scale quantum computer based on Schrödinger cat states. Cat states are superpositions of two coherent states of light. Cat qubits encode quantum information in these states. They are designed to provide built in protection against certain types of errors, particularly bit flips, making quantum error correction more efficient in superconducting circuits. The approach is being developed by Alice & Bob and Amazon Web Services (AWS), among others. == Background == Cat qubits use coherent states of a quantum harmonic oscillator—microwave photons trapped in a superconducting resonator—as their logical 0 and 1 states. The name derives from the Schrödinger's cat thought experiment, in which a system exists in a superposition of two macroscopically distinct states. Errors in quantum computation generally occur as bit-flip errors — changing a qubit's logical state from 0 to 1 or vice versa — and phase-flip errors, which alter the relative phase between superposed states. The key property of cat qubits is that the probability of a bit-flip decreases exponentially with the number of photons in the coherent state. In conventional superconducting transmon-based architectures using surface codes, correcting both types of errors can require a significant


id: chemical-computer-20260505-0
file: data/en.wikipedia.org/wiki/Chemical_computer-0.md
category: reference
title: Chemical computer
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Chemical_computer
date_saved: 2026-05-05T11:06:43.894478+00:00
instance: kb-cron
parent: chemical-computer-20260505-0
summary:
A chemical computer, also called a reaction-diffusion computer, Belousov–Zhabotinsky (BZ) computer, or gooware computer, is an unconventional computer based on a semi-solid chemical "soup" where data are represented by varying concentrations of chemicals. The computations are performed by naturally occurring chemical reactions. == Background == Originally chemical reactions were seen as a simple move towards a stable equilibrium which was not very promising for computation. This was changed by a discovery made by Boris Belousov, a Soviet scientist, in the 1950s. He created a chemical reaction between different salts and acids that swing back and forth between being yellow and clear because the concentration of the different components changes up and down in a cyclic way. At the time this was considered impossible because it seemed to go against the second law of thermodynamics, which says that in a closed system the entropy will only increase over time, causing the components in the mixture to distribute themselves until equilibrium is gained and making any changes in the concentration impossible. But modern theoretical analyses shows sufficiently complicated reactions can indeed comprise wave phenomena without breaking the laws of nature. (A convincing directly visible demonstration was achieved by Anatol Zhabotinsky with the


id: cirac-zoller-controlled-not-gate-20260505-0
file: data/en.wikipedia.org/wiki/Cirac–Zoller_controlled-NOT_gate-0.md
category: reference
title: Cirac–Zoller controlled-NOT gate
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cirac–Zoller_controlled-NOT_gate
date_saved: 2026-05-05T11:06:45.070213+00:00
instance: kb-cron
parent: cirac-zoller-controlled-not-gate-20260505-0
summary:
The Cirac–Zoller controlled-NOT gate is an implementation of the controlled-NOT (CNOT) quantum logic gate using cold trapped ions that was proposed by Ignacio Cirac and Peter Zoller in 1995 and represents the central ingredient of the Cirac–Zoller proposal for a trapped-ion quantum computer. The key idea of the Cirac–Zoller proposal is to mediate the interaction between the two qubits through the joint motion of the complete chain of trapped ions. The quantum CNOT gate acts on two qubits and can entangle them. It forms part of the standard universal set of gates, meaning that any gate (unitary transformation) on the N {\displaystyle N} -qubit Hilbert space can be approximated to arbitrary precision by a sequence of gates from the universal set. The Cirac–Zoller gate was experimentally first realized in 2003 (in slightly modified form) at the University of Innsbruck, Austria by Ferdinand Schmidt-Kaler and coworkers in the group of Rainer Blatt using two calcium ions. == Procedure == The qubits on which the Cirac–Zoller gate operates are represented by two internal states, ground state and excited state (called in the following g and e) of trapped ions. An additional auxiliary excited state a is used to implement the gate. Due


id: circuit-layer-operations-per-second-20260505-0
file: data/en.wikipedia.org/wiki/Circuit_Layer_Operations_per_Second-0.md
category: reference
title: Circuit Layer Operations per Second
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Circuit_Layer_Operations_per_Second
date_saved: 2026-05-05T11:06:46.190126+00:00
instance: kb-cron
parent: circuit-layer-operations-per-second-20260505-0
summary:
Circuit Layer Operations per Second (CLOPS) is a benchmarking metric of quantum computers developed by IBM in 2021. While Quantum volume is more indicative of a qubit's performance and quality, CLOPS is a measure of a quantum computer’s execution speed. CLOPS incorporates both the time to run a circuit as well as the real-time and near-time classical computation, enabling it to serve as a holistic single measure of speed. CLOPS in conjunction with the number of qubits and the quantum volume was originally envisioned by IBM to be the 3 core metrics for comparing quantum devices. == Redefinition == Originally CLOPS was designed to be related to quantum volume, in the sense that each circuit layer was idealized square quantum volume circuits. However, in 2023 IBM created a new definition of CLOPS which is related to a specific hardware layer. The different versions are differentiated with a subscript: CLOPSv for virtual and CLOPSh for hardware. Functionally, the core difference is that instead of using quantum volume in the calculation, a different metric known as layer fidelity is used instead, measured by the error per layered gate (ELPG) protocol. This enables different hardware with different quantum volumes to be more accurately


id: classical-shadow-20260505-0
file: data/en.wikipedia.org/wiki/Classical_shadow-0.md
category: reference
title: Classical shadow
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Classical_shadow
date_saved: 2026-05-05T11:06:47.340833+00:00
instance: kb-cron
parent: classical-shadow-20260505-0
summary:
In quantum computing, classical shadow is a protocol for predicting expectation values of a quantum state using only a logarithmic number of measurements. Given an unknown state ρ {\displaystyle \rho } , a tomographically complete set of gates U {\displaystyle U} (e.g. Clifford gates), a set of M {\displaystyle M} observables { O i } {\displaystyle \{O_{i}\}} and a quantum channel E {\displaystyle {\mathcal {E}}} defined by randomly sampling from U {\displaystyle U} , applying it to ρ {\displaystyle \rho } and measuring the resulting state, predict the expectation values tr ⁡ ( O i ρ ) {\displaystyle \operatorname {tr} (O_{i}\rho )} . A list of classical shadows S {\displaystyle S} is created using ρ {\displaystyle \rho } , U {\displaystyle U} and E {\displaystyle {\mathcal {E}}} by running a Shadow generation algorithm. When predicting the properties of ρ {\displaystyle \rho } , a Median-of-means estimation algorithm is used to deal with the outliers in S {\displaystyle S} . Classical shadow is useful for direct fidelity estimation, entanglement verification, estimating correlation functions, and predicting entanglement entropy. Recently, researchers have built on classical shadow to devise provably efficient classical machine learning algorithms for a wide range of quantum many-body problems. For


id: cloud-based-quantum-computing-20260505-0
file: data/en.wikipedia.org/wiki/Cloud-based_quantum_computing-0.md
category: reference
title: Cloud-based quantum computing
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cloud-based_quantum_computing
date_saved: 2026-05-05T11:06:48.511879+00:00
instance: kb-cron
parent: cloud-based-quantum-computing-20260505-0
summary:
Cloud-based quantum computing refers to the remote access of quantum computing resources—such as quantum emulators, simulators, or processors—via the internet. Cloud access enables users to develop, test, and execute quantum algorithms without the need for direct interaction with specialized hardware, facilitating broader participation in quantum software development and experimentation. In 2016, IBM launched the IBM Quantum Experience, one of the first publicly accessible quantum processors connected to the cloud. In early 2017, researchers at Rigetti Computing demonstrated programmable quantum cloud access through their software platform Forest, which included the pyQuil Python library. Since the early-2020s, cloud-based quantum computing has grown significantly, with multiple providers offering access to a variety of quantum hardware modalities, including superconducting qubits, trapped ions, neutral atoms, and photonic systems. Major platforms such as Amazon Braket, Azure Quantum, and qBraid aggregate quantum devices from hardware developers like IonQ, Rigetti Computing, QuEra, Pasqal, Oxford Quantum Circuits, and IBM Quantum. These platforms provide unified interfaces for users to write and execute quantum algorithms across diverse backends, often supporting open-source SDKs such as Qiskit, Cirq, and PennyLane. The proliferation of cloud-based access has played a key role in accelerating quantum education, algorithm research, and early-stage application development by lowering the


id: list-of-companies-involved-in-quantum-computing-communication-or-sensing-20260505-0
category: reference
title: List of companies involved in quantum computing, communication or sensing
tags: science, encyclopedia
date_saved: 2026-05-05T11:06:49.720687+00:00
instance: kb-cron
parent: list-of-companies-involved-in-quantum-computing-communication-or-sensing-20260505-0
file:
data/en.wikipedia.org/wiki/List_of_companies_involved_in_quantum_computing,_communication_or_sensing-0.md

summary:
This article lists the companies worldwide engaged in the development of quantum computing, quantum communication and quantum sensing. Quantum computing and communication are two sub-fields of quantum information science, which describes and theorizes information science in terms of quantum physics. While the fundamental unit of classical information is the bit, the basic unit of quantum information is the qubit. Quantum sensing is the third main sub-field of quantum technologies and it focus consists in taking advantage of the quantum states sensitivity to the surrounding environment to perform atomic scale measurements. == Company details == == See also == Quantum programming Quantum supremacy List of quantum processors == References == == Further reading == Quantum Computing Report's list of quantum players The Quantum Insider's list of quantum computing companies

source_url:
https://en.wikipedia.org/wiki/List_of_companies_involved_in_quantum_computing,_communication_or_sensing


id: cross-entropy-benchmarking-20260505-0
file: data/en.wikipedia.org/wiki/Cross-entropy_benchmarking-0.md
category: reference
title: Cross-entropy benchmarking
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cross-entropy_benchmarking
date_saved: 2026-05-05T11:06:50.850403+00:00
instance: kb-cron
parent: cross-entropy-benchmarking-20260505-0
summary:
Cross-entropy benchmarking (XEB) is a statistical measure used to evaluate the performance in random circuit sampling experiments. It quantifies how strongly experimental samples correlate with the ideal output distribution and has been used in demonstrations of quantum supremacy. == Definition == Let C {\displaystyle C} be an n {\displaystyle n} -qubit quantum circuit. The output probability for bitstrings x ∈ { 0 , 1 } n {\displaystyle x\in \{0,1\}^{n}} for C {\displaystyle C} acting on all 0 input 0 n {\displaystyle 0^{n}} is P ( x ) = | ⟨ x | C | 0 n ⟩ | 2 {\displaystyle P(x)=|\langle x|C|0^{n}\rangle |^{2}} . Given k {\displaystyle k} samples { x i } i = 1 k {\displaystyle \{x_{i}\}_{i=1}^{k}} obtained from an experimental device, the (linear) cross-entropy benchmarking fidelity is defined as F X E B = 2 n ⟨ P ( x i ) ⟩ k − 1 = 2 n k ( ∑ i = 1 k | ⟨ 0 n | C | x i ⟩ | 2 ) − 1 {\displaystyle F_{\rm {XEB}}=2^{n}\langle P(x_{i})\rangle _{k}-1={\frac {2^{n}}{k}}\left(\sum _{i=1}^{k}|\langle 0^{n}|C|x_{i}\rangle |^{2}\right)-1} == Interpretation == If F X E B = 1 {\displaystyle F_{XEB}=1} , the samples were collected


id: d-wave-systems-20260505-0
file: data/en.wikipedia.org/wiki/D-Wave_Systems-0.md
category: reference
title: D-Wave Systems
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/D-Wave_Systems
date_saved: 2026-05-05T11:06:52.071639+00:00
instance: kb-cron
parent: d-wave-systems-20260505-0
summary:
D-Wave Quantum Inc. is a quantum computing company with locations in Palo Alto, California and Burnaby, British Columbia. D-Wave claims to be the world's first company to sell computers that exploit quantum effects in their operation. D-Wave's early customers include Lockheed Martin, the University of Southern California, Google/NASA, and Los Alamos National Laboratory. D-Wave does not implement a generic, universal quantum computer; instead, their computers implement specialized quantum annealing. == History == D-Wave was founded by Haig Farris, Geordie Rose, Bob Wiens, and Alexandre Zagoskin in 1999. Farris taught a business course at the University of British Columbia (UBC), where Rose obtained his PhD, and Zagoskin was a postdoctoral fellow. The company name refers to their first qubit designs, which used d-wave superconductors. D-Wave operated from various locations in Vancouver, British Columbia, and laboratory spaces at UBC before moving to its current location in the neighboring suburb of Burnaby. D-Wave also has offices in Palo Alto, California and Vienna, California, USA. D-Wave operated as an offshoot from UBC, while maintaining ties with the Department of Physics and Astronomy. It funded academic research in quantum computing, thus building a collaborative network of research scientists. The company collaborated with several universities and


id: d-wave-systems-20260505-1
file: data/en.wikipedia.org/wiki/D-Wave_Systems-1.md
category: reference
title: D-Wave Systems
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/D-Wave_Systems
date_saved: 2026-05-05T11:06:52.071639+00:00
instance: kb-cron
parent: d-wave-systems-20260505-0
summary:
=== Orion prototype === On February 13, 2007, D-Wave demonstrated the Orion system, running three different applications at the Computer History Museum in Mountain View, California. This marked the first public demonstration of, supposedly, a quantum computer and associated service. The first application, an example of pattern matching, performed a search for a similar compound to a known drug within a database of molecules. The next application computed a seating arrangement for an event subject to compatibilities and incompatibilities between guests. The last involved solving a Sudoku puzzle. The processors at the heart of D-Wave's "Orion quantum computing system" are designed for use as hardware accelerator processors rather than general-purpose computer microprocessors. The system is designed to solve a particular NP-complete problem related to the two-dimensional Ising model in a magnetic field. D-Wave terms the device as a 16-qubit superconducting adiabatic quantum computer processor. According to the company, a conventional front-end running an application that requires the solution of an NP-complete problem, such as pattern matching, passes the problem to the Orion system. According to Geordie Rose, founder and Chief Technology Officer of D-Wave, NP-complete problems "are probably not exactly solvable, no matter how big, fast or advanced computers get";


id: d-wave-systems-20260505-2
file: data/en.wikipedia.org/wiki/D-Wave_Systems-2.md
category: reference
title: D-Wave Systems
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/D-Wave_Systems
date_saved: 2026-05-05T11:06:52.071639+00:00
instance: kb-cron
parent: d-wave-systems-20260505-0
summary:
== Incidents and criticisms == Despite its pioneering role in quantum annealing, D-Wave has faced criticism regarding the practical utility and commercial viability of its systems. In March 2025, D-Wave announced that it had achieved what it described as "quantum supremacy," reporting that its latest quantum annealer solved a specialized optimization problem faster than the world's most powerful classical supercomputers could replicate the result. The Wall Street Journal noted that while the experiment demonstrated a performance gap favoring D-Wave's hardware, skeptics argued the problem was carefully chosen to highlight the system's strengths and did not reflect general-purpose computational tasks. Critics further observed that advances in classical algorithms might soon close this benchmark gap, suggesting that D-Wave's claimed supremacy may be limited to narrow, contrived applications rather than broad, real-world problems. In April 2025, independent investment research firm Kerrisdale Capital argued that D-Wave's market valuation was "disconnected from its stagnating revenue and lack of broad commercial adoption," highlighting concerns over significant share dilution and questioning the company's path to profitability. == See also == List of companies involved in quantum computing or communication Adiabatic quantum computation Analog computer AQUA@home Flux qubit Quantum annealing Superconducting quantum computing IBM Q System One ==


id: david-deutsch-20260505-0
file: data/en.wikipedia.org/wiki/David_Deutsch-0.md
category: reference
title: David Deutsch
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/David_Deutsch
date_saved: 2026-05-05T11:06:53.298460+00:00
instance: kb-cron
parent: david-deutsch-20260505-0
summary:
David Elieser Deutsch ( DOYTCH; born 18 May 1953) is a British physicist at the University of Oxford who is often described as the "father of quantum computing". He is a visiting professor in the Department of Atomic and Laser Physics at the Centre for Quantum Computation (CQC) in the Clarendon Laboratory of the University of Oxford. He pioneered the field of quantum computation by formulating a description for a quantum Turing machine, as well as specifying an algorithm designed to run on a quantum computer. He is a proponent of the many-worlds interpretation of quantum mechanics. == Education == Deutsch was born to a Jewish family in Haifa, Israel, on 18 May 1953, the son of Oskar and Tikva Deutsch. David attended Geneva House school in Cricklewood, London. His parents owned and ran the Alma restaurant on Cricklewood Broadway. He later attended William Ellis School in Highgate before reading Natural Sciences at Clare College, Cambridge, and taking Part III of the Mathematical Tripos. He went on to Wolfson College, Oxford for his doctorate in theoretical physics on quantum field theory in curved space-time, supervised by Dennis Sciama and Philip Candelas. == Career and research == His work on quantum


id: david-deutsch-20260505-1
file: data/en.wikipedia.org/wiki/David_Deutsch-1.md
category: reference
title: David Deutsch
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/David_Deutsch
date_saved: 2026-05-05T11:06:53.298460+00:00
instance: kb-cron
parent: david-deutsch-20260505-0
summary:
== Personal life == Deutsch is a founding member of the parenting and educational method Taking Children Seriously. === Views on Antisemitism and Zionism === Deutsch describes antisemitism as a recurring pattern of irrational thinking, present in many cultures, whose function is to justify harming Jews simply for being Jews. He argues that "the pattern" persists because, when old justifications for hating Jews lose relevance, new ones are invented to take their place. Deutsch compares this phenomenon to the way gold retains its high value, not because of any inherent quality, but because people know that other people value it. He regards Zionism as the contemporary Jewish response to this pattern and identifies himself as an atheist Zionist. === Views on Brexit === Deutsch supported Brexit, with his advocacy quoted by then-government adviser, Dominic Cummings, and reported by The New Yorker in January 2020. Michael Gove mentioned Deutsch's viewpoint during a BBC Brexit debate. Regarding the debate, Deutsch later commented: In Britain there is a clear path if you have a grievance, you can join a pressure-group, the pressure-group will pressure the government, or you can see your MP, and the MP will see the grievance building up, and so-on.


id: andrew-dzurak-20260505-0
file: data/en.wikipedia.org/wiki/Andrew_Dzurak-0.md
category: reference
title: Andrew Dzurak
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Andrew_Dzurak
date_saved: 2026-05-05T11:06:54.451250+00:00
instance: kb-cron
parent: andrew-dzurak-20260505-0
summary:
Andrew Dzurak is an Australian physicist and engineer, known for his work in quantum computing. He is the CEO and founder of Diraq, a start-up that is developing a scalable quantum computer based on single electron spins in silicon. He is a Scientia Professor in Quantum Engineering at the University of New South Wales (UNSW), an ARC Laureate Fellow and a member of the executive board of the Sydney Quantum Academy. == Education == Dzurak completed his Bachelor of Science at the University of Sydney in 1987. He then earned his PhD in experimental physics from the University of Cambridge in 1993, under the supervision of Professor Sir Michael Pepper, FRS. == Research == While in Cambridge, Dzurak studied hot electron and ballistic transport in various semiconductor nanostructures, including quantum point contact and quantum dot systems, which were then newly discovered. He also became an expert in the fabrication and low-temperature measurement of nanoelectronic devices, skills that he applied upon his return to Australia. In 1994, Dzurak took up a Vice-Chancellor's Research Fellowship in the School of Physics at the UNSW, followed by an ARC Postdoctoral Research Fellowship in 1996. He was the founding Director (2007–2022) of ANFF–NSW, the NSW


