# kb

id: binding-problem-20260505-2
file: data/en.wikipedia.org/wiki/Binding_problem-2.md
category: reference
title: Binding problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Binding_problem
date_saved: 2026-05-05T11:04:16.760782+00:00
instance: kb-cron
parent: binding-problem-20260505-0
summary:
=== Summary of problem === Smythies defines the combination problem, also known as the subjective unity of perception, as "How do the brain mechanisms actually construct the phenomenal object?". Revonsuo equates this to "consciousness-related binding", emphasizing the entailment of a phenomenal aspect. As Revonsuo explores in 2006, there are nuances of difference beyond the basic BP1:BP2 division. Smythies speaks of constructing a phenomenal object ("local unity" for Revonsuo) but philosophers such as René Descartes, Gottfried Wilhelm Leibniz, Immanuel Kant, and James (see Brook and Raymont) have typically been concerned with the broader unity of a phenomenal experience ("global unity" for Revonsuo) – which, as Bayne illustrates may involve features as diverse as seeing a book, hearing a tune and feeling an emotion. Further discussion will focus on this more general problem of how sensory data that may have been segregated into, for instance, "blue square" and "yellow circle" are to be re-combined into a single phenomenal experience of a blue square next to a yellow circle, plus all other features of their context. There is a wide range of views on just how real this "unity" is, but the existence of medical conditions in which it appears to be subjectively


id: binding-problem-20260505-3
file: data/en.wikipedia.org/wiki/Binding_problem-3.md
category: reference
title: Binding problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Binding_problem
date_saved: 2026-05-05T11:04:16.760782+00:00
instance: kb-cron
parent: binding-problem-20260505-0
summary:
==== fMRI work ==== Stoll and colleagues conducted an fMRI experiment to see whether participants would view a dynamic bistable stimulus globally or locally. Responses in lower visual cortical regions were suppressed when participants viewed the stimulus globally. However, if global perception was without shape grouping, higher cortical regions were suppressed. This experiment shows that higher order cortex is important in perceptual grouping. Grassi and colleagues used three different motion stimuli to investigate scene segmentation or how meaningful entities are grouped together and separated from other entities in a scene. Across all stimuli, scene segmentation was associated with increased activity in the posterior parietal cortex and decreased activity in lower visual areas. This suggests that the posterior parietal cortex is important for viewing an integrated whole. ==== EEG work ==== Mersad and colleagues used an EEG frequency tagging technique to differentiate between brain activity for the integrated whole object and brain activity for parts of the object. The results showed that the visual system binds two humans in close proximity as part of an integrated whole. These results are consistent with evolutionary theories that face-to-face bodies are one of the earliest representations of social interaction. It also supports other experimental


id: binding-problem-20260505-4
file: data/en.wikipedia.org/wiki/Binding_problem-4.md
category: reference
title: Binding problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Binding_problem
date_saved: 2026-05-05T11:04:16.760782+00:00
instance: kb-cron
parent: binding-problem-20260505-0
summary:
=== Modern theories === Daniel Dennett has proposed that we, as humans, sensing our experiences as individual single events is illusory and that, instead, at any one time there are "multiple drafts" of sensory patterns at multiple sites. Each would only cover a fragment of what we think we experience. Arguably, Dennett is claiming that consciousness is not unified and there is no phenomenal binding problem. Most philosophers have difficulty with this position (see Bayne), but some physiologists agree with it. In particular, the demonstration of perceptual asynchrony in psychophysical experiments by Moutoussis and Zeki, where color is perceived before orientation of lines and before motion by 40 and 80 ms respectively, constitutes an argument that, over these very short time periods, different attributes are consciously perceived at different times, leading to the view that at least over these brief periods of time after visual stimulation, different events are not bound to each other, leading to the view of a disunity of consciousness, at least over these brief time intervals. Dennett's view might be in keeping with evidence from recall experiments and change blindness purporting to show that our experiences are much less rich than we sense them to be


id: binding-problem-20260505-5
file: data/en.wikipedia.org/wiki/Binding_problem-5.md
category: reference
title: Binding problem
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Binding_problem
date_saved: 2026-05-05T11:04:16.760782+00:00
instance: kb-cron
parent: binding-problem-20260505-0
summary:
== Shared intentionality and binding == According to bioengineer Igor Val Danilov, the mother–fetus neurocognitive model—knowledge about neurophysiological processes during shared intentionality—can reveal insights into the binding problem and even the perception of object development since intentionality succeeds before organisms confront the binding problem. Indeed, at the beginning of life, the environment is the cacophony of stimuli: electromagnetic waves, chemical interactions, and pressure fluctuations. Because the environment is uncategorised for the organisms at this beginning stage of development, the sensation is too limited by the noise to solve the cue problem—the relevant stimulus cannot overcome the noise magnitude if it passes through the senses. While very young organisms need to combine objects, background and abstract or emotional features into a single experience for building the representation of the surrounded reality, they cannot distinguish relevant sensory stimuli independently to integrate them into object representations. Even the embodied dynamical system approach cannot get around the cue to noise problem. The application of embodied information requires an already categorised environment onto objects—holistic representation of reality—which occurs through (and only after the emergence of) perception and intentionality. In short, properties of the mother's heart—the electromagnetic and acoustic oscillations—converge the neuronal activity of both nervous


id: biochemistry-of-alzheimer-s-disease-20260505-0
file: data/en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease-0.md
category: reference
title: Biochemistry of Alzheimer's disease
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease
date_saved: 2026-05-05T11:04:17.929946+00:00
instance: kb-cron
parent: biochemistry-of-alzheimer-s-disease-20260505-0
summary:
The biochemistry of Alzheimer's disease, the most common cause of dementia, is not yet very well understood. Alzheimer's disease (AD) has been identified as a proteopathy: a protein misfolding disease due to the accumulation of abnormally folded amyloid beta (Aβ) protein in the brain. Amyloid beta is a short peptide that is an abnormal proteolytic byproduct of the transmembrane protein amyloid-beta precursor protein (APP), whose function is unclear but thought to be involved in neuronal development. The presenilins are components of proteolytic complex involved in APP processing and degradation. Amyloid beta monomers are soluble and contain short regions of beta sheet and polyproline II helix secondary structures in solution, though they are largely alpha helical in membranes; however, at sufficiently high concentration, they undergo a dramatic conformational change to form a beta sheet-rich tertiary structure that aggregates to form amyloid fibrils. These fibrils and oligomeric forms of Aβ deposit outside neurons in formations known as senile plaques. There are different types of plaques, including the diffuse, compact, cored or neuritic plaque types, as well as Aβ deposits in the walls of small blood vessel walls in the brain called cerebral amyloid angiopathy. AD is also considered a tauopathy due to


id: biochemistry-of-alzheimer-s-disease-20260505-1
file: data/en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease-1.md
category: reference
title: Biochemistry of Alzheimer's disease
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease
date_saved: 2026-05-05T11:04:17.929946+00:00
instance: kb-cron
parent: biochemistry-of-alzheimer-s-disease-20260505-0
summary:
== Disease mechanisms == While the gross histological features of AD in the brain have been well characterized, several different hypotheses have been advanced regarding the primary cause. Among the oldest hypotheses is the cholinergic hypothesis, which suggests that deficiency in cholinergic signaling initiates the progression of the disease. Current theories establish that both misfolding tau protein inside the cell and aggregation of amyloid beta outside the cell initiates the cascade leading to AD pathology. Newer potential hypotheses propose metabolic factors, vascular disturbance, lipid invasion and chronically elevated inflammation in the brain as contributing factors to AD. The amyloid beta hypothesis of molecular initiation have become dominant among many researchers to date. The amyloid and tau hypothesis are the most widely accepted. === Tau hypothesis === The hypothesis that tau is the primary causative factor has long been grounded in the observation that deposition of amyloid plaques does not correlate well with neuron loss. A mechanism for neurotoxicity has been proposed based on the loss of microtubule-stabilizing tau protein that leads to the degradation of the cytoskeleton. However, consensus has not been reached on whether tau hyperphosphorylation precedes or is caused by the formation of the abnormal helical filament aggregates.


id: biochemistry-of-alzheimer-s-disease-20260505-2
file: data/en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease-2.md
category: reference
title: Biochemistry of Alzheimer's disease
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease
date_saved: 2026-05-05T11:04:17.929946+00:00
instance: kb-cron
parent: biochemistry-of-alzheimer-s-disease-20260505-0
summary:
=== Historical cholinergic hypothesis === The cholinergic hypothesis of AD development was first proposed in 1976 by Peter Davies and A.J.F Maloney. It claimed that Alzheimer's begins as a deficiency in the production of acetylcholine, a vital neurotransmitter. Much early therapeutic research was based on this hypothesis, including restoration of the "cholinergic nuclei". The possibility of cell-replacement therapy was investigated on the basis of this hypothesis. All of the first-generation anti-Alzheimer's medications are based on this hypothesis and work to preserve acetylcholine by inhibiting acetylcholinesterases (enzymes that break down acetylcholine). These medications, though sometimes beneficial, have not led to a cure. In all cases, they have served to only treat symptoms of the disease and have neither halted nor reversed it. These results and other research have led to the conclusion that acetylcholine deficiencies may not be directly causal, but are a result of widespread brain tissue damage, damage so widespread that cell-replacement therapies are likely to be impractical. More recent findings center on the effects of the misfolded and aggregated proteins, amyloid beta and tau: tau protein abnormalities may initiate the disease cascade, then beta amyloid deposits progress the disease. === Glucose consumption === The human brain is one


id: biochemistry-of-alzheimer-s-disease-20260505-3
file: data/en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease-3.md
category: reference
title: Biochemistry of Alzheimer's disease
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease
date_saved: 2026-05-05T11:04:17.929946+00:00
instance: kb-cron
parent: biochemistry-of-alzheimer-s-disease-20260505-0
summary:
=== Oxidative stress === Oxidative stress is emerging as a key factor in the pathogenesis of AD. Reactive oxygen species (ROS) over-production is thought to play a critical role in the accumulation and deposition of amyloid beta in AD. Brains of AD patients have elevated levels of oxidative DNA damage in both nuclear and mitochondrial DNA, but the mitochondrial DNA has approximately 10-fold higher levels than nuclear DNA. Aged mitochondria may be the critical factor in the origin of neurodegeneration in AD. Even individuals with mild cognitive impairment, the phase between normal aging and early dementia, have increased oxidative damage in their nuclear and mitochondrial brain DNA (see Aging brain). Naturally occurring DNA double-strand breaks (DSBs) arise in human cells largely from single-strand breaks induced by various processes including the activity of reactive oxygen species, topoisomerases, and hydrolysis due to thermal fluctuations. In neurons DSBs are induced by a type II topoisomerase as part of the physiologic process of memory formation. DSBs are present in both neurons and astrocytes in the postmortem human hippocampus of AD patients at a higher level than in non-AD individuals. AD is associated with an accumulation of DSBs in neurons and astrocytes in the hippocampus


id: biochemistry-of-alzheimer-s-disease-20260505-4
file: data/en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease-4.md
category: reference
title: Biochemistry of Alzheimer's disease
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Biochemistry_of_Alzheimer's_disease
date_saved: 2026-05-05T11:04:17.929946+00:00
instance: kb-cron
parent: biochemistry-of-alzheimer-s-disease-20260505-0
summary:
=== Reelin hypothesis === A 1994 study showed that the isoprenoid changes in Alzheimer's disease differ from those occurring during normal aging and that this disease cannot, therefore, be regarded as a result of premature aging. During aging the human brain shows a progressive increase in levels of dolichol, a reduction in levels of ubiquinone, but relatively unchanged concentrations of cholesterol and dolichyl phosphate. In Alzheimer's disease, the situation is reversed with decreased levels of dolichol and increased levels of ubiquinone. The concentrations of dolichyl phosphate are also increased, while cholesterol remains unchanged. The increase in the sugar carrier dolichyl phosphate may reflect an increased rate of glycosylation in the diseased brain and the increase in the endogenous anti-oxidant ubiquinone an attempt to protect the brain from oxidative stress, for instance induced by lipid peroxidation. Ropren, identified previously in Russia, is neuroprotective in a rat model of Alzheimer's disease. A relatively recent hypothesis based mainly on rodent experiments links the onset of Alzheimer's disease to the hypofunction of the large extracellular protein reelin. A decrease of reelin in the human entorhinal cortex where the disease typically initiates is evident while compensatory increase of reelin levels in other brain structures of


id: catecholaldehyde-hypothesis-20260505-0
file: data/en.wikipedia.org/wiki/Catecholaldehyde_hypothesis-0.md
category: reference
title: Catecholaldehyde hypothesis
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Catecholaldehyde_hypothesis
date_saved: 2026-05-05T11:04:19.139868+00:00
instance: kb-cron
parent: catecholaldehyde-hypothesis-20260505-0
summary:
The catecholaldehyde hypothesis is a scientific theory positing that neurotoxic aldehyde metabolites of the catecholamine neurotransmitters dopamine and norepinephrine are responsible for neurodegenerative diseases involving loss of catecholaminergic neurons, for instance Parkinson's disease. The specific metabolites thought to be involved include 3,4-dihydroxyphenylacetaldehyde (DOPAL) and 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), which are formed from dopamine and norepinephrine by monoamine oxidase, respectively. These metabolites are subsequently inactivated and detoxified by aldehyde dehydrogenase (ALDH). DOPAL and DOPEGAL are monoaminergic neurotoxins in preclinical models and inhibition of and polymorphisms in ALDH are associated with Parkinson's disease. The catecholaldehyde hypothesis additionally posits that DOPAL oligomerizes with α-synuclein resulting in accumulation of oligomerized α-synuclein (i.e., synucleinopathy) and that this contributes to cytotoxicity. == See also == Amyloid hypothesis == References ==


id: cerebral-polyopia-20260505-0
file: data/en.wikipedia.org/wiki/Cerebral_polyopia-0.md
category: reference
title: Cerebral polyopia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cerebral_polyopia
date_saved: 2026-05-05T11:04:20.324237+00:00
instance: kb-cron
parent: cerebral-polyopia-20260505-0
summary:
Cerebral diplopia or polyopia describes seeing two or more images arranged in ordered rows, columns, or diagonals after fixation on a stimulus. The polyopic images occur monocular bilaterally (one eye open on both sides) and binocularly (both eyes open), differentiating it from ocular diplopia or polyopia. The number of duplicated images can range from one to hundreds. Some patients report difficulty in distinguishing the replicated images from the real images, while others report that the false images differ in size, intensity, or color. Cerebral polyopia is sometimes confused with palinopsia (visual trailing), in which multiple images appear while watching an object. However, in cerebral polyopia, the duplicated images are of a stationary object which are perceived even after the object is removed from the visual field. Movement of the original object causes all of the duplicated images to move, or the polyopic images disappear during motion. In palinoptic polyopia, movement causes each polyopic image to leave an image in its wake, creating hundreds of persistent images (entomopia). Infarctions, tumors, multiple sclerosis, trauma, encephalitis, migraines, and seizures have been reported to cause cerebral polyopia. Cerebral polyopia has been reported in extrastriate visual cortex lesions, which is important for detecting motion, orientation,


id: cerebral-polyopia-20260505-1
file: data/en.wikipedia.org/wiki/Cerebral_polyopia-1.md
category: reference
title: Cerebral polyopia
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cerebral_polyopia
date_saved: 2026-05-05T11:04:20.324237+00:00
instance: kb-cron
parent: cerebral-polyopia-20260505-0
summary:
== Theories of cerebral polyopia == The preliminary theory of cerebral polyopia proposed by Bender postulated that polyopia occurs as a result of instability of fixation due to occipital lobe disease. Under this explanation, small, involuntary eye movements that accompanied normal fixation were the cause of polyopic images. These involuntary eye movements lead to the development of new retinal and corresponding cortical regions that code for central vision called false maculae. Thus, polyopic images resulted from the stimulation of both the original and acquired maculae. However, Bender's theory does not account for recent studies in which fixation did not change and no eye movements were produced while polyopia was experienced, therefore polyopic images were not a result of involuntary eye movements. Instead, Cornblath offers a possible pathophysiological mechanism in which polyopia results from the recoding of visual receptive fields in primary visual cortex (Area V1). The report of polyopic images of complex objects at fixation suggests that the disorder is not limited to lower-order visual areas in occipital cortex (in which simple features such as borders and angles are encoded), but rather it involves the interaction between lower-order visual areas in the occipital lobe and higher-order visual areas in the


id: cortisol-awakening-response-20260505-0
file: data/en.wikipedia.org/wiki/Cortisol_awakening_response-0.md
category: reference
title: Cortisol awakening response
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Cortisol_awakening_response
date_saved: 2026-05-05T11:04:21.561040+00:00
instance: kb-cron
parent: cortisol-awakening-response-20260505-0
summary:
The cortisol awakening response (CAR) is an increase between 38% and 75% in cortisol levels peaking 30–45 minutes after awakening in the morning in some people. This rise is superimposed upon the late-night rise in cortisol which occurs before awakening. While its purpose is uncertain, it may be linked to the hippocampus' preparation of the hypothalamic-pituitary-adrenal axis (HPA) in order to face anticipated stress. Other research has challenged the idea that this elevation in morning cortisol is specifically linked to the onset of waking. == Description == Shortly after awakening, a sharp 38–75% (average 50%) increase occurs in the blood level of cortisol in about 77% of healthy people of all ages. The average level of salivary cortisol upon waking is roughly 15 nmol/L; 30 minutes later it may be 23 nmol/L, though there are wide variations. The cortisol awakening response reaches a maximum approximately 30 minutes after awakening though it may still be heightened by 34% an hour after waking. The pattern of this response to waking is relatively stable for any individual. Twin studies show its pattern is largely genetically determined since there is a heritability of 0.40 for the mean cortisol increase after awakening and 0.48 for


id: decision-making-20260505-0
file: data/en.wikipedia.org/wiki/Decision-making-0.md
category: reference
title: Decision-making
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Decision-making
date_saved: 2026-05-05T11:04:22.741043+00:00
instance: kb-cron
parent: decision-making-20260505-0
summary:
In psychology, decision-making (also spelled decision making and decisionmaking) is regarded as the cognitive process resulting in the selection of a belief or a course of action among several possible alternative options. It could be either rational or irrational. The decision-making process is a reasoning process based on assumptions of values, preferences and beliefs of the decision-maker. Every decision-making process produces a final choice, which may or may not prompt action. Research about decision-making is also published under the label problem solving, particularly in European psychological research. == Overview == Decision-making can be regarded as a problem-solving activity yielding a solution deemed to be optimal, or at least satisfactory. It is therefore a process which can be more or less rational or irrational and can be based on explicit or tacit knowledge and beliefs. Tacit knowledge is often used to fill the gaps in complex decision-making processes. Usually, both of these types of knowledge, tacit and explicit, are used together in the decision-making process. Human performance has been the subject of active research from several perspectives: Psychological: examining individual decisions in the context of a set of needs, preferences and values the individual has or seeks. Cognitive: the decision-making process


id: decision-making-20260505-1
file: data/en.wikipedia.org/wiki/Decision-making-1.md
category: reference
title: Decision-making
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Decision-making
date_saved: 2026-05-05T11:04:22.741043+00:00
instance: kb-cron
parent: decision-making-20260505-0
summary:
The first is analysis process paralysis. This type of paralysis is often spoken of as a cyclical process. One is unable to make a decision because they get stuck going over the information again and again for fear of making the wrong decision. The second is decision precision paralysis. This paralysis is cyclical, just like the first one, but instead of going over the same information, the decision-maker will find new questions and information from their analysis and that will lead them to explore into further possibilities rather than making a decision. The third is risk uncertainty paralysis. This paralysis occurs when the decision-maker wants to eliminate any uncertainty but the examination of provided information is unable to get rid of all uncertainty. === Extinction by instinct === On the opposite side of analysis paralysis is the phenomenon called extinction by instinct. Extinction by instinct is the state that a person is in when they make careless decisions without detailed planning or thorough systematic processes. Extinction by instinct can possibly be fixed by implementing a structural system, like checks and balances into a group or one's life. Analysis paralysis is the exact opposite where a group's schedule could be saturated


id: decision-making-20260505-2
file: data/en.wikipedia.org/wiki/Decision-making-2.md
category: reference
title: Decision-making
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Decision-making
date_saved: 2026-05-05T11:04:22.741043+00:00
instance: kb-cron
parent: decision-making-20260505-0
summary:
=== Group === Consensus decision-making tries to avoid "winners" and "losers". Consensus requires that a majority approve a given course of action, but that the minority agree to go along with the course of action. In other words, if the minority opposes the course of action, consensus requires that the course of action be modified to remove objectionable features. Voting-based methods: Majority requires support from more than 50% of the members of the group. Thus, the bar for action is lower than with consensus. See also Condorcet method. Plurality, where the largest faction in a group decides, even if it falls short of a majority. Score voting (or range voting) lets each member score one or more of the available options, specifying both preference and intensity of preference information. The option with the highest total or average is chosen. This method has experimentally been shown to produce the lowest Bayesian regret among common voting methods, even when voters are strategic. It addresses issues of voting paradox and majority rule. See also approval voting. Quadratic voting allows participants to cast their preference and intensity of preference for each decision (as opposed to a simple for or against decision). As in score


id: decision-making-20260505-3
file: data/en.wikipedia.org/wiki/Decision-making-3.md
category: reference
title: Decision-making
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Decision-making
date_saved: 2026-05-05T11:04:22.741043+00:00
instance: kb-cron
parent: decision-making-20260505-0
summary:
Orientation. Members meet for the first time and start to get to know each other. Conflict. Once group members become familiar with each other, disputes, little fights and arguments occur. Group members eventually work it out. Emergence. The group begins to clear up vague opinions by talking about them. Reinforcement. Members finally make a decision and provide justification for it. It is said that establishing critical norms in a group improves the quality of decisions, while the majority of opinions (called consensus norms) do not. Conflicts in socialization are divided in to functional and dysfunctional types. Functional conflicts are mostly the questioning the managers assumptions in their decision making and dysfunctional conflicts are like personal attacks and every action which decrease team effectiveness. Functional conflicts are the better ones to gain higher quality decision-making caused by the increased team knowledge and shared understanding. == Rational and irrational == In economics, it is thought that if humans are rational and free to make their own decisions, then they would behave according to rational choice theory. Rational choice theory says that a person consistently makes choices that lead to the best situation for themselves, taking into account all available considerations including costs


id: decision-making-20260505-4
file: data/en.wikipedia.org/wiki/Decision-making-4.md
category: reference
title: Decision-making
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Decision-making
date_saved: 2026-05-05T11:04:22.741043+00:00
instance: kb-cron
parent: decision-making-20260505-0
summary:
=== Adults === Adults are generally better able to control their risk-taking because their cognitive-control system has matured enough to the point where it can control the socioemotional network, even in the context of high arousal or when psychosocial capacities are present. Also, adults are less likely to find themselves in situations that push them to do risky things. For example, teens are more likely to be around peers who peer pressure them into doing things, while adults are not as exposed to this sort of social setting. == Cognitive and personal biases == Biases usually affects decision-making processes. They appear more when decision task has time pressure, is done under high stress and/or are highly complex. Here is a list of commonly debated biases in judgment and decision-making: Selective search for evidence (also known as confirmation bias): People tend to be willing to gather facts that support certain conclusions but disregard other facts that support different conclusions. Individuals who are highly defensive in this manner show significantly greater left prefrontal cortex activity as measured by EEG than do less defensive individuals. Premature termination of search for evidence: People tend to accept the first alternative that looks like it might


id: decision-making-20260505-5
file: data/en.wikipedia.org/wiki/Decision-making-5.md
category: reference
title: Decision-making
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Decision-making
date_saved: 2026-05-05T11:04:22.741043+00:00
instance: kb-cron
parent: decision-making-20260505-0
summary:
The psychologist Daniel Kahneman, adopting terms originally proposed by the psychologists Keith Stanovich and Richard West, has theorized that a person's decision-making is the result of an interplay between two kinds of cognitive processes: an automatic intuitive system (called "System 1") and an effortful rational system (called "System 2"). System 1 is a bottom-up, fast, and implicit system of decision-making, while system 2 is a top-down, slow, and explicit system of decision-making. System 1 includes simple heuristics in judgment and decision-making such as the affect heuristic, the availability heuristic, the familiarity heuristic, and the representativeness heuristic. === Combinatorial vs. positional === Styles and methods of decision-making were elaborated by Aron Katsenelinboigen, the founder of predispositioning theory. In his analysis of styles and methods, Katsenelinboigen referred to the game of chess, saying that "chess does disclose various methods of operation, notably the creation of predisposition methods which may be applicable to other, more complex systems." Katsenelinboigen states that apart from the methods (reactive and selective) and sub-methods randomization, predispositions, programming), there are two major styles: positional and combinational. Both styles are utilized in the game of chess. The two styles reflect two basic approaches to uncertainty: deterministic (combinational style) and indeterministic


id: emotion-and-memory-20260505-0
file: data/en.wikipedia.org/wiki/Emotion_and_memory-0.md
category: reference
title: Emotion and memory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Emotion_and_memory
date_saved: 2026-05-05T11:04:24.054436+00:00
instance: kb-cron
parent: emotion-and-memory-20260505-0
summary:
Emotion can have a powerful effect on humans and animals. Numerous studies have shown that the most vivid autobiographical memories tend to be of emotional events, which are likely to be recalled more often and with more clarity and detail than neutral events. The activity of emotionally enhanced memory retention can be linked to human evolution; during early development, responsive behavior to environmental events would have progressed as a process of trial and error. Survival depended on behavioral patterns that were repeated or reinforced through life and death situations. Through evolution, this process of learning became genetically embedded in humans and all animal species in what is known as flight or fight instinct. Artificially inducing this instinct through traumatic physical or emotional stimuli essentially creates the same physiological condition that heightens memory retention by exciting neuro-chemical activity affecting areas of the brain responsible for encoding and recalling memory. This memory-enhancing effect of emotion has been demonstrated in many laboratory studies, using stimuli ranging from words to pictures to narrated slide shows, as well as autobiographical memory studies. However, as described below, emotion does not always enhance memory. == Arousal and valence in memory == One of the most common frameworks


id: emotion-and-memory-20260505-1
file: data/en.wikipedia.org/wiki/Emotion_and_memory-1.md
category: reference
title: Emotion and memory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Emotion_and_memory
date_saved: 2026-05-05T11:04:24.054436+00:00
instance: kb-cron
parent: emotion-and-memory-20260505-0
summary:
==== Prioritized processing ==== Emotional items also appear more likely to be processed when attention is limited, suggesting a facilitated or prioritized processing of emotional information. This effect was demonstrated using the attentional blink paradigm in which 2 target items are presented in close temporal proximity within a stream of rapidly presented stimuli. The typical finding is that participants often miss the second target item, as if there were a "blink" of attention following the first target's presentation, reducing the likelihood that the second target stimulus is attended. However, when the second target stimulus elicits emotional arousal (a "taboo" word), participants are less likely to miss the target's presentation, which suggests that under conditions of limited attention, arousing items are more likely to be processed than neutral items. Additional support for the prioritized processing hypothesis was provided by studies investigating the visual extinction deficit. People suffering from this deficit can perceive a single stimulus in either side visual field if it is presented alone but are unaware of the same stimulus in the visual field opposed to the lesional side, if another stimulus is presented simultaneously on the lesional side. Emotion has been found to modulate the magnitude of the


id: emotion-and-memory-20260505-2
file: data/en.wikipedia.org/wiki/Emotion_and_memory-2.md
category: reference
title: Emotion and memory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Emotion_and_memory
date_saved: 2026-05-05T11:04:24.054436+00:00
instance: kb-cron
parent: emotion-and-memory-20260505-0
summary:
==== Contextual effects of emotion on memory ==== Contextual effects occur as a result of the degree of similarity between the encoding context and the retrieval context of an emotional dimension. The main findings are that the current mood we are in affects what is attended, encoded and ultimately retrieved, as reflected in two similar but subtly different effects: the mood congruence effect and mood-state dependent retrieval. Positive encoding contexts have been connected to activity in the right fusiform gyrus. Negative encoding contexts have been correlated to activity in the right amygdala (Lewis & Critchley, 2003). However, Lewis and Critchley (2003) claim that it is not clear whether involvement of the emotional system in encoding memory differs for positive or negative emotions, or whether moods at recall lead to activity in the corresponding positive or negative neural networks. ===== Mood congruence effect ===== The mood congruence effect refers to the tendency of individuals to retrieve information more easily when it has the same emotional content as their current emotional state. For instance, being in a depressed mood increases the tendency to remember negative events (Drace, 2013). This effect has been demonstrated for explicit retrieval as well as implicit retrieval. =====


id: emotion-and-memory-20260505-3
file: data/en.wikipedia.org/wiki/Emotion_and_memory-3.md
category: reference
title: Emotion and memory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Emotion_and_memory
date_saved: 2026-05-05T11:04:24.054436+00:00
instance: kb-cron
parent: emotion-and-memory-20260505-0
summary:
== Neurobiological mechanisms of emotional memory enhancement == The neural mechanism underlying emotional memory enhancement involves the interaction between the amygdala and the hippocampus, as well as several other factors that prioritize the encoding of emotional experiences. When an emotional experience occurs, the amygdala becomes highly active, signaling the hippocampus to strengthen the encoding and consolidation of these memories. This process is facilitated by the release of stress hormones and neurotransmitters, which modulate synaptic plasticity and enhance neural connectivity. Multiple mechanisms have been proposed to explain this prioritized encoding, including the neuromodulatory effects on plasticity and the dynamic interplay between the amygdala and the hippocampus. Intracranial EEG studies have shown that the amygdala triggers pronounced hippocampal sharp-wave ripples after encoding emotional experiences, further reinforcing the consolidation of these memories during both awake and sleep. This coordinated activity between the amygdala and hippocampus ensures that emotionally significant events are prioritized in long-term memory storage, leveraging both immediate neurochemical changes and enduring structural adaptations in neural circuits. == Memory of felt emotion == Many researchers use self-report measures of felt emotion as a manipulation check. This raises an interesting question and a possible methodological weakness: are people always accurate when they recall


id: emotion-and-memory-20260505-4
file: data/en.wikipedia.org/wiki/Emotion_and_memory-4.md
category: reference
title: Emotion and memory
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Emotion_and_memory
date_saved: 2026-05-05T11:04:24.054436+00:00
instance: kb-cron
parent: emotion-and-memory-20260505-0
summary:
== Emotion regulation effects on memory == An interesting issue in the study of the emotion-memory relationship is whether our emotions are influenced by our behavioral reaction to them, and whether this reaction—in the form of expression or suppression of the emotion—might affect what we remember about an event. Researchers have begun to examine whether concealing feelings influences our ability to perform common cognitive tasks, such as forming memories, and found that the emotion regulation efforts do have cognitive consequences. In the seminal work on negative affect arousal and white noise, Seidner found support for the existence of a negative affect arousal mechanism through observations regarding the devaluation of speakers from other ethnic origins." In a study of Richards and Gross (1999) and Tiwari (2013), participants viewed slides of injured men that produced increases in negative emotions, while information concerning each man was presented orally with his slide. The participants were assigned to either an expressive suppression group (where they were asked to refrain from showing emotion while watching the slides) or to a control group (where they were not given regulatory instructions at all). As predicted by the researchers, suppressors showed significantly worse performance on a memory test for


id: encephalitis-lethargica-20260505-0
file: data/en.wikipedia.org/wiki/Encephalitis_lethargica-0.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:
Encephalitis lethargica (EL) is an atypical form of encephalitis. Also known as "von Economo Encephalitis", "sleeping sickness" or "sleepy sickness" (distinct from tsetse fly–transmitted sleeping sickness), it was first described in 1917 by neurologist Constantin von Economo and pathologist Jean-René Cruchet. The disease attacks the brain, leaving some victims in a statue-like condition, speechless and motionless. Between 1915 and 1926, an epidemic of encephalitis lethargica spread around the world. The exact number of people infected is unknown, but it is estimated that more than one million people contracted the disease during the epidemic, which directly caused more than 500,000 deaths. Most of those who survived never recovered their pre-morbid vigor. == Signs and symptoms == Encephalitis lethargica is characterized by high fever, sore throat, headache, lethargy, double vision, delayed physical and mental response, sleep inversion and catatonia. In severe cases, patients may enter a coma-like state (akinetic mutism). Patients may also experience abnormal eye movements ("oculogyric crises"), Parkinsonism, upper body weakness, muscular pains, tremors, neck rigidity, and behavioral changes including psychosis. Klazomania, a vocal tic involving compulsive screaming, is sometimes present. Approximately a third of the affected children experienced change of behavior, with many of them becoming "delinquents". Boys between


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: 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: 2026-05-05T11:04:42.322703+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: 2026-05-05T11:04:42.322703+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: 2026-05-05T11:04:42.322703+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: 2026-05-05T11:04:42.322703+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: 2026-05-05T11:04:42.322703+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: 2026-05-05T11:04:42.322703+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: 2026-05-05T11:04:42.322703+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: 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


