# kb

id: night-20260505-1
file: data/en.wikipedia.org/wiki/Night-1.md
category: reference
title: Night
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Night
date_saved: 2026-05-05T11:13:01.139082+00:00
instance: kb-cron
parent: night-20260505-0
summary:
The length of night on Earth varies depending on the time of year. Longer nights occur in winter, with the winter solstice being the longest. Nights are shorter in the summer, with the summer solstice being the shortest. Earth orbits the Sun on an axis tilted 23.44 degrees. Nights are longer when a hemisphere is tilted away from the Sun and shorter when a hemisphere is tilted toward the Sun. As a result, the longest night of the year for the Northern Hemisphere will be the shortest night of the year for the Southern Hemisphere. Night's duration varies least near the equator. The difference between the shortest and longest night increases approaching the poles. At the equator, night lasts roughly 12 hours throughout the year. The tropics have little difference in the length of day and night. At the 45th parallel, the longest winter night is roughly twice as long as the shortest summer night. Within the polar circles, night will last the full 24 hours of the winter solstice. The length of this polar night increases closer to the poles. Utqiagvik, Alaska, the northernmost point in the United States, experiences 65 days of polar night. At the pole itself,


id: night-20260505-2
file: data/en.wikipedia.org/wiki/Night-2.md
category: reference
title: Night
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Night
date_saved: 2026-05-05T11:13:01.139082+00:00
instance: kb-cron
parent: night-20260505-0
summary:
Living organisms react directly to the darkness of night. Light and darkness also affect circadian rhythms, the physical and mental changes that occur in a 24-hour cycle. This daily cycle is regulated by an internal "biological clock" that is adjusted by exposure to light. The length and timing of nighttime depend on location and time of year. Organisms that are more active at night possess adaptations to the night's dimmer light, increased humidity, and lower temperatures. === Animals === Animals that are active primarily at night are called nocturnal and usually possess adaptations for night vision. In vertebrates' eyes, two types of photoreceptor cells sense light. Cone cells sense color but are ineffective in low light; rod cells sense only brightness but remain effective in very dim light. The eyes of nocturnal animals have a greater percentage of rod cells. In most mammals, rod cells contain densely packed DNA near the edge of the nucleus. For nocturnal mammals, this is reversed with the densely packed DNA in the center of the nucleus, which reduces the scattering of light. Some nocturnal animals have a mirror, the tapetum lucidum, behind the retina. This doubles the amount of light their eyes can process.


id: night-20260505-3
file: data/en.wikipedia.org/wiki/Night-3.md
category: reference
title: Night
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Night
date_saved: 2026-05-05T11:13:01.139082+00:00
instance: kb-cron
parent: night-20260505-0
summary:
During the day, plants engage in photosynthesis and release oxygen. By night, plants engage in respiration, consuming oxygen and releasing carbon dioxide. Plants can draw up more water after sunset, which facilitates new leaf growth. As plants cannot create energy through photosynthesis after sunset, they use energy stored in the plant, typically as starch granules. Plants use this stored energy at a steady rate, depleting their reserves almost right at dawn. Plants will adjust their rate of consumption to match the expected time until sunrise. This avoids prematurely running out of starch reserves, and it allows the plant to adjust for longer nights in the winter. If a plant is subjected to artificially early darkness, it will ration its energy consumption to last until dawn. Succulent plants, including cacti, have adapted to the limited water availability in arid environments like deserts. The stomata of cacti do not open until night. When the temperature drops, the pores open to allow the cacti to store carbon dioxide for photosynthesis the next day, a process known as crassulacean acid metabolism (CAM). Cacti and night-blooming plants use CAM to store up to 99% of the carbon dioxide they use in daily photosynthesis. Ceroid cacti


id: night-20260505-4
file: data/en.wikipedia.org/wiki/Night-4.md
category: reference
title: Night
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Night
date_saved: 2026-05-05T11:13:01.139082+00:00
instance: kb-cron
parent: night-20260505-0
summary:
Artificial lighting expanded the scope of acceptable work and leisure after dark. In the 1600s, the major European cities introduced streetlights. These were lit by lamplighters each evening outside of the summer months. Early streetlights were metal and glass enclosures housing candles or oil lamps. They were suspended above streets or mounted on posts. The use of artificial lighting led to an increase in acceptable nightlife. In more rural areas, night remained a period of rest and nocturnal labor. Young adults, the urban poor, prostitutes, and thieves benefited from the anonymity of darkness and frequently smashed the new lanterns. Gas lighting was invented in the 1800s. A gas mantle was over ten times brighter than an oil lamp. Gas lighting was associated with the creation of regular police forces. In England, police departments were tasked with maintaining the gas lights, which became known as "police lamps". Daytime routines were further pushed back into the night by the electric light bulb—invented in the late 19th century—and the widespread usage of newer timekeeping devices like watches. Electric lights created night shifts for traditionally daytime fields, like India's cotton industry, and created opportunities for working adults to attend night school. === Fear of


id: night-20260505-5
file: data/en.wikipedia.org/wiki/Night-5.md
category: reference
title: Night
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Night
date_saved: 2026-05-05T11:13:01.139082+00:00
instance: kb-cron
parent: night-20260505-0
summary:
Many times in the night season, there have been certain spirits heard softly going or spitting or groaning, who being asked what they were have made answer that they were the souls of this or that man and that they now endure extreme torments. In folklore, nocturnal preternatural beings like goblins, fairies, werewolves, pucks, brownies, banshees, and boggarts have overlapping but non-synonymous definitions. The werewolf—and its francophone variations, the loup-garou and rougarou—were believed to be people who transformed into beasts at night. In West Africa and among the African diaspora, there is a widespread tradition of a type of vampire who removes their human skin at night and travels as a blood-sucking ball of light. Variation includes the feu-follet, the Surinamese asema, the Caribbean sukuyan, the Ashanti obayifo, and the Ghanaian asanbosam. The medieval fear of night-flying European witches was influenced by the Roman strix. The Romans described the strix as capable of changing between a beautiful woman and an owl-shaped monster. Common themes among these mythical nocturnal entities include hypersexuality, predation, shapeshifting, deception, mischief, and malice. === Nightlife === Nightlife, sometimes referred to as "the night-time economy", is a range of entertainment available and generally more popular from the


id: night-20260505-6
file: data/en.wikipedia.org/wiki/Night-6.md
category: reference
title: Night
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Night
date_saved: 2026-05-05T11:13:01.139082+00:00
instance: kb-cron
parent: night-20260505-0
summary:
Night photography can capture the natural colors of night by increasing the exposure time, or length of time captured in the photography. Longer exposures open the possibility for photographers to use light painting to selectively illuminate a scene. Digital photography can also make use of high-ISO settings, which increase the sensitivity to light, to take shorter exposure shots. This makes it possible to capture moving subjects without turning their movements into a blur. === Painting === Dating back to prehistoric cave paintings, artists have used a range of symbols to denote and depict the night sky. The first widely accepted portrayal of the night sky is the Nebra sky disc created c. 1600 BC. In medieval art, astrological signs gave meaning to paintings of night scenes. Adam Elsheimer's paintings on copper plates were some of the earliest realistic depictions of the night sky. Baroque paintings typically used a darker color scheme than previous painting styles in Europe. From the 17th century, darkness took up larger areas of paintings on average. Changes in the chemical composition of the paint itself and the development of new techniques for representing light led to the tenebrism style of painting. Tenebrism used stark, realistic depictions


id: noon-20260505-0
file: data/en.wikipedia.org/wiki/Noon-0.md
category: reference
title: Noon
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Noon
date_saved: 2026-05-05T11:13:02.309491+00:00
instance: kb-cron
parent: noon-20260505-0
summary:
Noon (also known as noontime or midday) is 12 o'clock in the daytime. Solar noon is the time when the Sun appears to contact the local celestial meridian. This is when the Sun reaches its apparent highest point in the sky, at 12 noon apparent solar time and can be observed using a sundial. The local or clock time of solar noon depends on the date, longitude, and time zone, with Daylight Saving Time tending to place solar noon closer to 1:00pm. == Etymology == The word noon is derived from Latin nona hora, the ninth canonical hour of the day, in reference to the Western Christian liturgical term Nones, (number nine), one of the seven fixed prayer times in traditional Christian denominations. The Roman and Western European medieval monastic day began at 6:00 a.m. (06:00) at the equinox by modern timekeeping, so the ninth hour ended at what is now 3:00 p.m. (15:00) at the equinox. In English, the meaning of the word shifted to midday and the time gradually moved back to 12:00 local time – that is, not taking into account the modern invention of time zones. The change began in the 12th century and was fixed


id: octaeteris-20260505-0
file: data/en.wikipedia.org/wiki/Octaeteris-0.md
category: reference
title: Octaeteris
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Octaeteris
date_saved: 2026-05-05T11:13:03.509120+00:00
instance: kb-cron
parent: octaeteris-20260505-0
summary:
In astronomy, an octaeteris (Greek: ὀκταετηρίς, plural: octaeterides) is the period of eight solar years after which the moon phase occurs on the same day of the year plus one or two days. This period is also in a very good synchronicity with five Venusian visibility cycles (the Venusian synodic period) and thirteen Venusian revolutions around the Sun (Venusian sidereal period). This means, that if Venus is visible beside the Moon, after eight years the two will be again close together near the same date of the calendar. The octaeteris, also known as oktaeteris, was noted by Cleostratus in ancient Greece as a ⁠2 923+ 1 /2⁠ day cycle. The octaeteris is the calendar used for the Olympic games; if one Olympiad was 50 months long, the next would be 49 lunar months long. This octaeteris calendar is used for the Olympic dial of the Antikythera mechanism, to determine the time of the Olympic games and other Greek festivities. == See also == Metonic cycle Eclipse cycle == References == Meeus, Jean (1997). Mathematical Astronomy Morsels. Willmann-Bell. Chapter 9, p. 51, Table 9.A "Some eclipse Periodicities".


id: orbital-period-20260505-0
file: data/en.wikipedia.org/wiki/Orbital_period-0.md
category: reference
title: Orbital period
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Orbital_period
date_saved: 2026-05-05T11:13:04.738684+00:00
instance: kb-cron
parent: orbital-period-20260505-0
summary:
The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets, exoplanets orbiting other stars, or binary stars. It may also refer to the time it takes a satellite orbiting a planet or moon to complete one orbit. For celestial objects in general, the orbital period is determined by a 360° revolution of one body around its primary, e.g. Earth around the Sun. Periods in astronomy are expressed in units of time, usually hours, days, or years. Its reciprocal is the orbital frequency, a kind of revolution frequency, in units of hertz. == Small body orbiting a central body == According to Kepler's Third Law, the orbital period T of two point masses orbiting each other in a circular or elliptic orbit is: T = 2 π a 3 G M {\displaystyle T=2\pi {\sqrt {\frac {a^{3}}{GM}}}} where: a is the orbit's semi-major axis G is the gravitational constant, M is the mass of the more massive body. For all ellipses with a given semi-major axis the orbital period is the same, regardless of


id: orbital-period-20260505-1
file: data/en.wikipedia.org/wiki/Orbital_period-1.md
category: reference
title: Orbital period
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Orbital_period
date_saved: 2026-05-05T11:13:04.738684+00:00
instance: kb-cron
parent: orbital-period-20260505-0
summary:
For celestial objects in general, the orbital period typically refers to the sidereal period, determined by a 360° revolution of one body around its primary relative to the fixed stars projected in the sky. For the case of the Earth orbiting around the Sun, this period is referred to as the sidereal year. This is the orbital period in an inertial (non-rotating) frame of reference. Orbital periods can be defined in several ways. The tropical period is more particularly about the position of the parent star. It is the basis for the solar year, and respectively the calendar year. The synodic period refers not to the orbital relation to the parent star, but to other celestial objects, making it not a merely different approach to the orbit of an object around its parent, but a period of orbital relations with other objects, normally Earth, and their orbits around the Sun. It applies to the elapsed time where planets return to the same kind of phenomenon or location, such as when any planet returns between its consecutive observed conjunctions with or oppositions to the Sun. For example, Jupiter has a synodic period of 398.8 days from Earth; thus, Jupiter's opposition occurs


id: ramesside-star-clocks-20260505-0
file: data/en.wikipedia.org/wiki/Ramesside_star_clocks-0.md
category: reference
title: Ramesside star clocks
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Ramesside_star_clocks
date_saved: 2026-05-05T11:13:05.928376+00:00
instance: kb-cron
parent: ramesside-star-clocks-20260505-0
summary:
The Ramesside star clocks are ancient Egyptian star clocks appearing on the ceilings of several royal tombs of the Ramesside period. Two sets of star clocks appear on the tomb Ramesses VII and Ramesses IX. Although all of the sets are corrupt to some degree, a prototype clock can be reconstructed from them. == References ==


id: relative-hour-20260505-0
file: data/en.wikipedia.org/wiki/Relative_hour-0.md
category: reference
title: Relative hour
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Relative_hour
date_saved: 2026-05-05T11:13:07.167936+00:00
instance: kb-cron
parent: relative-hour-20260505-0
summary:
Relative hour (Hebrew singular: shaʿah zǝmanit / שעה זמנית; plural: shaʿot - zǝmaniyot / שעות זמניות), sometimes called halachic hour, temporal hour, seasonal hour and variable hour, is a term used in rabbinic Jewish law that assigns 12 hours to each day and 12 hours to each night, all throughout the year. A relative hour has no fixed length in absolute time, but changes with the length of daylight each day - depending on summer (when the days are long and the nights are short), and in winter (when the days are short and the nights are long). Even so, in all seasons a day is always divided into 12 hours, and a night is always divided into 12 hours, which invariably makes for a longer hour or a shorter hour. At Mediterranean latitude, one hour can be about 45 minutes at the winter solstice, and 75 minutes at summer solstice. All of the hours mentioned by the Sages in either the Mishnah or Talmud, or in other rabbinic writings, refer strictly to relative hours. Another feature of this ancient practice is that, unlike the standard modern 12-hour clock that assigns 12 o'clock pm for noon time, in the ancient


id: relative-hour-20260505-1
file: data/en.wikipedia.org/wiki/Relative_hour-1.md
category: reference
title: Relative hour
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Relative_hour
date_saved: 2026-05-05T11:13:07.167936+00:00
instance: kb-cron
parent: relative-hour-20260505-0
summary:
=== Disputations === In old times, the hour was detected by observation of the position of the sun, or when the first three stars appeared in the night sky. During the first six hours of the day, the sun is seen in the eastern sky. At the sixth hour, the sun is always at its zenith in the sky, meaning, it is either directly overhead, or parallel (depending on the hemisphere). Those persons living in the Northern Hemisphere, the sun at noon time will appear overhead slightly towards the south, whereas for those living in the Southern Hemisphere, the sun at noon time will appear overhead slightly towards the north (an exception being in the tropics, the sun can sometimes be directly overhead). From the 6th and a half hour to the 12th hour, the sun inclines towards the west, until it sets. The conclusion of a day at the end of twilight may slightly vary in minutes from place to place, depending on the elevation and the terrain. Typically, nightfall ushers in more quickly in the low-lying valleys, than it does on a high mountaintop. There are two major opinions how to calculate these times: The Magen Avraham (Shulhan


id: relative-hour-20260505-2
file: data/en.wikipedia.org/wiki/Relative_hour-2.md
category: reference
title: Relative hour
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Relative_hour
date_saved: 2026-05-05T11:13:07.167936+00:00
instance: kb-cron
parent: relative-hour-20260505-0
summary:
== Practical bearing == In Jewish Halacha, the practical bearing of this teaching is reflected in many halachic practices. For example, according to Jewish law, the morning recitation of Kriyat Shema must be made between slightly before sunrise and the end of the third hour of the day, a time that actually fluctuates on the standard 12-hour clock, depending on the time of year. Its application is also used in determining the time of the Morning Prayer, which must be recited between sunrise until the end of the fourth hour, but post facto can be said until noon time, and which times will vary if one were to rely solely on the dials of the standard 12-hour clock, depending on the seasons. On the eve of Passover, chametz can only be eaten until the end of the fourth-hour of the day, and must be disposed of by the end of the fifth hour. In Jewish tradition, prayers were usually offered at the time of the daily whole-burnt offerings. The historian, Josephus, writing about the daily whole-burnt offering, says that it was offered twice each day, in the morning and about the ninth hour. The Mishnah, a compendium of Jewish oral


id: relaxation-physics-20260505-0
file: data/en.wikipedia.org/wiki/Relaxation_(physics)-0.md
category: reference
title: Relaxation (physics)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Relaxation_(physics)
date_saved: 2026-05-05T11:13:24.533010+00:00
instance: kb-cron
parent: relaxation-physics-20260505-0
summary:
In the physical sciences, relaxation usually means the return of a perturbed system into equilibrium. Each relaxation process can be categorized by a relaxation time τ. The simplest theoretical description of relaxation as function of time t is an exponential law exp(−t/τ) (exponential decay). == In simple linear systems == === Mechanics: Damped unforced oscillator === Let the homogeneous differential equation: m d 2 y d t 2 + γ d y d t + k y = 0 {\displaystyle m{\frac {d^{2}y}{dt^{2}}}+\gamma {\frac {dy}{dt}}+ky=0} model damped unforced oscillations of a weight on a spring. The displacement will then be of the form y ( t ) = A e − t / T cos ⁡ ( μ t − δ ) {\displaystyle y(t)=Ae^{-t/T}\cos(\mu t-\delta )} . The constant T ( = 2 m / γ {\displaystyle =2m/\gamma } ) is called the relaxation time of the system and the constant μ is the quasi-frequency. === Electronics: RC circuit === In an RC circuit containing a charged capacitor and a resistor, the voltage decays exponentially: V ( t ) = V 0 e − t R C , {\displaystyle V(t)=V_{0}e^{-{\frac {t}{RC}}}\ ,} The constant τ = R C {\displaystyle \tau =RC\


id: relaxation-physics-20260505-1
file: data/en.wikipedia.org/wiki/Relaxation_(physics)-1.md
category: reference
title: Relaxation (physics)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Relaxation_(physics)
date_saved: 2026-05-05T11:13:24.533010+00:00
instance: kb-cron
parent: relaxation-physics-20260505-0
summary:
This equation can be solved by substitution to yield [ A ] = k ′ − k e − ( k + k ′ ) t k + k ′ [ A ] 0 {\displaystyle {\ce {[A]}}={k'-ke^{-(k+k')t} \over k+k'}{\ce {[A]}}_{0}} == In atmospheric sciences == === Desaturation of clouds === Consider a supersaturated portion of a cloud. Then shut off the updrafts, entrainment, and any other vapor sources/sinks and things that would induce the growth of the particles (ice or water). Then wait for this supersaturation to reduce and become just saturation (relative humidity = 100%), which is the equilibrium state. The time it takes for the supersaturation to dissipate is called relaxation time. It will happen as ice crystals or liquid water content grow within the cloud and will thus consume the contained moisture. The dynamics of relaxation are very important in cloud physics for accurate mathematical modelling. In water clouds where the concentrations are larger (hundreds per cm3) and the temperatures are warmer (thus allowing for much lower supersaturation rates as compared to ice clouds), the relaxation times will be very low (seconds to minutes). In ice clouds the concentrations are lower (just a few per liter) and


id: rotation-period-astronomy-20260505-0
file: data/en.wikipedia.org/wiki/Rotation_period_(astronomy)-0.md
category: reference
title: Rotation period (astronomy)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Rotation_period_(astronomy)
date_saved: 2026-05-05T11:13:25.739752+00:00
instance: kb-cron
parent: rotation-period-astronomy-20260505-0
summary:
In astronomy, the rotation period or spin period of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the sidereal rotation period (or sidereal day), i.e., the time that the object takes to complete a full rotation around its axis relative to the background stars (inertial space). The other type of commonly used "rotation period" is the object's synodic rotation period (or solar day), which may differ, by a fraction of a rotation or more than one rotation, to accommodate the portion of the object's orbital period around a star or another body during one day. == Measuring rotation == For solid objects, such as rocky planets and asteroids, the rotation period is a single value. For gaseous or fluid bodies, such as stars and giant planets, the period of rotation varies from the object's equator to its pole due to a phenomenon called differential rotation. Typically, the stated rotation period for a giant planet (such as Jupiter, Saturn, Uranus, Neptune) is its internal rotation period, as determined from the rotation of the planet's magnetic field. For objects that are not spherically symmetrical, the rotation period is, in general, not fixed, even in


id: saros-astronomy-20260505-0
file: data/en.wikipedia.org/wiki/Saros_(astronomy)-0.md
category: reference
title: Saros (astronomy)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Saros_(astronomy)
date_saved: 2026-05-05T11:13:27.065142+00:00
instance: kb-cron
parent: saros-astronomy-20260505-0
summary:
In astronomy, the saros ( ) is a length of time covering exactly 223 synodic months (18 years 11 days and 8 hours), 242 draconic months and 239 anomalistic months. Arising naturally due to synchronization between lunar phase, nodal precession, and apsidal precession, it can be used to predict eclipses of the Sun and Moon. One saros period after an eclipse, the Sun, Earth, and Moon return to approximately the same relative geometry, a near straight line, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle. Every eclipse has an associated saros series and all succeeding or preceding eclipses have a different saros series associated with them - as the eclipse of the same series occurs or occurred with a gap of one saros only. Solar and lunar eclipses have different saros series. A series of eclipses that are separated by one saros is called a saros series. It corresponds to: 6,585.321347 solar days 18.029 years 223 synodic months 241.999 draconic months 18.999 eclipse years (38 eclipse seasons of 173.31 days) 238.992 anomalistic months 241.029 sidereal months The 19 eclipse years means that if there is a solar eclipse (or lunar eclipse), then


id: saros-astronomy-20260505-1
file: data/en.wikipedia.org/wiki/Saros_(astronomy)-1.md
category: reference
title: Saros (astronomy)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Saros_(astronomy)
date_saved: 2026-05-05T11:13:27.065142+00:00
instance: kb-cron
parent: saros-astronomy-20260505-0
summary:
After one saros, the Moon will have completed roughly an integer number of synodic, draconic, and anomalistic periods (223, 242, and 239) and the Earth-Sun-Moon geometry will be nearly identical: the Moon will have the same phase and be at the same node and the same distance from the Earth. In addition, because the saros is close to 18 years in length (about 11 days longer), the Earth will be nearly the same distance from the Sun, and tilted to it in nearly the same orientation (same season). Given the date of an eclipse, one saros later a nearly identical eclipse can be predicted. During this 18-year period, about 40 other solar and lunar eclipses take place, but with a somewhat different geometry. One saros equaling 18.03 years is not equal to a perfect integer number of lunar orbits (Earth revolutions with respect to the fixed stars of 27.32166 days sidereal month), therefore, even though the relative geometry of the Earth–Sun–Moon system will be nearly identical after a saros, the Moon will be in a slightly different position with respect to the stars for each eclipse in a saros series. The axis of rotation of the Earth–Moon system exhibits a


id: saros-astronomy-20260505-2
file: data/en.wikipedia.org/wiki/Saros_(astronomy)-2.md
category: reference
title: Saros (astronomy)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Saros_(astronomy)
date_saved: 2026-05-05T11:13:27.065142+00:00
instance: kb-cron
parent: saros-astronomy-20260505-0
summary:
As an example of a single saros series, this table gives the dates of some of the 72 lunar eclipses for saros series 131. This eclipse series began in AD 1427 with a partial eclipse at the southern edge of the Earth's shadow when the Moon was close to its descending node. In each successive saros, the Moon's orbital path is shifted northward with respect to the Earth's shadow, with the first total eclipse occurring in 1950. For the following 252 years, total eclipses occur, with the central eclipse in 2078. The first partial eclipse after this will occur in the year 2220, and the final partial eclipse of the series will occur in 2707. The total lifetime of lunar saros series 131 is 1280 years. Solar saros 138 interleaves with this lunar saros with an event occurring every 9 years 5 days alternating between each saros series. Because of the +1⁄3 fraction of days in a saros, the visibility of each eclipse will differ for an observer at a given locale. For the lunar saros series 131, the first total eclipse of 1950 had its best visibility for viewers in Eastern Europe and the Middle East because mid-eclipse was


id: sidereal-time-20260505-0
file: data/en.wikipedia.org/wiki/Sidereal_time-0.md
category: reference
title: Sidereal time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Sidereal_time
date_saved: 2026-05-05T11:13:28.221801+00:00
instance: kb-cron
parent: sidereal-time-20260505-0
summary:
Sidereal time ("sidereal" pronounced sy-DEER-ee-əl, sə-) is a system of timekeeping used especially by astronomers. Using sidereal time and the celestial coordinate system, it is easy to locate the positions of celestial objects in the night sky. Sidereal time is a "time scale that is based on Earth's rate of rotation measured relative to the fixed stars". A sidereal day (also known as the sidereal rotation period) represents the time for one rotation about the planet axis relative to the stars. Viewed from the same location, a star seen at one position in the sky will be seen at the same position on another night at the same time of day (or night), if the day is defined as a sidereal day. This is similar to how the time kept by a sundial (Solar time) can be used to find the location of the Sun. Just as the Sun and Moon appear to rise in the east and set in the west due to the rotation of Earth, so do the stars. Both solar time and sidereal time make use of the regularity of Earth's rotation about its polar axis: solar time is reckoned according to the position of the


id: sidereal-time-20260505-1
file: data/en.wikipedia.org/wiki/Sidereal_time-1.md
category: reference
title: Sidereal time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Sidereal_time
date_saved: 2026-05-05T11:13:28.221801+00:00
instance: kb-cron
parent: sidereal-time-20260505-0
summary:
== Effects of precession == Earth's rotation is not a simple rotation around an axis that remains always parallel to itself. Earth's rotational axis itself rotates about a second axis, orthogonal to the plane of Earth's orbit, taking about 25,800 years to perform a complete rotation. This phenomenon is termed the precession of the equinoxes. Because of this precession, the stars appear to move around Earth in a manner more complicated than a simple constant rotation. For this reason, to simplify the description of Earth's orientation in astronomy and geodesy, it was conventional to chart the positions of the stars in the sky according to right ascension and declination, which are based on a frame of reference that follows Earth's precession, and to keep track of Earth's rotation, through sidereal time, relative to this frame as well. (The conventional reference frame, for purposes of star catalogues, was replaced in 1998 with the International Celestial Reference Frame, which is fixed with respect to extra-galactic radio sources. Because of the great distances, these sources have no appreciable proper motion.) In this frame of reference, Earth's rotation is close to constant, but the stars appear to rotate slowly with a period of about


id: sidereal-time-20260505-2
file: data/en.wikipedia.org/wiki/Sidereal_time-2.md
category: reference
title: Sidereal time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Sidereal_time
date_saved: 2026-05-05T11:13:28.221801+00:00
instance: kb-cron
parent: sidereal-time-20260505-0
summary:
=== Relationship between solar time and sidereal time intervals === If a certain interval I is measured in both mean solar time (UT1) and sidereal time, the numerical value will be greater in sidereal time than in UT1, because sidereal days are shorter than UT1 days. The ratio is: I m e a n s i d e r e a l I U T 1 = r ′ = 1.002 737 379 093 507 95 + 5.9006 × 10 − 11 t − 5.9 × 10 − 15 t 2 {\displaystyle {\frac {I_{\mathrm {mean\,sidereal} }}{I_{\mathrm {UT1} }}}=r'=1.002\,737\,379\,093\,507\,95+5.9006\times 10^{-11}t-5.9\times 10^{-15}t^{2}} such that t represents the number of Julian centuries elapsed since noon 1 January 2000 Terrestrial Time. == Sidereal days compared to solar days on other planets == Six of the eight solar planets have prograde rotation—that is, they rotate more than once per year in the same direction as they orbit the Sun, so the Sun rises in the east. Venus and Uranus, however, have retrograde rotation. For prograde rotation, the formula relating the lengths of the sidereal and solar days is: or, equivalently: When calculating the formula for a retrograde rotation, the operator of the denominator will be


id: solar-time-20260505-0
file: data/en.wikipedia.org/wiki/Solar_time-0.md
category: reference
title: Solar time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Solar_time
date_saved: 2026-05-05T11:13:29.423240+00:00
instance: kb-cron
parent: solar-time-20260505-0
summary:
Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Traditionally, there are three types of time reckoning based on astronomical observations: apparent solar time and mean solar time (discussed in this article), and sidereal time, which is based on the apparent motions of stars other than the Sun. == Introduction == A tall pole vertically fixed in the ground casts a shadow on any sunny day. At one moment during the day, the shadow will point exactly north or south (or disappear when and if the Sun moves directly overhead). That instant is called local apparent noon, or 12:00 local apparent time. About 24 hours later the shadow will again point north–south, the Sun seeming to have covered a 360-degree arc around Earth's axis. When the Sun has covered exactly 15 degrees (1/24 of a circle, both angles being measured in a plane perpendicular to Earth's axis), local apparent time is 13:00 exactly; after 15 more degrees it will be 14:00 exactly. The problem is that in September the Sun takes less time (as


id: solar-time-20260505-1
file: data/en.wikipedia.org/wiki/Solar_time-1.md
category: reference
title: Solar time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Solar_time
date_saved: 2026-05-05T11:13:29.423240+00:00
instance: kb-cron
parent: solar-time-20260505-0
summary:
The sun has always been visible in the sky, and its position forms the basis of apparent solar time, the timekeeping method used in antiquity. An Egyptian obelisk constructed c. 3500 BC, a gnomon in China dated 2300 BC, and an Egyptian sundial dated 1500 BC are some of the earliest methods for measuring the sun's position. Babylonian astronomers knew that the hours of daylight varied throughout the year. A tablet from 649 BC shows that they used a 2:1 ratio for the longest day to the shortest day, and estimated the variation using a linear zigzag function. It is not clear if they knew of the variation in the length of the solar day and the corresponding equation of time. Ptolemy clearly distinguishes the mean solar day and apparent solar day in his Almagest (2nd century), and he tabulated the equation of time in his Handy Tables. Apparent solar time grew less useful as commerce increased and mechanical clocks improved. Mean solar time was introduced in almanacs in England in 1834 and in France in 1835. Because the sun was difficult to observe directly due to its large size in the sky, mean solar time was determined as a


id: solstice-20260505-0
file: data/en.wikipedia.org/wiki/Solstice-0.md
category: reference
title: Solstice
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Solstice
date_saved: 2026-05-05T11:13:30.644057+00:00
instance: kb-cron
parent: solstice-20260505-0
summary:
A solstice is the time when the Sun reaches its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around 20–22 June and 20–22 December. In many countries, the seasons of the year are defined by reference to the solstices and the equinoxes. The term solstice can also be used in a broader sense, as the day when this occurs. For locations not too close to the equator or the poles, the dates with the longest and shortest periods of daylight are the summer and winter solstices, respectively. Terms with no ambiguity as to which hemisphere is the context are "June solstice" and "December solstice", referring to the months in which they take place every year. == Etymology == The word solstice is derived from the Latin sol ('sun') and sistere ('to stand still'), because at the solstices, the Sun's declination appears to "stand still"; that is, the seasonal movement of the Sun's daily path (as seen from Earth) reaches a northern or southern limit before reversing direction. Solstice first entered into English in the Middle English period. An older term in English is its calque sunstead (Old English: sunstede), which


id: solstice-20260505-1
file: data/en.wikipedia.org/wiki/Solstice-1.md
category: reference
title: Solstice
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Solstice
date_saved: 2026-05-05T11:13:30.644057+00:00
instance: kb-cron
parent: solstice-20260505-0
summary:
Also during the June solstice, places on the Arctic Circle (latitude 66.56° north) will see the Sun just on the horizon during midnight, and all places north of it will see the Sun above horizon for 24 hours. That is the midnight sun or midsummer-night sun or polar day. On the other hand, places on the Antarctic Circle (latitude 66.56° south) will see the Sun just on the horizon during midday, and all places south of it will not see the Sun above horizon at any time of the day. That is the polar night. During the December Solstice, the effects on both hemispheres are just the opposite. This sees polar sea ice re-grow annually due to lack of sunlight on the air above and surrounding sea. The warmest and coldest periods of the year in temperate regions are offset by about one month from the solstices, delayed by the earth's thermal inertia. == Cultural aspects == === Ancient Greek names and concepts === The concept of the solstices was embedded in ancient Greek celestial navigation. As soon as they discovered that the Earth was spherical they devised the concept of the celestial sphere, an imaginary spherical surface rotating with


id: solstice-20260505-2
file: data/en.wikipedia.org/wiki/Solstice-2.md
category: reference
title: Solstice
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Solstice
date_saved: 2026-05-05T11:13:30.644057+00:00
instance: kb-cron
parent: solstice-20260505-0
summary:
The term solstice can also be used in a wider sense, as the date (day) that such a passage happens. The solstices, together with the equinoxes, are connected with the seasons. In some languages they are considered to start or separate the seasons; in others they are considered to be centre points (in England, in the Northern Hemisphere, for example, the period around the northern solstice is known as midsummer). Midsummer's Day, defined as St. Johns Day by the Christian Church, is 24 June, about three days after the solstice itself). Similarly 25 December is the start of the Christmas celebration, and is the day the Sun begins to return to the Northern Hemisphere. The traditional British and Irish main rent and meeting days of the year, "the usual quarter days," were often those of the solstices and equinoxes. Many cultures celebrate various combinations of the winter and summer solstices, the equinoxes, and the midpoints between them, leading to various holidays arising around these events. During the southern or winter solstice, Christmas is the most widespread contemporary holiday, while Yalda, Saturnalia, Karachun, Hanukkah, Kwanzaa, and Yule are also celebrated around this time. In East Asian cultures, the Dongzhi Festival is


id: solstice-20260505-3
file: data/en.wikipedia.org/wiki/Solstice-3.md
category: reference
title: Solstice
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Solstice
date_saved: 2026-05-05T11:13:30.644057+00:00
instance: kb-cron
parent: solstice-20260505-0
summary:
=== Solstice determination === Unlike the equinox, the solstice time is not easy to determine. The changes in solar declination become smaller as the Sun gets closer to its maximum/minimum declination. The days before and after the solstice, the declination speed is less than 30 arcseconds per day which is less than 1⁄60 of the angular size of the Sun, or the equivalent to just 2 seconds of right ascension. This difference is hardly detectable with indirect viewing based devices like sextant equipped with a vernier, and impossible with more traditional tools like a gnomon or an astrolabe. It is also hard to detect the changes in sunrise/sunset azimuth due to the atmospheric refraction changes. Those accuracy issues render it impossible to determine the solstice day based on observations made within the 3 (or even 5) days surrounding the solstice without the use of more complex tools. Accounts do not survive but Greek astronomers must have used an approximation method based on interpolation, which is still used by some amateurs. This method consists of recording the declination angle at noon during some days before and after the solstice, trying to find two separate days with the same declination. When those


id: sunrise-equation-20260505-0
file: data/en.wikipedia.org/wiki/Sunrise_equation-0.md
category: reference
title: Sunrise equation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Sunrise_equation
date_saved: 2026-05-05T11:13:31.804583+00:00
instance: kb-cron
parent: sunrise-equation-20260505-0
summary:
The sunrise equation or sunset equation can be used to derive the time of sunrise or sunset for any solar declination and latitude in terms of local solar time when sunrise and sunset actually occur. == Geometric equation == The time at which a celestial object crosses the horizon can be calculated by converting its coordinates from the equatorial coordinate system to the horizontal coordinate system, and then solving the equation for an altitude of zero. We then obtain cos ⁡ H 0 = − tan ⁡ ϕ tan ⁡ δ {\displaystyle \cos H_{0}=-\tan \phi \,\tan \delta } where: H 0 {\displaystyle H_{0}} is the solar hour angle at either sunrise (when the negative value is taken) or sunset (when the positive value is taken); ϕ {\displaystyle \phi } is the latitude of the observer on the Earth; δ {\displaystyle \delta } is the Sun's declination. This gives the geometric rise or set time (ignoring refraction) of the center of the Sun. See below for an equation which accounts for these effects. The Earth rotates at an angular velocity of 15°/hour. Therefore, the expression H 0 / 15 ∘ {\displaystyle H_{0}/\mathrm {15} ^{\circ }} , where H 0 {\displaystyle H_{0}}


id: sunrise-equation-20260505-1
file: data/en.wikipedia.org/wiki/Sunrise_equation-1.md
category: reference
title: Sunrise equation
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Sunrise_equation
date_saved: 2026-05-05T11:13:31.804583+00:00
instance: kb-cron
parent: sunrise-equation-20260505-0
summary:
α 1 {\displaystyle \alpha _{1}} and δ 1 {\displaystyle \delta _{1}} , the right ascension and declination on day D − 1 {\displaystyle D-1} at 0h Universal Time, α 2 {\displaystyle \alpha _{2}} and δ 2 {\displaystyle \delta _{2}} , the right ascension and declination on day D {\displaystyle D} , α 3 {\displaystyle \alpha _{3}} and δ 3 {\displaystyle \delta _{3}} , the right ascension and declination on day D + 1 {\displaystyle D+1} . Calculate the approximate time of the sunset using cos ⁡ H 0 = sin ⁡ h 0 − sin ⁡ ϕ sin ⁡ δ 2 cos ⁡ ϕ cos ⁡ δ 2 . {\displaystyle \cos H_{0}={\dfrac {\sin h_{0}-\sin \phi \,\sin \delta _{2}}{\cos \phi \,\cos \delta _{2}}}.} If the right hand side has an absolute value greater than 1, then the Sun does not go below the horizon on that day and H 0 {\displaystyle H_{0}} does not exist. Calculate the transit, sunrise and sunset time in fractions of a day: m 0 = α 2 + L − θ 0 360 ∘ {\displaystyle m_{0}={\frac {\alpha _{2}+L-\theta _{0}}{360^{\circ }}}} m 1 = m 0 − H 0 360 ∘ {\displaystyle m_{1}=m_{0}-{\frac {H_{0}}{360^{\circ }}}} m 2


id: terrestrial-time-20260505-0
file: data/en.wikipedia.org/wiki/Terrestrial_Time-0.md
category: reference
title: Terrestrial Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Terrestrial_Time
date_saved: 2026-05-05T11:13:32.984785+00:00
instance: kb-cron
parent: terrestrial-time-20260505-0
summary:
Terrestrial Time (TT) is a modern astronomical time standard defined by the International Astronomical Union, primarily for time-measurements of astronomical observations made from the surface of Earth. For example, the Astronomical Almanac uses TT for its tables of positions (ephemerides) of the Sun, Moon and planets as seen from Earth. In this role, TT continues Terrestrial Dynamical Time (TDT or TD), which succeeded ephemeris time (ET). TT shares the original purpose for which ET was designed, to be free of the irregularities in the rotation of Earth. The unit of TT is the SI second, the definition of which is based currently on the caesium atomic clock, but TT is not itself defined by atomic clocks. It is a theoretical ideal, and real clocks can only approximate it. TT is distinct from the time scale often used as a basis for civil purposes, Coordinated Universal Time (UTC). TT is indirectly the basis of UTC, via International Atomic Time (TAI). Because of the historical difference between TAI and ET when TT was introduced, TT is 32.184 s ahead of TAI. == History == A definition of a terrestrial time standard was adopted by the International Astronomical Union (IAU) in 1976 at


id: terrestrial-time-20260505-1
file: data/en.wikipedia.org/wiki/Terrestrial_Time-1.md
category: reference
title: Terrestrial Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Terrestrial_Time
date_saved: 2026-05-05T11:13:32.984785+00:00
instance: kb-cron
parent: terrestrial-time-20260505-0
summary:
The main realization of TT is supplied by TAI. The BIPM TAI service, performed since 1958, estimates TT using measurements from an ensemble of atomic clocks spread over the surface and low orbital space of Earth. TAI is canonically defined retrospectively, in monthly bulletins, in relation to the readings shown by that particular group of atomic clocks at the time. Estimates of TAI are also provided in real time by the institutions that operate the participating clocks. Because of the historical difference between TAI and ET when TT was introduced, the TAI realization of TT is defined thus: T T ( T A I ) = T A I + 32.184 s . {\displaystyle \mathrm {TT(TAI)=TAI+32.184~s} .} The offset 32.184 s arises from history. The atomic time scale A1 (a predecessor of TAI) was set equal to UT2 at its conventional starting date of 1 January 1958, when ΔT (ET − UT) was about 32 seconds. The offset 32.184 seconds was the 1976 estimate of the difference between Ephemeris Time (ET) and TAI, "to provide continuity with the current values and practice in the use of Ephemeris Time". TAI is never revised once published and TT(TAI) has small errors relative


id: tropical-year-20260505-0
file: data/en.wikipedia.org/wiki/Tropical_year-0.md
category: reference
title: Tropical year
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tropical_year
date_saved: 2026-05-05T11:13:34.155727+00:00
instance: kb-cron
parent: tropical-year-20260505-0
summary:
A tropical year, or solar year (or tropical period), is the time that the Sun takes to return to the same position in the sky – as viewed from the Earth or another celestial body of the Solar System – thus completing a full cycle of astronomical seasons. For example, it is the time from vernal equinox to the next vernal equinox, or from summer solstice to the next summer solstice. It is the type of year used by tropical solar calendars. The tropical year is one type of astronomical year and a particular orbital period. Another type is the sidereal year (or sidereal orbital period), which is the time it takes Earth to complete one full orbit around the Sun as measured with respect to the fixed stars, resulting in a duration of 20 minutes and 24.7 seconds longer than the tropical year due to the precession of the equinoxes. Since antiquity, astronomers have progressively refined the definition of the tropical year. The entry for "year, tropical" in the Astronomical Almanac Online Glossary states: the period of time for the ecliptic longitude of the Sun to increase 360 degrees. Since the Sun's ecliptic longitude is measured with respect to


id: tropical-year-20260505-1
file: data/en.wikipedia.org/wiki/Tropical_year-1.md
category: reference
title: Tropical year
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tropical_year
date_saved: 2026-05-05T11:13:34.155727+00:00
instance: kb-cron
parent: tropical-year-20260505-0
summary:
=== 18th and 19th century === From the time of Hipparchus and Ptolemy, the year was based on two equinoxes (or two solstices) some years apart, to average out both observational errors and periodic variations (caused by the gravitational pull of the planets, and the small effect of nutation on the equinox). These effects did not begin to be understood until Newton's time. To model short-term variations of the time between equinoxes (and prevent them from confounding efforts to measure long-term variations) requires precise observations and an elaborate theory of the apparent motion of the Sun. The necessary theories and mathematical tools came together in the 18th century due to the work of Pierre-Simon de Laplace, Joseph Louis Lagrange, and other specialists in celestial mechanics. They were able to compute periodic variations and separate them from the gradual mean motion. They could express the mean longitude of the Sun in a polynomial such as: L0 = A0 + A1T + A2T2 days where T is the time in Julian centuries. The derivative of this formula is an expression of the mean angular velocity, and the inverse of this gives an expression for the length of the tropical year as a


id: tropical-year-20260505-2
file: data/en.wikipedia.org/wiki/Tropical_year-2.md
category: reference
title: Tropical year
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tropical_year
date_saved: 2026-05-05T11:13:34.155727+00:00
instance: kb-cron
parent: tropical-year-20260505-0
summary:
== Time scales and calendar == Apparent solar time is the time indicated by a sundial, and is determined by the apparent motion of the Sun caused by the rotation of the Earth around its axis as well as the revolution of the Earth around the Sun. Mean solar time is corrected for the periodic variations in the apparent velocity of the Sun as the Earth revolves in its orbit. The most important such time scale is Universal Time, which is the mean solar time at 0° longitude (the IERS Reference Meridian). Civil time is based on UT (actually UTC), and civil calendars count mean solar days. However, the rotation of the Earth itself is irregular and is slowing down, with respect to more stable time indicators: specifically, the motion of planets and atomic clocks. Ephemeris time (ET) is the independent variable in the equations of motion of the Solar System, in particular, the equations from Newcomb's work, and this ET was in use from 1960 to 1984. These ephemerides were based on observations made in solar time over a period of several centuries, and as a consequence represent the mean solar second over that period. The SI second, defined


id: tropical-year-20260505-3
file: data/en.wikipedia.org/wiki/Tropical_year-3.md
category: reference
title: Tropical year
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tropical_year
date_saved: 2026-05-05T11:13:34.155727+00:00
instance: kb-cron
parent: tropical-year-20260505-0
summary:
=== Different tropical year definitions === If a different starting longitude for the Sun is chosen than 0° (i.e. ♈︎), then the duration for the Sun to return to the same longitude will be different. This is a second-order effect of the circumstance that the speed of the Earth (and conversely the apparent speed of the Sun) varies in its elliptical orbit: faster in the perihelion, slower in the aphelion. The equinox moves with respect to the perihelion (and both move with respect to the fixed sidereal frame). From one equinox passage to the next, or from one solstice passage to the next, the Sun completes not quite a full elliptic orbit. The time saved depends on where it starts in the orbit. If the starting point is close to the perihelion (such as the December solstice), then the speed is higher than average, and the apparent Sun saves little time for not having to cover a full circle: the "tropical year" is comparatively long. If the starting point is near aphelion, then the speed is lower and the time saved for not having to run the same small arc that the equinox has precessed is longer: that tropical year


id: tzolkinex-20260505-0
file: data/en.wikipedia.org/wiki/Tzolkinex-0.md
category: reference
title: Tzolkinex
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Tzolkinex
date_saved: 2026-05-05T11:13:35.358456+00:00
instance: kb-cron
parent: tzolkinex-20260505-0
summary:
The tzolkinex is an eclipse cycle equal to a period of two saros (13,170.636 days) minus one inex (10,571.946 days). As consecutive eclipses in an inex series belongs to the next consecutive saros series, each consecutive tzolkinex belongs to the previous saros series. The tzolkinex is equal to 2598.691 days (about 7 years, 1 month and 12 days). It is related to the tritos in that a period of one tritos plus one tzolkinex is exactly equal to one saros. It is also related to the inex in that a period of one inex plus one tzolkinex is exactly equal to two saros. It corresponds to: 88 synodic months 95.49723 draconic months 7.49723 eclipse years (15 eclipse seasons) 94.31081 anomalistic months. Because of the non-integer number of anomalistic month each eclipse varies in type, i.e. total vs. annular, and greatly varies in length. From remainder of 0.31081, being near 1⁄3, every third tzolkinex comes close to an even number of anomalistic months, but occurs during a different season, and in the opposite hemisphere, thus they may be of the same type (annular vs. total) but otherwise do not have a similar character. == Details == It was first studied by


id: universal-time-20260505-0
file: data/en.wikipedia.org/wiki/Universal_Time-0.md
category: reference
title: Universal Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Universal_Time
date_saved: 2026-05-05T11:13:36.566553+00:00
instance: kb-cron
parent: universal-time-20260505-0
summary:
Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle (ERA, which serves as the replacement for Greenwich Mean Sidereal Time). UT1 is the same everywhere on Earth. UT1 is required to follow the relationship where Tu = (Julian UT1 date − 2451545.0). == History == Prior to the introduction of standard time, each municipality throughout the clock-using world set its official clock, if it had one, according to the local position of the Sun (see solar time). This served adequately until the introduction of rail travel in Britain, which made it possible to travel fast enough over sufficiently long distances as to require continuous re-setting of timepieces as a train progressed in its daily run through several towns. Starting in 1847, Britain established Greenwich Mean Time (GMT), the mean solar time at Greenwich, England, to solve this problem: all clocks in Great Britain were set to this time regardless of local solar noon. Using


id: universal-time-20260505-1
file: data/en.wikipedia.org/wiki/Universal_Time-1.md
category: reference
title: Universal Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Universal_Time
date_saved: 2026-05-05T11:13:36.566553+00:00
instance: kb-cron
parent: universal-time-20260505-0
summary:
The rotation of the Earth and UT are monitored by the International Earth Rotation and Reference Systems Service (IERS). The International Astronomical Union also is involved in setting standards, but the final arbiter of broadcast standards is the International Telecommunication Union, or ITU. The rotation of the Earth is somewhat irregular and also is very gradually slowing due to tidal acceleration. Furthermore, the length of the second was determined from observations of the Moon between 1750 and 1890. All of these factors cause the modern mean solar day, on the average, to be slightly longer than the nominal 86,400 SI seconds, the traditional number of seconds per day. As UT is thus slightly irregular in its rate, astronomers introduced Ephemeris Time, which has since been replaced by Terrestrial Time (TT). Because Universal Time is determined by the Earth's rotation, which drifts away from more precise atomic-frequency standards, an adjustment (called a leap second) to this atomic time is needed since (as of 2019) 'broadcast time' remains broadly synchronised with solar time. Thus, the civil broadcast standard for time and frequency usually follows International Atomic Time closely, but occasionally step (or "leap") in order to prevent them from drifting too far


id: astronomical-year-numbering-20260505-0
file: data/en.wikipedia.org/wiki/Astronomical_year_numbering-0.md
category: reference
title: Astronomical year numbering
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Astronomical_year_numbering
date_saved: 2026-05-05T11:13:37.692854+00:00
instance: kb-cron
parent: astronomical-year-numbering-20260505-0
summary:
Astronomical year numbering is based on AD/CE year numbering, but follows normal decimal integer numbering more strictly. Thus, it has a year 0; the years before that are designated with negative numbers and the years after that are designated with positive numbers. Astronomers use the Julian calendar for years before 1582, including the year 0, and the Gregorian calendar for years after 1582, as exemplified by Jacques Cassini (1740), Simon Newcomb (1898) and Fred Espenak (2007). The prefix AD and the suffixes CE, BC or BCE (Common Era, Before Christ or Before Common Era) are dropped. The year 1 BC/BCE is numbered 0, the year 2 BC is numbered −1, and in general the year n BC/BCE is numbered "−(n − 1)" (a negative number equal to 1 − n). The numbers of AD/CE years are not changed and are written with either no sign or a positive sign; thus in general n AD/CE is simply n or +n. For normal calculation a number zero is often needed, here most notably when calculating the number of years in a period that spans the epoch; the end years need only be subtracted from each other. The system is so named due


id: philosophy-of-space-and-time-20260505-0
file: data/en.wikipedia.org/wiki/Philosophy_of_space_and_time-0.md
category: reference
title: Philosophy of space and time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Philosophy_of_space_and_time
date_saved: 2026-05-05T11:13:39.423280+00:00
instance: kb-cron
parent: philosophy-of-space-and-time-20260505-0
summary:
The philosophy of space and time is a branch of philosophy concerned with ideas about knowledge and understanding within space and time. Such ideas have been central to philosophy from its inception. The philosophy of space and time was both an inspiration for and a central aspect of early analytic philosophy. The subject focuses on a number of basic issues, including whether time and space exist independently of the mind, whether they exist independently of one another, what accounts for time's apparently unidirectional flow, whether times other than the present moment exist, and questions about the nature of identity (particularly the nature of identity over time). == Ancient and medieval views == The earliest recorded philosophy of time was expounded by the ancient Egyptian thinker Ptahhotep (c. 2650–2600 BC), who said: Follow your desire as long as you live, and do not perform more than is ordered, do not lessen the time of the following desire, for the wasting of time is an abomination to the spirit... The Vedas, the earliest texts on Indian philosophy and Hindu philosophy, dating back to the late 2nd millennium BC, describe ancient Hindu cosmology, in which the universe goes through repeated cycles of creation,


id: philosophy-of-space-and-time-20260505-1
file: data/en.wikipedia.org/wiki/Philosophy_of_space_and_time-1.md
category: reference
title: Philosophy of space and time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Philosophy_of_space_and_time
date_saved: 2026-05-05T11:13:39.423280+00:00
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parent: philosophy-of-space-and-time-20260505-0
summary:
=== Leibniz and Newton === The great debate between defining notions of space and time as real objects themselves (absolute), or mere orderings upon actual objects (relational), began between physicists Isaac Newton (via his spokesman, Samuel Clarke) and Gottfried Leibniz in the papers of the Leibniz–Clarke correspondence. Arguing against the absolutist position, Leibniz offers a number of thought experiments with the purpose of showing that there is contradiction in assuming the existence of facts such as absolute location and velocity. These arguments trade heavily on two principles central to his philosophy: the principle of sufficient reason and the identity of indiscernibles. The principle of sufficient reason holds that for every fact, there is a reason that is sufficient to explain what and why it is the way it is and not otherwise. The identity of indiscernibles states that if there is no way of telling two entities apart, then they are one and the same thing. The example Leibniz uses involves two proposed universes situated in absolute space. The only discernible difference between them is that the latter is positioned five feet to the left of the first. The example is only possible if such a thing as absolute space


id: philosophy-of-space-and-time-20260505-2
file: data/en.wikipedia.org/wiki/Philosophy_of_space_and_time-2.md
category: reference
title: Philosophy of space and time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Philosophy_of_space_and_time
date_saved: 2026-05-05T11:13:39.423280+00:00
instance: kb-cron
parent: philosophy-of-space-and-time-20260505-0
summary:
=== Einstein === Albert Einstein proposed that the laws of physics should be based on the principle of relativity. This principle holds that the rules of physics must be the same for all observers, regardless of the frame of reference that is used, and that light propagates at the same speed in all reference frames. This theory was motivated by Maxwell's equations, which show that electromagnetic waves propagate in a vacuum at the speed of light. However, Maxwell's equations give no indication of what this speed is relative to. Prior to Einstein, it was thought that this speed was relative to a fixed medium, called the luminiferous ether. In contrast, the theory of special relativity postulates that light propagates at the speed of light in all inertial frames, and examines the implications of this postulate. All attempts to measure any speed relative to this ether failed, which can be seen as a confirmation of Einstein's postulate that light propagates at the same speed in all reference frames. Special relativity is a formalization of the principle of relativity that does not contain a privileged inertial frame of reference, such as the luminiferous ether or absolute space, from which Einstein inferred that


id: philosophy-of-space-and-time-20260505-3
file: data/en.wikipedia.org/wiki/Philosophy_of_space_and_time-3.md
category: reference
title: Philosophy of space and time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Philosophy_of_space_and_time
date_saved: 2026-05-05T11:13:39.423280+00:00
instance: kb-cron
parent: philosophy-of-space-and-time-20260505-0
summary:
=== Relativity of simultaneity === According to special relativity, different inertial observers will call different sets of events simultaneous from one another and they will both be right relative to their inertial frame of reference. That is, for example, while observer A may say that events E1 and E2 are simultaneous, another observer B, that's moving in uniform motion relative to observer A, will say that the two events are not simultaneous. This phenomena, known as relativity of simultaneity, has been used to support the metaphysical view known as eternalism and as an objection against presentism. Eternalists maintain that all events in the present, past, and future are, in a sense, ontologically, on a par. This is to say that present events have no privileged existence as compared to events in the past and future. Presentists, on the other hand, maintain that events in the present have a privileged existence (some even maintain that past and future events don't exist). The relativity of simultaneity has been used in the dialectic against presentists because it's hard to see which observer's present could be the one with privileged existence if special relativity says that all inertial frames of reference are on a


id: philosophy-of-space-and-time-20260505-4
file: data/en.wikipedia.org/wiki/Philosophy_of_space_and_time-4.md
category: reference
title: Philosophy of space and time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Philosophy_of_space_and_time
date_saved: 2026-05-05T11:13:39.423280+00:00
instance: kb-cron
parent: philosophy-of-space-and-time-20260505-0
summary:
=== Thermodynamics solution === The second major family of solutions to this problem, and by far the one that has generated the most literature, finds the existence of the direction of time as relating to the nature of thermodynamics. The answer from classical thermodynamics states that while our basic physical theory is, in fact, time-reversal symmetric, thermodynamics is not. In particular, the second law of thermodynamics states that the net entropy of a closed system never decreases, and this explains why we often see glass breaking, but not coming back together. But in statistical mechanics things become more complicated. On one hand, statistical mechanics is far superior to classical thermodynamics, in that thermodynamic behavior, such as glass breaking, can be explained by the fundamental laws of physics paired with a statistical postulate. But statistical mechanics, unlike classical thermodynamics, is time-reversal symmetric. The second law of thermodynamics, as it arises in statistical mechanics, merely states that it is overwhelmingly likely that net entropy will increase, but it is not an absolute law. Current thermodynamic solutions to the problem of the direction of time aim to find some further fact, or feature of the laws of nature to account for this discrepancy.


id: philosophy-of-space-and-time-20260505-5
file: data/en.wikipedia.org/wiki/Philosophy_of_space_and_time-5.md
category: reference
title: Philosophy of space and time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Philosophy_of_space_and_time
date_saved: 2026-05-05T11:13:39.423280+00:00
instance: kb-cron
parent: philosophy-of-space-and-time-20260505-0
summary:
The positions on the persistence of objects are somewhat similar. An endurantist holds that for an object to persist through time is for it to exist completely at different times (each instance of existence we can regard as somehow separate from previous and future instances, though still numerically identical with them). A perdurantist on the other hand holds that for a thing to exist through time is for it to exist as a continuous reality, and that when we consider the thing as a whole we must consider an aggregate of all its "temporal parts" or instances of existing. Endurantism is seen as the conventional view and flows out of our pre-philosophical ideas (when I talk to somebody I think I am talking to that person as a complete object, and not just a part of a cross-temporal being), but perdurantists such as David Lewis have attacked this position. They argue that perdurantism is the superior view for its ability to take account of change in objects. On the whole, Presentists are also endurantists and Eternalists are also perdurantists (and vice versa), but this is not a necessary relation and it is possible to claim, for instance, that time's passage


id: a-series-and-b-series-20260505-0
file: data/en.wikipedia.org/wiki/A_series_and_B_series-0.md
category: reference
title: A series and B series
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/A_series_and_B_series
date_saved: 2026-05-05T11:13:40.580369+00:00
instance: kb-cron
parent: a-series-and-b-series-20260505-0
summary:
In metaphysics, the A series and the B series are two different descriptions of the temporal ordering relation among events. The two series differ principally in their use of tense to describe the temporal relation between events and the resulting ontological implications regarding time. John McTaggart introduced these terms in 1908, in an argument for the unreality of time. They are now commonly used by contemporary philosophers of time. == History == Metaphysical debate about temporal orderings reaches back to the ancient Greek philosophers Heraclitus and Parmenides. Parmenides thought that reality is timeless and unchanging. Heraclitus, in contrast, believed that the world is a process of ceaseless change, flux and decay. Reality for Heraclitus is dynamic and ephemeral, in a state of constant flux, as in his famous statement that it is impossible to step twice into the same river (since the river is flowing). == McTaggart's series == McTaggart distinguished the ancient conceptions as a set of relations. According to McTaggart, there are two distinct modes in which all events can be ordered in time. === A series === In the first mode, events are ordered as future, present, and past. Futurity and pastness allow of degrees, while the


id: absolute-space-and-time-20260505-0
file: data/en.wikipedia.org/wiki/Absolute_space_and_time-0.md
category: reference
title: Absolute space and time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Absolute_space_and_time
date_saved: 2026-05-05T11:13:41.731550+00:00
instance: kb-cron
parent: absolute-space-and-time-20260505-0
summary:
Absolute space and time is a concept in physics and philosophy about the properties of the universe. In physics, absolute space and time may be a preferred frame. == Early concept == A version of the concept of absolute space (in the sense of a preferred frame) can be seen in Aristotelian physics. Robert S. Westman writes that a "whiff" of absolute space can be observed in Copernicus's De revolutionibus orbium coelestium, where Copernicus uses the concept of an immobile sphere of stars. == Newton == Originally introduced by Sir Isaac Newton in Philosophiæ Naturalis Principia Mathematica, the concepts of absolute time and space provided a theoretical foundation that facilitated Newtonian mechanics. According to Newton, absolute time and space respectively are independent aspects of objective reality: Absolute, true and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration: relative, apparent and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time ... According to Newton, absolute time exists independently of any perceiver and progresses at a consistent pace throughout


id: absolute-space-and-time-20260505-1
file: data/en.wikipedia.org/wiki/Absolute_space_and_time-1.md
category: reference
title: Absolute space and time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Absolute_space_and_time
date_saved: 2026-05-05T11:13:41.731550+00:00
instance: kb-cron
parent: absolute-space-and-time-20260505-0
summary:
== Mathematical definitions == Space, as understood in Newtonian mechanics, is three-dimensional and Euclidean, with a fixed orientation. It is denoted E3. If some point O in E3 is fixed and defined as an origin, the position of any point P in E3 is uniquely determined by its radius vector r = O P → {\displaystyle \mathbf {r} ={\vec {OP}}} (the origin of this vector coincides with the point O and its end coincides with the point P). The three-dimensional linear vector space R3 is a set of all radius vectors. The space R3 is endowed with a scalar product ⟨ , ⟩. Time is a scalar which is the same in all space E3 and is denoted as t. The ordered set { t } is called a time axis. Motion (also path or trajectory) is a function r : Δ → R3 that maps a point in the interval Δ from the time axis to a position (radius vector) in R3. The above four concepts are the "well-known" objects mentioned by Isaac Newton in his Principia: I do not define time, space, place and motion, as being well known to all. == Special relativity == The concepts of


id: aevum-20260505-0
file: data/en.wikipedia.org/wiki/Aevum-0.md
category: reference
title: Aevum
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Aevum
date_saved: 2026-05-05T11:13:42.925412+00:00
instance: kb-cron
parent: aevum-20260505-0
summary:
In scholastic philosophy, the aevum (also called aeviternity) is the temporal mode of existence experienced by angels and by the saints in heaven. In some ways, it is a state that logically lies between the eternity (timelessness) of God and the temporal experience of material beings. It is sometimes referred to as "improper eternity" or "participated eternity". == Etymology == The word aevum is Latin, originally signifying "age", "aeon", or "everlasting time". It comes from the Greek term "αἰών" meaning eternity in the atemporal sense. Before the 13th century, the term aevum was used synonymously with eternity. The word aeviternity comes from the Medieval Latin neologism aeviternitas. == History == Both Plato and Aristotle recognized two modes of duration: Time and Eternity. Plato said that the soul must be in time while Aristotle said that the soul must be in eternity. The Neoplatonist philosopher Simplicius of Cilicia, said there must be a third mode to describe celestial bodies and souls which are everlasting but still change. In his exegesis of the Book of Genesis, Augustine of Hippo also recognized a mode of duration distinct from time and eternity. In Augustine's view, Heaven and earth, taken to mean formless matter, were


id: arrow-of-time-20260505-0
file: data/en.wikipedia.org/wiki/Arrow_of_time-0.md
category: reference
title: Arrow of time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Arrow_of_time
date_saved: 2026-05-05T11:13:44.126821+00:00
instance: kb-cron
parent: arrow-of-time-20260505-0
summary:
The arrow of time, also called time's arrow, is the concept positing the "one-way direction" or "asymmetry" of time. It was developed in 1927 by the British astrophysicist Arthur Eddington, and is an unsolved general physics question. This direction, according to Eddington, could be determined by studying the organization of atoms, molecules, and bodies, and might be drawn upon a four-dimensional relativistic map of the world ("a solid block of paper"). The arrow of time paradox was originally recognized in the 1800s for gases (and other substances) as a discrepancy between microscopic and macroscopic description of thermodynamics / statistical physics. At the microscopic level physical processes are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or flow) of time. == Overview == The symmetry of time (T-symmetry) can be understood simply as the following: if time were perfectly symmetrical, a video of real events would seem realistic whether played forwards or backwards. Gravity, for example, is a time-reversible force. A ball that is tossed


id: arrow-of-time-20260505-1
file: data/en.wikipedia.org/wiki/Arrow_of_time-1.md
category: reference
title: Arrow of time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Arrow_of_time
date_saved: 2026-05-05T11:13:44.126821+00:00
instance: kb-cron
parent: arrow-of-time-20260505-0
summary:
A related mental arrow arises because one has the sense that one's perception is a continuous movement from the known past to the unknown future. This phenomenon has two aspects: memory (we remember the past but not the future) and volition (we feel we can influence the future but not the past). The two aspects are a consequence of the causal arrow of time: past events (but not future events) are the cause of our present memories, as more and more correlations are formed between the outer world and our brain (see correlations and the arrow of time); and our present volitions and actions are causes of future events. This is because the increase of entropy is thought to be related to increase of both correlations between a system and its surroundings and of the overall complexity, under an appropriate definition; thus all increase together with time. Past and future are also psychologically associated with additional notions. English, along with other languages, tends to associate the past with "behind" and the future with "ahead", with expressions such as "to look forward to welcoming you", "to look back to the good old times", or "to be years ahead". However, this association


id: arrow-of-time-20260505-2
file: data/en.wikipedia.org/wiki/Arrow_of_time-2.md
category: reference
title: Arrow of time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Arrow_of_time
date_saved: 2026-05-05T11:13:44.126821+00:00
instance: kb-cron
parent: arrow-of-time-20260505-0
summary:
=== Radiative arrow of time === Waves, from radio waves to sound waves to those on a pond from throwing a stone, expand outward from their source, even though the wave equations accommodate solutions of convergent waves as well as radiative ones. This arrow has been reversed in carefully worked experiments that created convergent waves, so this arrow probably follows from the thermodynamic arrow in that meeting the conditions to produce a convergent wave requires more order than the conditions for a radiative wave. Put differently, the probability for initial conditions that produce a convergent wave is much lower than the probability for initial conditions that produce a radiative wave. In fact, normally a radiative wave increases entropy, while a convergent wave decreases it, making the latter contradictory to the second law of thermodynamics in usual circumstances. === Causal arrow of time === A cause precedes its effect: the causal event occurs before the event it causes or affects. Birth, for example, follows a successful conception and not vice versa. Thus causality is intimately bound up with time's arrow. An epistemological problem with using causality as an arrow of time is that, as David Hume maintained, the causal relation per


id: arrow-of-time-20260505-3
file: data/en.wikipedia.org/wiki/Arrow_of_time-3.md
category: reference
title: Arrow of time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Arrow_of_time
date_saved: 2026-05-05T11:13:44.126821+00:00
instance: kb-cron
parent: arrow-of-time-20260505-0
summary:
Certain subatomic interactions involving the weak nuclear force violate the conservation of both parity and charge conjugation, but only very rarely. An example is the kaon decay. According to the CPT theorem, this means they should also be time-irreversible, and so establish an arrow of time. Such processes should be responsible for matter creation in the early universe. That the combination of parity and charge conjugation is broken so rarely means that this arrow only "barely" points in one direction, setting it apart from the other arrows whose direction is much more obvious. This arrow had not been linked to any large-scale temporal behaviour until the work of Joan Vaccaro, who showed that T violation could be responsible for conservation laws and dynamics. == See also == A Brief History of Time Anthropic principle Ilya Prigogine Loschmidt's paradox Maxwell's demon Quantum Zeno effect Royal Institution Christmas Lectures 1999 Samayā Time evolution Time flies like an arrow Time reversal signal processing Wheeler–Feynman absorber theory == References == == Further reading == Lebowitz, Joel L. (2008). "Time's arrow and Boltzmann's entropy". Scholarpedia. 3 (4): 3448. Bibcode:2008SchpJ...3.3448L. doi:10.4249/scholarpedia.3448. Boltzmann, Ludwig (1964). Lectures On Gas Theory. University Of California Press. Translated from the original


id: atom-time-20260505-0
file: data/en.wikipedia.org/wiki/Atom_(time)-0.md
category: reference
title: Atom (time)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Atom_(time)
date_saved: 2026-05-05T11:13:45.286592+00:00
instance: kb-cron
parent: atom-time-20260505-0
summary:
An atom of time is the smallest possible unit of time. == History == One of the earliest occurrences of the word "atom" to mean the smallest possible unit of measuring time is found in the Greek text of the New Testament in Paul's 1 Corinthians 15:52. The text compares the length of time of the "atom" to the time needed for "the twinkling of an eye." The text reads: "ἐν ἀτόμῳ, ἐν ῥιπῇ ὀφθαλμοῦ" – "en atomo, en ripe ophthamou" – the word "atom" is usually translated "a moment" – "In a moment, in the twinkling of an eye". It was later referred to in medieval philosophical writings in this sense as the smallest possible division of time. The earliest known occurrence in English is in Byrhtferth's Enchiridion of 1010–1012, where it was defined as 1/564 of a momentum (1½ minutes), and thus equal to almost 160 milliseconds. It was used in the computus, the calculation used to determine the calendar date of Easter. == See also == Planck time == References ==


id: b-theory-of-time-20260505-0
file: data/en.wikipedia.org/wiki/B-theory_of_time-0.md
category: reference
title: B-theory of time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/B-theory_of_time
date_saved: 2026-05-05T11:13:46.457538+00:00
instance: kb-cron
parent: b-theory-of-time-20260505-0
summary:
The B-theory of time, also called the "tenseless theory of time", is one of two positions regarding the temporal ordering of events in the philosophy of time. B-theorists argue that the flow of time is only a subjective illusion of human consciousness, that the past, present, and future are equally real, and that time is tenseless: temporal becoming is not an objective feature of reality. Therefore, there is nothing privileged about the present, ontologically speaking. The B-theory is derived from a distinction drawn by J. M. E. McTaggart between A series and B series. The B-theory is often drawn upon in theoretical physics and is seen in theories such as eternalism. == Origin of terms == The terms A-theory and B-theory, first coined by Richard M. Gale in 1966, derive from Cambridge philosopher J. M. E. McTaggart's analysis of time and change in "The Unreality of Time" (1908), in which events are ordered via a tensed A-series or a tenseless B-series. It is popularly assumed that the A-theory represents time like an A-series, while the B-theory represents time like a B-series. Events (or "times"), McTaggart observed, may be characterized in two distinct but related ways. On the one hand they


id: b-theory-of-time-20260505-1
file: data/en.wikipedia.org/wiki/B-theory_of_time-1.md
category: reference
title: B-theory of time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/B-theory_of_time
date_saved: 2026-05-05T11:13:46.457538+00:00
instance: kb-cron
parent: b-theory-of-time-20260505-0
summary:
=== Irreducibility of tense === Earlier B-theorists argued that one could paraphrase tensed sentences (such as "the sun is now shining", uttered on September 28) into tenseless sentences (such as "on September 28, the sun shines") without loss of meaning. Later B-theorists argued that tenseless sentences could give the truth conditions of tensed sentences or their tokens. Quentin Smith argues that "now" cannot be reduced to descriptions of dates and times, because all date and time descriptions, and therefore truth conditionals, are relative to certain events. Tensed sentences, on the other hand, do not have such truth conditionals. The B-theorist could argue that "now" is reducible to a token-reflexive phrase such as "simultaneous with this utterance", yet Smith states that even such an argument fails to eliminate tense. One can think the statement "I am not uttering anything now", and such a statement would be true. The statement "I am not uttering anything simultaneous with this utterance" is self-contradictory, and cannot be true even when one thinks the statement. Finally, while tensed statements can express token-independent truth values, no token-reflexive statement can do so (by definition of the term "token-reflexive"). Smith claims that proponents of the B-theory argue that the


id: craig-callender-20260505-0
file: data/en.wikipedia.org/wiki/Craig_Callender-0.md
category: reference
title: Craig Callender
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Craig_Callender
date_saved: 2026-05-05T11:13:47.702523+00:00
instance: kb-cron
parent: craig-callender-20260505-0
summary:
Craig Callender (born 1968) is a professor of philosophy at the University of California, San Diego. His main areas of research are philosophy of science, philosophy of physics and metaphysics. == Education and career == Callender obtained his PhD in 1997 from Rutgers University with a thesis entitled Time's Arrow under the supervision of Robert Weingard. From 1996-2000, he worked in the Department of Philosophy, Logic & Scientific Method at the London School of Economics. Currently, he is a professor of philosophy at the University of California, San Diego where he is also the co-director of the Institute for Practical Ethics at the University of California, San Diego. Callender serves on the Committee for Freedom and Responsibility of Science of the International Science Council. Callender has written articles for Scientific American on the philosophy of time and participated in the World Science Festival 2013 with Tim Maudlin and Max Tegmark on the same topic. == Selected publications == In reverse chronological order, unless otherwise specified. === Books === Callender, Craig (2017). What Makes Time Special? Oxford University Press, Oxford, ISBN 978-0-19-879730-2 Callender, Craig, ed. (2011). The Oxford handbook of philosophy of time. Oxford Handbooks in Philosophy. Oxford University Press. ISBN


id: centered-world-20260505-0
file: data/en.wikipedia.org/wiki/Centered_world-0.md
category: reference
title: Centered world
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Centered_world
date_saved: 2026-05-05T11:13:48.889143+00:00
instance: kb-cron
parent: centered-world-20260505-0
summary:
A centered world, according to David Kellogg Lewis, consists of (1) a possible world, (2) an agent in that world, and (3) a time in that world. The concept of centered worlds has epistemic as well as metaphysical uses; for the latter, the three components of a centered world have connections to theories such as actualism, solipsism (especially egocentric presentism and perspectival realism), and presentism, respectively. == References ==


id: chronosophy-20260505-0
file: data/en.wikipedia.org/wiki/Chronosophy-0.md
category: reference
title: Chronosophy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Chronosophy
date_saved: 2026-05-05T11:13:50.070367+00:00
instance: kb-cron
parent: chronosophy-20260505-0
summary:
Chronosophy is the neologistic designation given by scholar Julius Thomas (J.T.) Fraser to "the interdisciplinary and normative study of time sui generis." == Overview == === Etymology === Fraser derived the term from the Ancient Greek: χρόνος, chronos, "time" and σοφία, sophia, "wisdom". Chronosophia is thus defined as the "specific human skill or knowledge . . . pertaining to time . . . [which] all men seem to possess to some degree . . .". === Purpose === Fraser outlined the purpose of the discipline of chronosophy in five intentions, as follows: to encourage the search for new knowledge related to time; to set up and apply criteria regarding which fields of knowledge contribute to an understanding of time, and what they may contribute; to assist in epistemological studies, especially in those related to the structure of knowledge; to provoke communication between the humanities and the sciences using time as the common theme; and to help us learn more about the nature of time by providing channels for the direct confrontation of a multitude of views. === Assumptions === According to Fraser, any pursuit of chronosophical knowledge necessarily makes two assumptions: When specialists speak of 'time', they speak of various


id: chronosophy-20260505-1
file: data/en.wikipedia.org/wiki/Chronosophy-1.md
category: reference
title: Chronosophy
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Chronosophy
date_saved: 2026-05-05T11:13:50.070367+00:00
instance: kb-cron
parent: chronosophy-20260505-0
summary:
expansion beyond or abandonment of [traditional areas of] specialization, and the espousal of interdisciplinary or pan-disciplinary methodologies; (1) is a weak criterion, while (2) is a strong one. Neither of the above criteria make reference to time or temporality; for while the ontological possibly of timeless knowledge must always remain, admission of this possibility begs the question (petitio principii): e.g., what form does timeless knowledge take? how would it come to us? how could we ever be separated from such knowledge to begin with? et cetera ad nauseam. The admission is therefore a paradox (akin to Wittgenstein's seventh proposition in Tractatus Logico-Philosophicus: "Whereof one cannot speak, thereof one must be silent."). We must conclude that the proposal of the possibility of timeless knowledge is both necessary and senseless, a conceptual counterpart to the tautologous nature of the concept of time. Should we come to possess knowledge of that which is "beneath" or "behind" time (or, alternatively, conclude we could never have lost possession of it), there would be no discernible need for further chronosophical inquiry—in the face of such eternal truth, it would instead be chronosophy as currently conceived that would appear both necessary and senseless. Hence: all disciplines are


id: coincidence-20260505-0
file: data/en.wikipedia.org/wiki/Coincidence-0.md
category: reference
title: Coincidence
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Coincidence
date_saved: 2026-05-05T11:13:51.260103+00:00
instance: kb-cron
parent: coincidence-20260505-0
summary:
A coincidence is a remarkable concurrence of events or circumstances that have no apparent causal connection with one another. The perception of remarkable coincidences may lead to supernatural, occult, or paranormal claims, or it may lead to belief in fatalism, which is a doctrine that events will happen in the exact manner of a predetermined plan. In general, the perception of coincidence, for lack of more sophisticated explanations, can serve as a link to folk psychology and philosophy. From a statistical perspective, coincidences are inevitable and often less remarkable than they may appear intuitively. Usually, coincidences are chance events with underestimated probability. An example is the birthday problem, which shows that the probability of two persons having the same birthday already exceeds 50% in a group of only 23 persons. Generalizations of the birthday problem are a key tool used for mathematically modelling coincidences. == Etymology == The first known usage of the word coincidence is from c. 1605 with the meaning "exact correspondence in substance or nature" from the French coincidence, from coincider, from Medieval Latin coincidere. The definition evolved in the 1640s as "occurrence or existence during the same time". The word was introduced to English readers in


id: duration-philosophy-20260505-0
file: data/en.wikipedia.org/wiki/Duration_(philosophy)-0.md
category: reference
title: Duration (philosophy)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Duration_(philosophy)
date_saved: 2026-05-05T11:13:52.453466+00:00
instance: kb-cron
parent: duration-philosophy-20260505-0
summary:
Duration (French: la durée) is a theory of time and consciousness posited by the French philosopher Henri Bergson. Bergson sought to improve upon inadequacies he perceived in the philosophy of Herbert Spencer, due, he believed, to Spencer's lack of comprehension of mechanics, which led Bergson to the conclusion that time eluded mathematics and science. Bergson became aware that the moment one attempted to measure a moment, it would be gone: one measures an immobile, complete line, whereas time is mobile and incomplete. For the individual, time may speed up or slow down, whereas, for science, it would remain the same. Hence Bergson decided to explore the inner life of man, which is a kind of duration, neither a unity nor a quantitative multiplicity. Duration is ineffable and can only be shown indirectly through images that can never reveal a complete picture. It can only be grasped through a simple intuition of the imagination. Bergson first introduced his notion of duration in his essay Time and Free Will: An Essay on the Immediate Data of Consciousness. It is used as a defense of free will in a response to Immanuel Kant, who believed free will was only possible outside time and


id: duration-philosophy-20260505-1
file: data/en.wikipedia.org/wiki/Duration_(philosophy)-1.md
category: reference
title: Duration (philosophy)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Duration_(philosophy)
date_saved: 2026-05-05T11:13:52.453466+00:00
instance: kb-cron
parent: duration-philosophy-20260505-0
summary:
The truth is we change without ceasing...there is no essential difference between passing from one state to another and persisting in the same state. If the state which "remains the same" is more varied than we think, [then] on the other hand the passing of one state to another resembles—more than we imagine—a single state being prolonged: the transition is continuous. Just because we close our eyes to the unceasing variation of every physical state, we are obliged when the change has become so formidable as to force itself on our attention, to speak as if a new state were placed alongside the previous one. Of this new state we assume that it remains unvarying in its turn and so on endlessly. Because a qualitative multiplicity is heterogeneous and yet interpenetrating, it cannot be adequately represented by a symbol; indeed, for Bergson, a qualitative multiplicity is inexpressible. Thus, to grasp duration, one must reverse habitual modes of thought and place oneself within duration by intuition. == Influence on Gilles Deleuze == Gilles Deleuze was profoundly influenced by Bergson's theory of duration, particularly in his work Cinema 1: The Movement Image in which he described cinema as providing people with continuity


id: egocentric-presentism-20260505-0
file: data/en.wikipedia.org/wiki/Egocentric_presentism-0.md
category: reference
title: Egocentric presentism
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Egocentric_presentism
date_saved: 2026-05-05T11:13:53.611819+00:00
instance: kb-cron
parent: egocentric-presentism-20260505-0
summary:
Egocentric presentism is a form of solipsism introduced by Caspar Hare in which other persons can be conscious, but their experiences are simply not present. Similarly, in related work, Hare argues for a theory of perspectival realism in which other perspectives do exist, but the present perspective has a defining intrinsic property. In one example that Hare uses to illustrate his theory (starting on page 354 of the official version of his paper), you learn that you are one of two people, named A and B, who have just been in a train crash; and that A is about to have incredibly painful surgery. You cannot remember your name. According to Hare, naturally, you hope to be B. The point of the example is that you know everything relevant that there is to know about the objective world; all that is missing is your position in it, that is, whose experiences are present, A's or B's. This example is easily handled by egocentric presentism because under this theory, the case where the present experiences are A's is fundamentally different from the case where the present experiences are B's. Hare points out that similar examples can be given to support theories


id: einstein-bergson-debate-20260505-0
file: data/en.wikipedia.org/wiki/Einstein–Bergson_debate-0.md
category: reference
title: Einstein–Bergson debate
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Einstein–Bergson_debate
date_saved: 2026-05-05T11:13:54.954737+00:00
instance: kb-cron
parent: einstein-bergson-debate-20260505-0
summary:
On April 6, 1922, the physicist Albert Einstein and the philosopher Henri Bergson met at the Société française de philosophie and discussed the implications of the theory of relativity on the nature of time. This debate, with the broader discussion it set off, has had wide-ranging implications for Western cosmology and for the prestige of the humanities as compared to science. In 1934, Paul Valéry wrote that the meeting between these two thinkers was the "grande affaire" of the twentieth century. == Context == === Bergson === Henri Bergson was widely viewed as an epoch-defining thinker. For William James, Bergson's Creative Evolution was a work as important for Western philosophy as those of George Berkeley or Immanuel Kant; Jean Wahl concurs, placing Bergson alongside Plato, René Descartes and Kant as one of "the four great philosophers." A cult of personality developed around Bergson following the 1907 publication of Creative Evolution: students would make "mystical pilgrimages" to his summer home in Switzerland; he was referred to as "an enchanter" and "the greatest thinker in the world." His biographer Emily Herring refers to him as being in the early twentieth century "the most famous philosopher in the world." Bergson had a deep


id: einstein-bergson-debate-20260505-1
file: data/en.wikipedia.org/wiki/Einstein–Bergson_debate-1.md
category: reference
title: Einstein–Bergson debate
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Einstein–Bergson_debate
date_saved: 2026-05-05T11:13:54.954737+00:00
instance: kb-cron
parent: einstein-bergson-debate-20260505-0
summary:
Einstein's theory of relativity and his contributions to quantum theory had made him a household name in the scientific community, and by 1919 he even became a public celebrity after the solar eclipse of May 29, 1919, which helped substantiate Einstein's theory of general relativity, with the New York Times proclaiming: “Revolution in Science/New Theory of the Universe/Newtonian Ideas Overthrown.” The new doctrine was widely regarded as necessitating a total overhaul of current understandings of space and time. Einstein's fame had proliferated through his own efforts as well: he had published popular versions of both his treatises, and his Four Lectures on Relativity (delivered in 1921 at Princeton University) had intensified public interest even further. Einstein was invited to France by Paul Langevin, on behalf of the Collège de France, to help “to restore relations between German and French scholars” after World War I, a conflict whose mechanization had enlisted scientists in the service of bloodshed to a previously unprecedented degree. Einstein had opposed the war. On his arrival at the Gare du Nord, Einstein was greeted by crowds of "photographers, reporters, filmmakers, officials and diplomats," and had to slip out a side door to escape the attention. The debate


id: einstein-bergson-debate-20260505-2
file: data/en.wikipedia.org/wiki/Einstein–Bergson_debate-2.md
category: reference
title: Einstein–Bergson debate
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Einstein–Bergson_debate
date_saved: 2026-05-05T11:13:54.954737+00:00
instance: kb-cron
parent: einstein-bergson-debate-20260505-0
summary:
=== Duration and Simultaneity === Later in 1922, Bergson published Duration and Simultaneity, which was explicitly a "confrontation" with Einstein's theory of relativity. It sought to enlist the facts Einstein drew upon in his theories in service of Bergson's vitalist philosophy. He argued that special relativity is rooted in quantifiable clock-time, and that it fails to capture the true essence of time as duration. Distinguishing between "real" time that can be directly experienced and "imaginary" time (i.e. time dilation and relativity of simultaneity) derived form the relativistic formulas, he specifically takes aim at the twin paradox first proposed by Paul Langevin, and calls for the biological aging process to be distinguished from measurable time. In Langevin's example, a traveler makes a round-trip in a rocket for 200 years as measured on Earth, while he himself only experienced 2 years during the flight (see History of the twin paradox). Bergson erroneously rejected this conclusion by claiming that both twins (Peter on Earth and Paul in the rocket) are interchangeable and therefore must be of same age at reunion: p.74: We must now repeat for Paul everything we said about Peter: Since motion is reciprocal, the two people are interchangeable. If, earlier,


id: eternal-return-20260505-0
file: data/en.wikipedia.org/wiki/Eternal_return-0.md
category: reference
title: Eternal return
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Eternal_return
date_saved: 2026-05-05T11:13:56.229279+00:00
instance: kb-cron
parent: eternal-return-20260505-0
summary:
Eternal return (or eternal recurrence) is a philosophical concept which states that time repeats itself in an infinite loop, and that exactly the same events will continue to occur in exactly the same way, over and over again, for eternity. In ancient Greece, the concept of eternal return was most prominently associated with Empedocles and with Stoicism, the school of philosophy founded by Zeno of Citium. The Stoics believed that the universe is periodically destroyed and reborn, and that each universe is exactly the same as the one before. This doctrine was fiercely criticised by Christian authors such as Augustine, who saw in it a fundamental denial of free will and of the possibility of salvation. The spread of Christianity therefore diminished classical theories of eternal return. The concept was revived in the 19th century by German philosopher Friedrich Nietzsche. Having briefly presented the idea as a thought experiment in The Gay Science, he explored it more thoroughly in his novel Thus Spoke Zarathustra, in which the protagonist learns to overcome his horror of the thought of eternal return. It is not known whether Nietzsche believed in the literal truth of eternal return, or, if he did not, what he


id: eternal-return-20260505-1
file: data/en.wikipedia.org/wiki/Eternal_return-1.md
category: reference
title: Eternal return
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Eternal_return
date_saved: 2026-05-05T11:13:56.229279+00:00
instance: kb-cron
parent: eternal-return-20260505-0
summary:
=== Christian response === Christian authors attacked the doctrine of eternal recurrence on various grounds. Origen argued that the theory was incompatible with free will (although he did allow the possibility of diverse and non-identical cycles). Augustine of Hippo (354–430 AD) objected to the fact that salvation was not possible in the Stoic scheme, arguing that even if a temporary happiness was attained, a soul could not be truly blessed if it was doomed to return again to misery. Augustine also mentions "certain philosophers" who cite Ecclesiastes 1:9–10 as evidence of eternal return: "What is that which hath been? It is that which shall be. And what is that which is done? It is that which shall be done: and there is no new thing under the sun. Who can speak and say, See, this is new? It hath been already of old time, which was before us." Augustine denies that this has reference to the recurrence of specific people, objects, and events, instead interpreting the passage in a more general sense. In support of his argument, he appeals to scriptural passages such as Romans 6:9, which affirms that Christ "being raised from the dead dieth no more". == Friedrich


id: eternal-return-20260505-2
file: data/en.wikipedia.org/wiki/Eternal_return-2.md
category: reference
title: Eternal return
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Eternal_return
date_saved: 2026-05-05T11:13:56.229279+00:00
instance: kb-cron
parent: eternal-return-20260505-0
summary:
=== Interpretation === Martin Heidegger points out that Nietzsche's first mention of eternal recurrence in The Gay Science presents this concept as a hypothetical question rather than postulating it as a fact. Many readings argue that Nietzsche was not attempting to make a cosmological or theoretical claim i.e. saying that eternal recurrence is a true statement about how the world works. Instead, the emotional reaction to the thought experiment serves to reveal whether one is living life to the best. According to Heidegger, the significant point is the burden imposed by the question of eternal recurrence, regardless of whether or not such a thing could possibly be true. The idea is similar to Nietzsche's concept of amor fati, which he describes in Ecce Homo: "My formula for greatness in a human being is amor fati: that one wants nothing to be different, not forward, not backward, not in all eternity. Not merely to bear what is necessary, still less conceal it ... but love it." On the other hand, Nietzsche's posthumously published notebooks contain an attempt at a logical proof of eternal return, which is often adduced in support of the claim that Nietzsche believed in the theory as a


id: eternalism-philosophy-of-time-20260505-0
file: data/en.wikipedia.org/wiki/Eternalism_(philosophy_of_time)-0.md
category: reference
title: Eternalism (philosophy of time)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time)
date_saved: 2026-05-05T11:13:57.502214+00:00
instance: kb-cron
parent: eternalism-philosophy-of-time-20260505-0
summary:
In the philosophy of space and time, eternalism is an ontological view according to which all existence in time is equally real, as opposed to presentism or the growing block universe theory of time, in which at least the future is not the same as any other time. Some forms of eternalism give time a similar ontology to that of space, as a dimension, with different times being as real as different places, and future events are "already there" in the same sense other places are already there, and that there is no objective flow of time. It is sometimes referred to as the "block time" or "block universe" theory due to its description of space-time as an unchanging four-dimensional "block", as opposed to the view of the world as a three-dimensional space modulated by the passage of time. == The present == In classical philosophy, time is divided into three distinct regions: the "past", the "present", and the "future". Using that representational model, the past is generally seen as being immutably fixed, and the future as at least partly undefined. As time passes, the moment that was once the present becomes part of the past, and part of the


id: eternalism-philosophy-of-time-20260505-1
file: data/en.wikipedia.org/wiki/Eternalism_(philosophy_of_time)-1.md
category: reference
title: Eternalism (philosophy of time)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Eternalism_(philosophy_of_time)
date_saved: 2026-05-05T11:13:57.502214+00:00
instance: kb-cron
parent: eternalism-philosophy-of-time-20260505-0
summary:
=== Modern period === One of the most famous arguments about the nature of time in modern philosophy is presented in The Unreality of Time by J. M. E. McTaggart. It argues that time is an illusion. McTaggart argued that the description of events as existing in absolute time is self-contradictory, because the events have to have properties about being in the past and in the future, which are incompatible with each other. McTaggart viewed this as a contradiction in the concept of time itself, and concluded that reality is non-temporal. He called this concept the B-theory of time. Dirck Vorenkamp, a professor of religious studies, argued in his paper "B-Series Temporal Order in Dogen's Theory of Time" that the Zen Buddhist teacher Dōgen presented views on time that contained all the main elements of McTaggart's B-series view of time (which denies any objective present), although he noted that some of Dōgen's reasoning also contained A-Series notions, which Vorenkamp argued may indicate some inconsistency in Dōgen's thinking. Eternalism also encapsulates the theory of world lines, and the concept of linear reality that is - the individual perception of linear time. === Quantum physics === Some philosophers appeal to a specific


id: eternity-20260505-0
file: data/en.wikipedia.org/wiki/Eternity-0.md
category: reference
title: Eternity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Eternity
date_saved: 2026-05-05T11:13:58.699406+00:00
instance: kb-cron
parent: eternity-20260505-0
summary:
Eternity, also referred to as sempiternity or forever, is time with no end i.e. infinite. In the context of human life, eternity and death are co-existing realities. == Etymology == Cicero used the word aeternitatis, written at some uncertain time between the years 88 - 81 BC (work: De Inventione 1, 27, 39. : tempus autem est—id quo nunc utimur, nam ipsum quidem generaliter definire difficile est—pars quaedam aeternitatis cum alicuius annui, menstrui, diurni nocturnive spatii certa significatione.) which is an early or the earliest extant written form from which the English word is derived; first shown in history in an approx. 1374 translation by Chaucer. The first usage in French is 1175: eternitez: B. de Ste-Maure, 'Ducs Normandie. == Philosophy == Classical period (8th-7th century BC - 5th-9th century AD) Plato (c. 428–423 BC - 348/347 BC) described time as the moving image of eternity in Timaeus (37 D) using the word: αἰών. Aristotle (384–322 BC) stated οὐρανοῦ was eternal (in Book I of Περὶ οὐρανοῦ) and an eternal world (in Physics). The ancient Greek word for everlastingness was ἀίδιος (aidios) as exists via Plotinus, who also used the word aoin (eternity), in Ennead III.7. The thought of Classical


id: eternity-of-the-world-20260505-0
file: data/en.wikipedia.org/wiki/Eternity_of_the_world-0.md
category: reference
title: Eternity of the world
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Eternity_of_the_world
date_saved: 2026-05-05T11:13:59.985243+00:00
instance: kb-cron
parent: eternity-of-the-world-20260505-0
summary:
The eternity of the world is the question, in philosophy, of whether the world has a beginning in time or has existed for eternity. It was a concern for ancient philosophers as well as theologians and philosophers of the 13th century. The problem became a focus of a dispute in the 13th century, when some of the works of Aristotle, who believed in the eternity of the world, were rediscovered in the Latin West. This view conflicted with the view of the Catholic Church that the world had a beginning in time. The Aristotelian view was prohibited in the Condemnations of 1210–1277. == Aristotle == The ancient Greek philosopher Aristotle argued that the world must have existed from eternity in his Physics as follows. In Book I, he argues that everything that comes into existence does so from a substratum. Therefore, if the underlying matter of the universe came into existence, it would come into existence from a substratum. But the nature of matter is precisely to be the substratum from which other things arise. Consequently, the underlying matter of the universe could have come into existence only from an already existing matter exactly like itself; to assume that the


id: eternity-of-the-world-20260505-1
file: data/en.wikipedia.org/wiki/Eternity_of_the_world-1.md
category: reference
title: Eternity of the world
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Eternity_of_the_world
date_saved: 2026-05-05T11:13:59.985243+00:00
instance: kb-cron
parent: eternity-of-the-world-20260505-0
summary:
"An actual infinite cannot exist." "An infinite temporal regress of events is an actual infinite." "Thus an infinite temporal regress of events cannot exist." This argument defines event as equal increments of time. Philoponus argues that the second premise is not controversial since the number of events prior to today would be an actual infinite without beginning if the universe is eternal. The first premise is defended by a reductio ad absurdum where Philoponus shows that actual infinites can not exist in the actual world because they would lead to contradictions albeit being a possible mathematical enterprise. Since an actual infinite in reality would create logical contradictions, it can not exist including the actual infinite set of past events. The second argument, the "argument from the impossibility of completing an actual infinite by successive addition", states: "An actual infinite cannot be completed by successive addition." "The temporal series of past events has been completed by successive addition." "Thus the temporal series of past events cannot be an actual infinite." The first statement states, correctly, that a finite (number) cannot be made into an infinite one by the finite addition of more finite numbers. The second skirts around this; the analogous


id: event-philosophy-20260505-0
file: data/en.wikipedia.org/wiki/Event_(philosophy)-0.md
category: reference
title: Event (philosophy)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Event_(philosophy)
date_saved: 2026-05-05T11:14:01.214153+00:00
instance: kb-cron
parent: event-philosophy-20260505-0
summary:
In philosophy, events are objects in time or instantiations of properties in objects. On some views, only changes in the form of acquiring or losing a property can constitute events, like the lawn's becoming dry. According to others, there are also events that involve nothing but the retaining of a property, e.g. the lawn's staying wet. Events are usually defined as particulars that, unlike universals, cannot repeat at different times. Processes are complex events constituted by a sequence of events. But even simple events can be conceived as complex entities involving an object, a time and the property exemplified by the object at this time. Traditionally, metaphysicians tended to emphasize static being over dynamic events. This tendency has been opposed by so-called process philosophy or process ontology, which ascribes ontological primacy to events and processes. == Kim’s property-exemplification == Jaegwon Kim theorized that events are structured. They are composed of three things: object(s) [ x ] {\displaystyle [x]} , a property [ P ] {\displaystyle [P]} and time or a temporal interval [ t ] {\displaystyle [t]} . Events are defined using the operation [ x , P , t ] {\displaystyle [x,P,t]} . A unique event is defined by


id: event-philosophy-20260505-1
file: data/en.wikipedia.org/wiki/Event_(philosophy)-1.md
category: reference
title: Event (philosophy)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Event_(philosophy)
date_saved: 2026-05-05T11:14:01.214153+00:00
instance: kb-cron
parent: event-philosophy-20260505-0
summary:
== Lewis == David Lewis theorized that events are merely spatiotemporal regions and properties (i.e. membership of a class). He defines an event as "e is an event only if it is a class of spatiotemporal regions, both thisworldly (assuming it occurs in the actual world) and otherworldly." The only problem with this definition is it only tells us what an event could be, but does not define a unique event. This theory entails modal realism, which assumes possible worlds exist; worlds are defined as sets containing all objects that exist as a part of that set. However, this theory is controversial. Some philosophers have attempted to remove possible worlds, and reduce them to other entities. They hold that the world we exist in is the only world that actually exists, and that possible worlds are only possibilities. Lewis’ theory is composed of four key points. Firstly, the non-duplication principle; it states that x and y are separate events if and only if there is one member of x that is not a member of y (or vice versa). Secondly, there exist regions that are subsets of possible worlds and thirdly, events are not structured by an essential time. ==


id: an-experiment-with-time-20260505-0
file: data/en.wikipedia.org/wiki/An_Experiment_with_Time-0.md
category: reference
title: An Experiment with Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/An_Experiment_with_Time
date_saved: 2026-05-05T11:14:02.376353+00:00
instance: kb-cron
parent: an-experiment-with-time-20260505-0
summary:
An Experiment with Time is a book by the British soldier, aeronautical engineer and philosopher J. W. Dunne (1875–1949) about his precognitive dreams and a theory of time which he later called "Serialism". First published in March 1927, the book was widely read. Although never accepted by mainstream scientists or philosophers, it has influenced imaginative literature ever since. Dunne published four sequels: The Serial Universe (1934), The New Immortality (1938), Nothing Dies (1940) and Intrusions? (1955). == Description == === Overview === An Experiment with Time discusses two main topics. The first half of the book describes a number of precognitive dreams, most of which Dunne himself had experienced. His key conclusion was that such precognitive visions foresee future personal experiences by the dreamer and not mere general events. The second half develops a theory to try to explain them. Dunne's starting point is the observation that the moment of "now" is not described by science. Contemporary science described physical time as a fourth dimension and Dunne's argument led to an endless sequence of higher dimensions of time to measure our passage through the dimension below. Accompanying each level was a higher level of consciousness. At the end of the


id: an-experiment-with-time-20260505-1
file: data/en.wikipedia.org/wiki/An_Experiment_with_Time-1.md
category: reference
title: An Experiment with Time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/An_Experiment_with_Time
date_saved: 2026-05-05T11:14:02.376353+00:00
instance: kb-cron
parent: an-experiment-with-time-20260505-0
summary:
== Publishing history == An Experiment with Time was first published by A & C Black in March 1927. Dunne continued to update it and many new editions and impressions were published over his lifetime. Black brought out a 1929 second edition, prefaced with editorial notes and an extract from a 1928 letter from Arthur Eddington. Dunne then changed publisher to Faber & Faber, with whom he would remain. The third edition incorporated major new material and was published by Faber's in 1932; this and subsequent editions were published in the US by Macmillan. The final version which he had a hand in was published as a "reprint" in 1948. Faber continued printing paperback editions until at least 1973, and others have appeared since. == Reception == === Academic === Initial reactions from the scientific and scientifically-minded community were broadly positive. Nature carried a review by the philosopher and mathematician Hyman Levy. They accepted that Dunne was a sober and rational investigator who was doing his best to take a scientific approach. They acknowledged that if his ideas about time and consciousness were true then his book would be truly revolutionary. However opinions differed over the existence of dream precognition,


id: from-eternity-to-here-20260505-0
file: data/en.wikipedia.org/wiki/From_Eternity_to_Here-0.md
category: reference
title: From Eternity to Here
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/From_Eternity_to_Here
date_saved: 2026-05-05T11:14:03.535877+00:00
instance: kb-cron
parent: from-eternity-to-here-20260505-0
summary:
From Eternity to Here: The Quest for the Ultimate Theory of Time is a nonfiction book by American theoretical physicist Sean M. Carroll, published on January 7, 2010, by Dutton. == Background == In the book, Carroll explores the nature of the arrow of time, that goes forward from the past to the future, and posits that the arrow owes its existence to conditions before the Big Bang. However, reasoning about what was there before the Big Bang has traditionally been dismissed as meaningless, for space and time are considered to be created exactly at the Big Bang. Carroll argues that "understanding the arrow of time is a matter of understanding the origin of the universe" and in his explanations relies on the second law of thermodynamics, which states that all systems in the Universe tend to become more and more disorganized (increase in entropy). His proposed explanation for the arrow of time is based on ideas that go back to Ludwig Boltzmann, an Austrian physicist of the 1870s. == Book organization == The book is divided into four parts and 15 chapters and has an appendix for the relevant math. Part one is entitled, "Time, Experience, and the Universe."


id: further-facts-20260505-0
file: data/en.wikipedia.org/wiki/Further_facts-0.md
category: reference
title: Further facts
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Further_facts
date_saved: 2026-05-05T11:14:04.749751+00:00
instance: kb-cron
parent: further-facts-20260505-0
summary:
In philosophy, further facts are facts that do not logically follow from the physical facts of the world. Reductionists who argue that at bottom there is nothing more than the physical facts thus argue against the existence of further facts. The concept of further facts plays a key role in some of the major works in analytic philosophy of the late 20th century, including in Derek Parfit's Reasons and Persons, and David Chalmers's The Conscious Mind. One context in which the existence of further facts is debated is that of personal identity across time: in what sense is Alice today the same person as Alice yesterday, given that across the two days the state of her brain is different and the atoms that constitute her are different? On the one hand, we may believe that at bottom, there is nothing more than the atoms and their arrangement at different points in time; while we may for practical purposes come up with some notion of sameness of a person, this notion does not reflect anything deeper about reality. Under such a view there would be no further facts. On the other hand, we may believe that there is an additional fact


id: future-20260505-0
file: data/en.wikipedia.org/wiki/Future-0.md
category: reference
title: Future
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Future
date_saved: 2026-05-05T11:14:05.922691+00:00
instance: kb-cron
parent: future-20260505-0
summary:
The future is the time after the past and the present. Its arrival is considered inevitable due to the existence of time and the laws of physics. Due to the apparent nature of the reality and the unavoidability of the future, everything that currently exists and will exist can be categorized as either permanent, meaning that it will exist forever, or temporary, meaning that it will end. In the Occidental view, which uses a linear conception of time, the future is the portion of the projected timeline that is anticipated to occur. In special relativity, the future is considered absolute future, or the future light cone. In the philosophy of time, presentism is the belief that only the present exists and the future and the past are unreal. Religions consider the future when they address issues such as karma, life after death, and eschatologies that study what the end of time and the end of the world will be. Religious figures such as prophets and diviners have claimed to see into the future. Future studies, or futurology, is the science, art, and practice of postulating possible futures. Modern practitioners stress the importance of alternative and plural futures, rather than one


id: future-20260505-1
file: data/en.wikipedia.org/wiki/Future-1.md
category: reference
title: Future
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Future
date_saved: 2026-05-05T11:14:05.922691+00:00
instance: kb-cron
parent: future-20260505-0
summary:
== In psychology == Human behavior is known to encompass anticipation of the future. Anticipatory behavior can be the result of a psychological outlook toward the future, for examples optimism, pessimism, and hope. Optimism is an outlook on life such that one maintains a view of the world as a positive place. People would say that optimism is seeing the glass "half full" of water as opposed to half empty. It is the philosophical opposite of pessimism. Optimists generally believe that people and events are inherently good, so that most situations work out in the end for the best. Hope is a belief in a positive outcome related to events and circumstances in one's life. Hope implies a certain amount of despair, wanting, wishing, suffering or perseverance—i.e., believing that a better or positive outcome is possible even when there is some evidence to the contrary. "Hopefulness" is somewhat different from optimism in that hope is an emotional state, whereas some theories point to optimism as a conclusion reached through a deliberate thought pattern that leads to a positive personal attitudes and by extension is linked to more philanthropic behaviours. Pessimism as stated before is the opposite of optimism. It is


id: future-20260505-2
file: data/en.wikipedia.org/wiki/Future-2.md
category: reference
title: Future
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Future
date_saved: 2026-05-05T11:14:05.922691+00:00
instance: kb-cron
parent: future-20260505-0
summary:
In English grammar, actions are classified according to one of the following twelve verb tenses: past (past, past continuous, past perfect, or past perfect continuous), present (present, present continuous, present perfect, or present perfect continuous), or future (future, future continuous, future perfect, or future perfect continuous). The future tense refers to actions that have not yet happened, but which are due, expected, or may occur in the future. For example, in the sentence, "She will walk home," the verb "will walk" is in the future tense because it refers to an action that is going to, or may, happen at a point in time beyond the present. Verbs in the future continuous tense indicate actions that will happen beyond the present and will continue for a period of time. In the sentence, "She will be walking home," the verb phrase "will be walking" is in the future continuous tense because the action described is not happening now, but will happen sometime afterwards and is expected to continue happening for some time. Verbs in the future perfect tense indicate actions that will be completed at a particular point in the future. For example, the verb phrase, "will have walked," in the


id: future-20260505-3
file: data/en.wikipedia.org/wiki/Future-3.md
category: reference
title: Future
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Future
date_saved: 2026-05-05T11:14:05.922691+00:00
instance: kb-cron
parent: future-20260505-0
summary:
Forecasting is the process of estimating outcomes in uncontrolled situations. Forecasting is applied in many areas, such as weather forecasting, earthquake prediction, transport planning, and labour market planning. Due to the element of the unknown, risk and uncertainty are central to forecasting. Statistically based forecasting employs time series with cross-sectional or longitudinal data. Econometric forecasting methods use the assumption that it is possible to identify the underlying factors that might influence the variable that is being forecast. If the causes are understood, projections of the influencing variables can be made and used in the forecast. Judgmental forecasting methods incorporate intuitive judgments, opinions, and probability estimates, as in the case of the Delphi method, scenario building, and simulations. Prediction is similar to forecasting but is used more generally, for instance, to also include baseless claims on the future. Organized efforts to predict the future began with practices like astrology, haruspicy, and augury. These are all considered to be pseudoscience today, evolving from the human desire to know the future in advance. Modern efforts such as futures studies attempt to predict technological and societal trends, while more ancient practices, such as weather forecasting, have benefited from scientific and causal modelling. Despite the


id: grim-reaper-paradox-20260505-0
file: data/en.wikipedia.org/wiki/Grim_Reaper_paradox-0.md
category: reference
title: Grim Reaper paradox
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Grim_Reaper_paradox
date_saved: 2026-05-05T11:14:07.081424+00:00
instance: kb-cron
parent: grim-reaper-paradox-20260505-0
summary:
In philosophy, the Grim Reaper paradox is a paradox involving an infinite sequence of Grim Reapers, each tasked with killing a person if no reaper has already killed them. The paradox raises questions about the possibility of continuous time and the infinite past (temporal finitism). It is inspired by J. A. Benardete's paradoxes from the 1964 book Infinity: An Essay in Metaphysics. Various formulations of paradoxes involving beginningless sets, whose members perform a function only if no previous member performs it, are all labelled "Benardete Paradoxes". These are examples of supertasks. == Paradox == The paradox supposes there is an infinite sequence of Reapers, each assigned a time to kill a particular person. Each Reaper will only kill this person if no earlier Reaper has already killed them. It is 12pm, and the first Reaper is set to kill the person at 1pm. The second Reaper is set to kill them at 12:30pm, the third at 12:15pm, and so on. As a consequence of these propositions, the person will certainly be killed by a Reaper before 1pm; however, no individual Reaper can kill them, as there is always an earlier Reaper who would do so first. Therefore, it is impossible


id: growing-block-universe-20260505-0
file: data/en.wikipedia.org/wiki/Growing_block_universe-0.md
category: reference
title: Growing block universe
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Growing_block_universe
date_saved: 2026-05-05T11:14:08.271158+00:00
instance: kb-cron
parent: growing-block-universe-20260505-0
summary:
The growing block universe, or the growing block view, is a theory of time arguing that the past and present both exist, while the future does not yet exist. The present is the perpetuating factor of time, where new moments are added to the past. By the passage of time more of the world comes into being; therefore, the block universe is said to be growing. The growth of the block is supposed to happen in the present, a very thin slice of spacetime, where more of spacetime is continually coming into being. Growing block theory should not be confused with block universe theory, also known as eternalism. The growing block view is an alternative to both eternalism (according to which past, present, and future all exist) and presentism (according to which only the present exists). It is held to be closer to common-sense intuitions than the alternatives. C. D. Broad was a proponent of the theory (1923). Some modern defenders are Michael Tooley (in 1997) and Peter Forrest (in 2004). Fabrice Correia and Sven Rosenkranz (2015) have developed their own distinctive view of this theory. == Overview == Broad first proposed the theory in 1923. He described the theory


id: hauntology-20260505-0
file: data/en.wikipedia.org/wiki/Hauntology-0.md
category: reference
title: Hauntology
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hauntology
date_saved: 2026-05-05T11:14:10.113007+00:00
instance: kb-cron
parent: hauntology-20260505-0
summary:
Hauntology (a portmanteau of haunting and ontology, also spectral studies, spectralities, or the spectral turn) is a range of ideas referring to the return or persistence of elements from the social or cultural past, as if to haunt the present. The term is a neologism first introduced by French philosopher Jacques Derrida in his 1993 book Spectres of Marx. It has since been invoked in fields such as visual arts, philosophy, electronic music, anthropology, criminology, politics, fiction, and literary criticism. While Christine Brooke-Rose had previously punned "dehauntological" (on "deontological") in Amalgamemnon (1984), Derrida initially used "hauntology" for his idea of the atemporal nature of Marxism and its tendency to "haunt Western society from beyond the grave". It describes a situation of temporal and ontological disjunction in which presence, especially socially and culturally, is replaced by a deferred non-origin. The concept is derived from deconstruction, in which any attempt to locate the origin of identity or history must inevitably find itself dependent on an always-already existing set of linguistic conditions. Despite being the central focus of Spectres of Marx, the word hauntology appears only three times in the book, and there is little consistency in how other writers define the term.


id: hauntology-20260505-1
file: data/en.wikipedia.org/wiki/Hauntology-1.md
category: reference
title: Hauntology
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Hauntology
date_saved: 2026-05-05T11:14:10.113007+00:00
instance: kb-cron
parent: hauntology-20260505-0
summary:
Anthropologists Martha and Bruce Lincoln make a distinction between primary hauntings, in which the haunted recognize the reality and autonomy of metaphysical entities in relatively uncritical, literal manner; and secondary hauntings, which identify "textual residues" history, or as tropes for "collective intrapsychic states" such as trauma and grief. As a case study, they use the example of Ba Chúc's secondary haunting, in which the state-controlled museums display the skulls of the dead and memorabilia, as opposed to traditional Vietnamese burial customs. This is contrasted with the "primary haunting" of Ba Chúc, the paranormal activity said to occur at an execution site marked by a tree. Kit Bauserman notes that for literary and critical theorists, the ghost is "pure metaphor" and "a fictional vessel that co-opts their social agenda", whereas ethnographers and anthropologists "come the closest to engaging ghosts as beings". Some scholars have argued that the "neat distinction quickly breaks down in ethnographic analysis" and that "it is far from clear that the presence of ghosts as metaphysical entities is primary." == See also == Cultural memory Eternal return National memory == Notes == == References == Blanco, María del Pilar; Peeren, Esther (2013). The spectralities reader : ghosts and


id: if-you-find-this-world-bad-you-should-see-some-of-the-others-20260505-0
file: data/en.wikipedia.org/wiki/If_You_Find_This_World_Bad,_You_Should_See_Some_of_the_Others-0.md
category: reference
title: If You Find This World Bad, You Should See Some of the Others
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/If_You_Find_This_World_Bad,_You_Should_See_Some_of_the_Others
date_saved: 2026-05-05T11:14:11.807272+00:00
instance: kb-cron
parent: if-you-find-this-world-bad-you-should-see-some-of-the-others-20260505-0
summary:
"If You Find This World Bad, You Should See Some of the Others", also known as the "Metz speech", is a 1977 speech and essay by science fiction writer Philip K. Dick. He delivered it as the guest of honor on September 24, 1977, at the Second Metz International Science Fiction Festival in Metz, France. Dick prepared his first version of the speech by May of that year, but was asked to deliver a shorter version due to time constraints. The Metz speech, in its shorter form, was recorded on video and was translated to the French audience by an interpreter. Dick's speech lays out his characteristic, yet arcane thoughts on the philosophy of space and time and the concept of alternate universes within a hypothetical multiverse. The speech also discusses Dick's strange and unusual visions from 1974, his interpretation of Christian Gnosticism, and the role of alternate history in his published work. The speech was not well received. Dick spoke in a monotone voice, the interpreter's transcript differed from Dick's speech due to a last minute rewrite, and the audience was left confused and bewildered. At the time, nobody knew exactly what to make of the speech, as it


id: if-you-find-this-world-bad-you-should-see-some-of-the-others-20260505-1
file: data/en.wikipedia.org/wiki/If_You_Find_This_World_Bad,_You_Should_See_Some_of_the_Others-1.md
category: reference
title: If You Find This World Bad, You Should See Some of the Others
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/If_You_Find_This_World_Bad,_You_Should_See_Some_of_the_Others
date_saved: 2026-05-05T11:14:11.807272+00:00
instance: kb-cron
parent: if-you-find-this-world-bad-you-should-see-some-of-the-others-20260505-0
summary:
== Invitation and preparation == The first Metz International Science Fiction Festival (Festival International de la Science-Fiction de Metz) took place from May 24–30, 1976, founded by Philippe Hupp, a book reviewer and French translator of Time out of Joint (1959), as well as a columnist for the French version of Galaxy Science Fiction. Building on the momentum from the success of the first festival, Hupp invited Dick on February 23, 1977, to attend the second festival as the guest of honor. Dick accepted on March 17, and responded to Hupp with a brief description of his planned speech. Even though Dick had accepted the invitation, his reputation for not showing up to conferences was well known. Hupp flew to the United States to make the case to Dick in person. They met for lunch at an Italian restaurant near his apartment in Santa Ana, California. Hupp sold him on the festival, explaining exactly how it would work and how Dick would be taken care of during his time in France. At the meeting, Dick gave Hupp an audio cassette of the speech he had already prepared (dated May 21), and they enjoyed a meal over two bottles of red


id: if-you-find-this-world-bad-you-should-see-some-of-the-others-20260505-2
file: data/en.wikipedia.org/wiki/If_You_Find_This_World_Bad,_You_Should_See_Some_of_the_Others-2.md
category: reference
title: If You Find This World Bad, You Should See Some of the Others
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/If_You_Find_This_World_Bad,_You_Should_See_Some_of_the_Others
date_saved: 2026-05-05T11:14:11.807272+00:00
instance: kb-cron
parent: if-you-find-this-world-bad-you-should-see-some-of-the-others-20260505-0
summary:
== Synopsis == Dick proposes that novelists have a lot of ideas to work with, but most of these are meaningless and of no value. And yet, try as they might, over their entire career, a novelist may only come across a few great ideas. Dick argues that the novelist does not find or create these ideas on their own, rather these ideas are like living entities that seek out the novelist to make themselves manifest to the larger world, to history itself. To support this argument, Dick cites the pre-Socratic philosophers, who proposed the cosmos was a thinking entity, as well as theistic ideas found in works related to Indian Vedanta, Spinoza, and Alfred North Whitehead. Dick points to the existence of a hidden, gnostic, God-like figure, citing the Sufi poet Rumi to make his point: "The workman is invisible within the workshop". From this, Dick places these ideas within a continuum of multiple, parallel universes in a lateral axis of time, independent of linear progression, which he admits is absurd and nonsensical, and undermines his own belief in pantheistic monism. More importantly, Dick asks, what kind of changes would people experience if these realities were to be altered?


id: if-you-find-this-world-bad-you-should-see-some-of-the-others-20260505-3
file: data/en.wikipedia.org/wiki/If_You_Find_This_World_Bad,_You_Should_See_Some_of_the_Others-3.md
category: reference
title: If You Find This World Bad, You Should See Some of the Others
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/If_You_Find_This_World_Bad,_You_Should_See_Some_of_the_Others
date_saved: 2026-05-05T11:14:11.807272+00:00
instance: kb-cron
parent: if-you-find-this-world-bad-you-should-see-some-of-the-others-20260505-0
summary:
== Critical reception == Harlan Ellison did not attend Dick's speech, as they had been estranged since 1975 at the time. Ellison recalled that the people who heard the speech "looked like they had been stunned by a ball peen hammer...they thought [Dick] was either drunk or doped". John Brunner, who originally met Dick in 1964 at a party before Worldcon in Oakland, recalled his own confusion on the matter a decade later: "I...failed to figure out how literally [Dick] intended people to regard his claims", wrote Brunner. "I could not decide whether, after so many years of inner suffering, his reason had been usurped by his own inventions, or whether he had reached the bitter conclusion that the only way to cope with our lunatic world was to treat it as one vast and rather vicious joke, and fight back on the same irrational level." Dick's friend Roger Zelazny, a co-author on the post-apocalyptic science fiction novel Deus Irae (1976), also recalled the confusion of the audience after the speech. At Metz, Zelazny encountered numerous fans engaged in heated arguments over the meaning of the speech. One person told Zelazny that he thought Dick intended to start a new


id: imaginary-time-20260505-0
file: data/en.wikipedia.org/wiki/Imaginary_time-0.md
category: reference
title: Imaginary time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Imaginary_time
date_saved: 2026-05-05T11:14:13.037583+00:00
instance: kb-cron
parent: imaginary-time-20260505-0
summary:
Imaginary time is a mathematical representation of time that appears in some approaches to special relativity and quantum mechanics. It finds uses in certain cosmological theories. Mathematically, imaginary time is real time which has undergone a Wick rotation so that its coordinates are multiplied by the imaginary unit i. Imaginary time is not imaginary in the sense that it is unreal or made-up; it is simply expressed in terms of imaginary numbers. == Origins == In mathematics, the imaginary unit i {\displaystyle i} is − 1 {\displaystyle {\sqrt {-1}}} , such that i 2 {\displaystyle i^{2}} is defined to be − 1 {\displaystyle -1} . A number which is a direct multiple of i {\displaystyle i} is known as an imaginary number. A number that is the sum of an imaginary number and a real number is known as a complex number. In certain physical theories, periods of time are multiplied by i {\displaystyle i} in this way. Mathematically, an imaginary time period τ {\textstyle \tau } may be obtained from real time t {\textstyle t} via a Wick rotation by π / 2 {\textstyle \pi /2} in the complex plane: τ = i t {\textstyle \tau =it} . Stephen


id: immediacy-philosophy-20260505-0
file: data/en.wikipedia.org/wiki/Immediacy_(philosophy)-0.md
category: reference
title: Immediacy (philosophy)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Immediacy_(philosophy)
date_saved: 2026-05-05T11:14:14.226570+00:00
instance: kb-cron
parent: immediacy-philosophy-20260505-0
summary:
Immediacy is a philosophical concept related to time and temporal perspectives, both visual, and cognitive. Considerations of immediacy reflect on how we experience the world and what reality is. It implies a direct experience of an event or object bereft of any intervening medium. An example would be looking at a painting, losing awareness of the medium, and seeing the depiction as real. The medium is an important concept, and somewhat paradoxical, as it is both necessary and yet forgotten. Plato deals with a similar concept in the purity of experience. He tells us that speech is more immediate than writing, because the words emerge more directly from the speaker's mind. Immediacy also possesses characteristics of both of the homophonic heterographs 'immanent' and 'imminent', and what entails to both within ontology. Immediacy also relates to the philosophy of phenomenology, as they are schools of thought which both concern subjective perceptions of objects and time.


id: moving-spotlight-theory-of-time-20260505-0
file: data/en.wikipedia.org/wiki/Moving_spotlight_theory_of_time-0.md
category: reference
title: Moving spotlight theory of time
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Moving_spotlight_theory_of_time
date_saved: 2026-05-05T11:14:15.388049+00:00
instance: kb-cron
parent: moving-spotlight-theory-of-time-20260505-0
summary:
The moving spotlight theory of time is a theory of time which says that the complete history of the world exists (in much the same sense as the block universe, that is, past, present, and future all exist), but that there is an absolute, objective present moment. On this view, what is present really changes as time passes. This is a "moving spotlight" theory because the objective present "moves" through the block analogous to how a spotlight might traverse (e.g.) a row of houses in a street. This view is suggested, though not endorsed, by C.D. Broad in his Scientific Thought (1923). (Broad endorses the growing block theory of time, though this view can trace it roots further back to Samuel Alexander.) Moving spotlight theory and growing block theory are both taken as intermediary positions between either presentism and eternalism, or the A-theory and B-theory of time. It is common to see the moving spotlight theory described as a "non-presentist A-theory." The moving spotlight theory accepts the dynamic thesis of the A-theory that time really passes, what is objectively present changes, and accepts the static ontology of the B-theory that past, present, and future entities exist: the totality of what


id: non-simultaneity-20260505-0
file: data/en.wikipedia.org/wiki/Non-simultaneity-0.md
category: reference
title: Non-simultaneity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Non-simultaneity
date_saved: 2026-05-05T11:14:16.563486+00:00
instance: kb-cron
parent: non-simultaneity-20260505-0
summary:
Non-simultaneity or nonsynchronism (German: Ungleichzeitigkeit, sometimes also translated as non-synchronicity) is a concept in the writings of Ernst Bloch which denotes the time lag, or uneven temporal development, produced in the social sphere by the processes of capitalist modernization and/or the incomplete nature of those processes. The term, especially in the phrase "the simultaneity of the non-simultaneous", has been used subsequently in predominantly Marxist theories of modernity, world-systems, postmodernity and globalization. == In the work of Ernst Bloch == The phrase "the non-simultaneity of the simultaneous" (die 'Ungleichzeitigkeit' des Gleichzeitigen) was first used by the German art historian Wilhelm Pinder in his 1926 book Das Problem der Generation in der Kunstgeschichte Europas ("The Problem of Generation in European Art History"). Bloch's principal use of the term "non-simultaneity" was in an essay from 1932 which attempted to explain the rise and popularity of Nazism in Germany in the light of the capitalist economic crisis of the Great Depression and which became a chapter of his influential 1935 study Heritage of our Times (Erbschaft dieser Zeit). The essay's central idea is that heterogeneous stages of social and economic development coexist simultaneously in 1930s Germany. Because of uneven modernization, Bloch argues, there remained


id: non-simultaneity-20260505-1
file: data/en.wikipedia.org/wiki/Non-simultaneity-1.md
category: reference
title: Non-simultaneity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Non-simultaneity
date_saved: 2026-05-05T11:14:16.563486+00:00
instance: kb-cron
parent: non-simultaneity-20260505-0
summary:
The more production comes to rest on exchange value, hence on exchange, the more important do the physical conditions of exchange — the means of communication and transport — become for the costs of circulation. Capital by its nature drives beyond every spatial barrier. Thus the creation of the physical conditions of exchange — of the means of communication and transport — the annihilation of space by time — becomes an extraordinary necessity for it. At the same time, Marx showed himself to be acutely aware of the resistances to this overcoming of spatio-temporal barriers, and, more importantly, to the fact that capitalism itself generates its own resistances, or contradictions, to the universalization of its mode of production: But from the fact that capital posits every such limit as a barrier and hence gets ideally beyond it, it does not by any means follow that it has really overcome it, and, since every such barrier contradicts its character, its production moves in contradictions which are constantly overcome but just as constantly posited. Furthermore. The universality towards which it irresistibly strives encounters barriers in its own nature, which will, at a certain stage of its development, allow it to be recognized


id: non-simultaneity-20260505-2
file: data/en.wikipedia.org/wiki/Non-simultaneity-2.md
category: reference
title: Non-simultaneity
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Non-simultaneity
date_saved: 2026-05-05T11:14:16.563486+00:00
instance: kb-cron
parent: non-simultaneity-20260505-0
summary:
Modernism must thus be seen as uniquely corresponding to an uneven moment of social development, or to what Ernst Bloch called the "simultaneity of the nonsimultaneous," the "synchronicity of the nonsynchronous" (Gleichzeitigkeit des Ungleichzeitigen): the coexistence of realities from radically different moments of history — handicrafts alongside the great cartels, peasant fields with the Krupp factories or the Ford plant in the distance. Jameson goes on, however, to argue that with the advent of postmodernity and its attendant postmodernisms, the "uneven moment" of modernity has been completely replaced by the mass standardization and homogenization of the third, multinational, phase of capitalist development: the postmodern must be characterized as a situation in which the survival, the residue, the holdover, the archaic, has finally been swept away without a trace. In the postmodern, then, the past itself has disappeared (along with the well-known "sense of the past" or historicity and collective memory). Where its buildings still remain, renovation and restoration allow them to be transferred to the present in their entirety as those other, very different and postmodern things called simulacra. Everything is now organized and planned; nature has been triumphantly blotted out, along with peasants, petit-bourgeois commerce, handicraft, feudal aristocracies and


id: past-20260505-0
file: data/en.wikipedia.org/wiki/Past-0.md
category: reference
title: Past
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Past
date_saved: 2026-05-05T11:14:17.747415+00:00
instance: kb-cron
parent: past-20260505-0
summary:
The past is the set of all events that occurred before a given point in time. The past is contrasted with and defined by the present and the future. The concept of the past is derived from the linear fashion in which human observers experience time, and is accessed through memory and recollection. In addition, humans have recorded the past since the advent of written language. In English, the word past was one of the many variant forms and spellings of passed, the past participle of the Middle English verb passen (whence Modern English pass), among ypassed, ypassyd, i-passed, passyd, passid, pass'd, paste, etc. It developed into an adjective and preposition in the 14th century, and a noun (as in the past or a past, through ellipsis with the adjective past) in the 15th century. == Grammar == In English grammar, actions are classified according to one of the following twelve verb tenses: past (past, uses of English verb forms, past perfect, or past perfect continuous), present (present, present continuous, present perfect, or present perfect continuous), or future (future, future continuous, future perfect, or future perfect continuous). The past tense refers to actions that have already happened. For example, "she


id: past-hypothesis-20260505-0
file: data/en.wikipedia.org/wiki/Past_hypothesis-0.md
category: reference
title: Past hypothesis
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Past_hypothesis
date_saved: 2026-05-05T11:14:18.928263+00:00
instance: kb-cron
parent: past-hypothesis-20260505-0
summary:
In cosmology, the past hypothesis is a fundamental law of physics that postulates that the universe started in a low-entropy state, in accordance with the second law of thermodynamics. The second law states that any closed system follows the arrow of time, meaning its entropy never decreases. Applying this idea to the entire universe, the hypothesis argues that the universe must have started from a special event with less entropy than is currently observed, in order to preserve the arrow of time globally. This idea has been discussed since the development of statistical mechanics, but the term "past hypothesis" was coined by philosopher David Albert in 2000. Philosophical and theoretical efforts focus on trying to explain the consistency and the origin of the postulate. The past hypothesis is an exception to the principle of indifference, according to which every possible microstate within a certain macrostate would have an equal probability. The past hypothesis allows only those microstates that are compatible with a much-lower-entropy past, although these states are assigned equal probabilities. If the principle of indifference is applied without taking into account the past hypothesis, a low- or medium-entropy state would have likely evolved both from and toward higher-entropy macrostates,


id: perspectival-realism-20260505-0
file: data/en.wikipedia.org/wiki/Perspectival_realism-0.md
category: reference
title: Perspectival realism
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Perspectival_realism
date_saved: 2026-05-05T11:14:20.083010+00:00
instance: kb-cron
parent: perspectival-realism-20260505-0
summary:
In Caspar Hare's theory of perspectival realism, there is a defining intrinsic property that the things that are in perceptual awareness have. Consider seeing object A but not object B. Of course, we can say that the visual experience of A is present to you, and no visual experience of B is present to you. But, it can be argued, this misses the fact that the visual experience of A is simply present, not relative to anything. This is what Hare's perspectival realism attempts to capture, resulting in a weak version of metaphysical solipsism. As Hare points out, the same type of argument is often used in the philosophy of time to support theories such as presentism. Of course, we can say that A is happening on [insert today's date]. But, it can be argued, this misses the fact that A is simply happening (right now), not relative to anything. Hare's theory of perspectival realism is closely related to his theory of egocentric presentism. Several other philosophers have written reviews of Hare's work on this topic. == See also == Metaphysical subjectivism Centered worlds Benj Hellie's vertiginous question J.J. Valberg's personal horizon == References == == External links == Hare,


id: philosophy-of-time-society-20260505-0
file: data/en.wikipedia.org/wiki/Philosophy_of_Time_Society-0.md
category: reference
title: Philosophy of Time Society
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Philosophy_of_Time_Society
date_saved: 2026-05-05T11:14:21.247470+00:00
instance: kb-cron
parent: philosophy-of-time-society-20260505-0
summary:
The Philosophy of Time Society is an organization which grew out of a National Endowment for the Humanities Summer Seminar on the Philosophy of Time offered by George N. Schlesinger in 1991. The organization itself was formed in 1993. Its stated goal is "to promote the study of the philosophy of time from a broad analytic perspective, and to provide a forum as an affiliated group with the American Philosophical Association, to discuss the issues in and related to the philosophy of time." The current President of the Society is Nina Emery. The Philosophy of Time Society's meetings are held at the division meetings of the American Philosophical Association. In the past, they have included many notable scholars such as Craig Callender, L. A. Paul, Robin Le Poidevin, Ned Markosian, D. H. Mellor, John Perry, Theodore Sider, Michael Tooley, and Dean Zimmerman. Topics of papers have varied widely. == References == == External links == Philosophy of Time Society George Schlesinger Memorial Site


id: physical-cosmology-20260505-0
file: data/en.wikipedia.org/wiki/Physical_cosmology-0.md
category: reference
title: Physical cosmology
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physical_cosmology
date_saved: 2026-05-05T11:14:22.441984+00:00
instance: kb-cron
parent: physical-cosmology-20260505-0
summary:
Physical cosmology is a branch of physics concerned with modeling the universe based on the laws of physics. A cosmological model provides a mathematical description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood. Physical cosmology, as it is now understood, began in 1915 with the development of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond the Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding. These advances made it possible to speculate about the origin of the universe, and allowed the establishment of the Big Bang theory, by Georges Lemaître, as the leading cosmological model. A few researchers still advocate a handful of alternative cosmologies; however, most cosmologists agree that the Big Bang theory best explains the observations. Dramatic advances in observational cosmology since


id: physical-cosmology-20260505-1
file: data/en.wikipedia.org/wiki/Physical_cosmology-1.md
category: reference
title: Physical cosmology
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physical_cosmology
date_saved: 2026-05-05T11:14:22.441984+00:00
instance: kb-cron
parent: physical-cosmology-20260505-0
summary:
== Energy of the cosmos == The lightest chemical elements, primarily hydrogen and helium, were created during the Big Bang through the process of nucleosynthesis. In a sequence of stellar nucleosynthesis reactions, smaller atomic nuclei are then combined into larger atomic nuclei, ultimately forming stable iron group elements such as iron and nickel, which have the highest nuclear binding energies. The net process results in a later energy release, meaning subsequent to the Big Bang. Such reactions of nuclear particles can lead to sudden energy releases from cataclysmic variable stars such as novae. Gravitational collapse of matter into black holes also powers the most energetic processes, generally seen in the nuclear regions of galaxies, forming quasars and active galaxies. Cosmologists cannot explain all cosmic phenomena exactly, such as those related to the accelerating expansion of the universe, using conventional forms of energy. Instead, cosmologists propose a new form of energy called dark energy that permeates all space. One hypothesis is that dark energy is just the vacuum energy, a component of empty space that is associated with the virtual particles that exist due to the uncertainty principle. There is no clear way to define the total energy in the universe


id: physical-cosmology-20260505-2
file: data/en.wikipedia.org/wiki/Physical_cosmology-2.md
category: reference
title: Physical cosmology
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physical_cosmology
date_saved: 2026-05-05T11:14:22.441984+00:00
instance: kb-cron
parent: physical-cosmology-20260505-0
summary:
== Areas of study == Below, some of the most active areas of inquiry in cosmology are described, in roughly chronological order. This does not include all of the Big Bang cosmology, which is presented in Timeline of the Big Bang. === Very early universe === The early, hot universe appears to be well explained by the Big Bang from roughly 10−33 seconds onwards, but there are several problems. One is that there is no compelling reason, using current particle physics, for the universe to be flat, homogeneous, and isotropic (see the cosmological principle). Moreover, grand unified theories of particle physics suggest that there should be magnetic monopoles in the universe, which have not been found. These problems are resolved by a brief period of cosmic inflation, which drives the universe to flatness, smooths out anisotropies and inhomogeneities to the observed level, and exponentially dilutes the monopoles. The physical model behind cosmic inflation is extremely simple, but it has not yet been confirmed by particle physics, and there are difficult problems reconciling inflation and quantum field theory. Some cosmologists think that string theory and brane cosmology will provide an alternative to inflation. Another major problem in cosmology is what caused


id: physical-cosmology-20260505-3
file: data/en.wikipedia.org/wiki/Physical_cosmology-3.md
category: reference
title: Physical cosmology
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physical_cosmology
date_saved: 2026-05-05T11:14:22.441984+00:00
instance: kb-cron
parent: physical-cosmology-20260505-0
summary:
Understanding the formation and evolution of the largest and earliest structures (i.e., quasars, galaxies, clusters and superclusters) is one of the largest efforts in cosmology. Cosmologists study a model of hierarchical structure formation in which structures form from the bottom up, with smaller objects forming first, while the largest objects, such as superclusters, are still assembling. One way to study structure in the universe is to survey the visible galaxies, in order to construct a three-dimensional picture of the galaxies in the universe and measure the matter power spectrum. This is the approach of the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey. Another tool for understanding structure formation is simulations, which cosmologists use to study the gravitational aggregation of matter in the universe, as it clusters into filaments, superclusters and voids. Most simulations contain only non-baryonic cold dark matter, which should suffice to understand the universe on the largest scales, as there is much more dark matter in the universe than visible, baryonic matter. More advanced simulations are starting to include baryons and study the formation of individual galaxies. Cosmologists study these simulations to see if they agree with the galaxy surveys, and to understand any discrepancy.


id: physical-cosmology-20260505-4
file: data/en.wikipedia.org/wiki/Physical_cosmology-4.md
category: reference
title: Physical cosmology
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physical_cosmology
date_saved: 2026-05-05T11:14:22.441984+00:00
instance: kb-cron
parent: physical-cosmology-20260505-0
summary:
=== Gravitational waves === Gravitational waves are ripples in the curvature of spacetime that propagate as waves at the speed of light, generated in certain gravitational interactions that propagate outward from their source. Gravitational-wave astronomy is an emerging branch of observational astronomy which aims to use gravitational waves to collect observational data about sources of detectable gravitational waves such as binary star systems composed of white dwarfs, neutron stars, and black holes; and events such as supernovae, and the formation of the early universe shortly after the Big Bang. In 2016, the LIGO Scientific Collaboration and Virgo Collaboration teams announced that they had made the first observation of gravitational waves, originating from a pair of merging black holes using the Advanced LIGO detectors. On 15 June 2016, a second detection of gravitational waves from coalescing black holes was announced. Besides LIGO, many other gravitational-wave observatories (detectors) are under construction. === Other areas of inquiry === Cosmologists also study: Whether primordial black holes were formed in our universe, and what happened to them. Detection of cosmic rays with energies above the GZK cutoff, and whether it signals a failure of special relativity at high energies. The equivalence principle, whether or not


id: physics-aristotle-20260505-0
file: data/en.wikipedia.org/wiki/Physics_(Aristotle)-0.md
category: reference
title: Physics (Aristotle)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physics_(Aristotle)
date_saved: 2026-05-05T11:14:23.733233+00:00
instance: kb-cron
parent: physics-aristotle-20260505-0
summary:
The Physics (Ancient Greek: Φυσικής ἀκρόασις, romanized: Physikḗs akróasis, or: Φυσικής ακροάσεως, Physikḗs akroáseōs; Latin: Physica or Naturales Auscultationes, possibly meaning "Lectures on nature") is a named text, written in ancient Greek, collated from a collection of surviving manuscripts known as the Corpus Aristotelicum, attributed to the 4th-century BC philosopher Aristotle. == The meaning of physics in Aristotle == It is a collection of treatises or lessons that deals with the most general (philosophical) principles of natural or moving things, both living and non-living, rather than physical theories (in the modern sense) or investigations of the particular contents of the universe. The chief purpose of the work is to discover the principles and causes of (and not merely to describe) change, or movement, or motion (κίνησις kinesis), especially that of natural wholes (mostly living things, but also inanimate wholes like the cosmos). In the conventional Andronicean ordering of Aristotle's works, it stands at the head of, as well as being foundational to, the long series of physical, cosmological and biological treatises, whose ancient Greek title, τὰ φυσικά, means "the [writings] on nature" or "natural philosophy". == Description of the content == The Physics is composed of eight books, which are


id: physics-aristotle-20260505-1
file: data/en.wikipedia.org/wiki/Physics_(Aristotle)-1.md
category: reference
title: Physics (Aristotle)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physics_(Aristotle)
date_saved: 2026-05-05T11:14:23.733233+00:00
instance: kb-cron
parent: physics-aristotle-20260505-0
summary:
The necessary in nature, then, is plainly what we call by the name of matter, and the changes in it. Both causes must be stated by the physicist, but especially the end; for that is the cause of the matter, not vice versa; and the end is 'that for the sake of which', and the beginning starts from the definition or essence… In chapter 3, Aristotle presents his theory of the four causes (material, efficient, formal, and final). Material cause explains what something is made of (for example, the wood of a house), formal cause explains the form which a thing follows to become that thing (the plans of an architect to build a house), efficient cause is the actual source of the change (the physical building of the house), and final cause is the intended purpose of the change (the final product of the house and its purpose as a shelter and home). Of particular importance is the final cause or purpose (telos). It is a common mistake to conceive of the four causes as additive or alternative forces pushing or pulling; in reality, all four are needed to explain (7.198a22-25). What we typically mean by cause in the


id: physics-aristotle-20260505-2
file: data/en.wikipedia.org/wiki/Physics_(Aristotle)-2.md
category: reference
title: Physics (Aristotle)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physics_(Aristotle)
date_saved: 2026-05-05T11:14:23.733233+00:00
instance: kb-cron
parent: physics-aristotle-20260505-0
summary:
=== Book VII (Η; 241a25–250b7) === Book VII briefly deals with the relationship of the moved to his mover, which Aristotle describes in substantial divergence with Plato's theory of the soul as capable of setting itself in motion (Laws book X, Phaedrus, Phaedo). Everything which moves is moved by another. He then tries to correlate the species of motion and their speeds, with the local change (locomotion, phorà) as the most fundamental to which the others can be reduced. Book VII.1-3 also exist in an alternative version, not included in the Bekker edition. === Book VIII (Θ; 250a14–267b26) === Book VIII (which occupies almost a fourth of the entire Physics, and probably constituted originally an independent course of lessons) discusses two main topics, though with a wide deployment of arguments: the time limits of the universe, and the existence of a Prime Mover — eternal, indivisible, without parts and without magnitude. Isn't the universe eternal, has it had a beginning, will it ever end? Aristotle's response, as a Greek, could hardly be affirmative, never having been told of a creatio ex nihilo, but he also has philosophical reasons for denying that motion had not always existed, on the grounds of


id: physics-aristotle-20260505-3
file: data/en.wikipedia.org/wiki/Physics_(Aristotle)-3.md
category: reference
title: Physics (Aristotle)
tags: science, encyclopedia
source_url: https://en.wikipedia.org/wiki/Physics_(Aristotle)
date_saved: 2026-05-05T11:14:23.733233+00:00
instance: kb-cron
parent: physics-aristotle-20260505-0
summary:
=== Classical and medieval commentaries on the Physics === A commentary differs from a note in being a distinct work analyzing the language and subsumed concepts of some other work classically notable. A note appears within the annotated work on the same page or in a separate list. Commentaries are typically arranged by lemmas, or quotes from the notable work, followed by an analysis of the author of the commentary. The commentaries on every work of Aristotle are a vast and mainly unpublished topic. They extend continuously from the death of the philosopher, representing the entire history of Graeco-Roman philosophy. There are thousands of commentators and commentaries known wholly or more typically in fragments of manuscripts. The latter especially occupy the vaults of institutions formerly responsible for copying them, such as monasteries. The process of publishing them is slow and ongoing. Below is a brief representative bibliography of published commentaries on Aristotle's Physics available on or through the Internet. Like the topic itself, they are perforce multi-cultural, but English has been favored, as well as the original languages, ancient Greek and Latin. === Some modern commentaries, monographs and articles === == Further reading == Books Die Aristotelische Physik, W. Wieland,


