Sunrise shown in time lapse. Sunrise is the instant at which the upper edge of the Sun appears above the Horizon in the East. Time-lapse photography is a Cinematography technique whereby each Film frame is captured at a rate much slower than it will be played back
The motions of Sun and Moon have demonstrated and symbolized time throughout humanity's existence. The Sun (Sol is the Star at the center of the Solar System. ^[1]

The flow of sand in an hourglass can be used to keep track of elapsed time. An hourglass, also known as a sandglass, sand timer or sand clock, is a device for the measurement of Time. It also concretely represents the present as being between the past and the future. The present is the Time that is perceived directly not as a recollection or a speculation PAST (short for Polska Akcyjna Spółka Telefoniczna, Polish Telephone Joint-stock Company) was a Polish telephone operator in the period between World War I The future is commonly understood to contain all events that have yet to occur It was made in the 17th century.

Time is a component of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects. Time has been a major subject of religion, philosophy, and science, but defining time in a non-controversial manner applicable to all fields of study has consistently eluded the greatest scholars. A religion is a set of Tenets and practices often centered upon specific Supernatural and moral claims about Reality, the Cosmos Philosophy is the study of general problems concerning matters such as existence knowledge truth beauty justice validity mind and language Science (from the Latin scientia, meaning " Knowledge " or "knowing" is the effort to discover, and increase human understanding

In physics and other sciences, time is considered one of the few fundamental quantities. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. A set of fundamental units is a set of units for physical quantities from which every other unit can be generated ^[2] Time is used to define other quantities – such as velocity – and defining time in terms of such quantities would result in circularity of definition. In Physics, velocity is defined as the rate of change of Position. A circular definition is one that assumes a prior understanding of the term being defined ^[3] An operational definition of time, wherein one says that observing a certain number of repetitions of one or another standard cyclical event (such as the passage of a free-swinging pendulum) constitutes one standard unit such as the second, has a high utility value in the conduct of both advanced experiments and everyday affairs of life. An operational definition is a demonstration of a process &mdash such as a Variable, term, or object &mdash relative in terms of the specific Process The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units The operational definition leaves aside the question whether there is something called time, apart from the counting activity just mentioned, that flows and that can be measured. Investigations of a single continuum called space-time brings the nature of time into association with related questions into the nature of space, questions that have their roots in the works of early students of natural philosophy. SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another For the current in the 19th century German idealism see Naturphilosophie Natural philosophy or the philosophy of nature (from

Among prominent philosophers, there are two distinct viewpoints on time. One view is that time is part of the fundamental structure of the universe, a dimension in which events occur in sequence. The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy In mathematics the dimension of a Space is roughly defined as the minimum number of Coordinates needed to specify every point within it In Mathematics, a sequence is an ordered list of objects (or events Sir Isaac Newton subscribed to this realist view, and hence it is sometimes referred to as Newtonian time. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements Contemporary philosophical realism is the belief in a Reality that is completely Ontologically independent of our conceptual schemes linguistic practices beliefs In Physics, the concept of absolute time and absolute space are Hypothetical models in which time either runs at the same rate for all the observers in ^[4][5] The opposing view is that time does not refer to any kind of "container" that events and objects "move through", nor to any entity that "flows", but that it is instead part of a fundamental intellectual structure (together with space and number) within which humans sequence and compare events. Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another A number is an Abstract object, tokens of which are Symbols used in Counting and measuring. This second view, in the tradition of Gottfried Leibniz^[6] and Immanuel Kant,^[7][8] holds that time is neither an event nor a thing, and thus is not itself measurable. Immanuel Kant (ɪmanuəl kant 22 April 1724 12 February 1804 was an 18th-century German Philosopher from the Prussian city of Königsberg

Temporal measurement has occupied scientists and technologists, and was a prime motivation in navigation and astronomy. A technologist is a specialist that is trained to perform work in a field of Technology. Navigation is the process of reading and controlling the movement of a craft or vehicle from one place to another Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study Periodic events and periodic motion have long served as standards for units of time. Examples include the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum, and the beat of a heart. Currently, the international unit of time, the second, is defined as a certain number of hyperfine transitions in caesium atoms (see below). The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units In Atomic physics, hyperfine coupling is the weak magnetic interaction between Electrons and nuclei. Caesium or cesium (ˈsiːziəm is the Chemical element with the symbol Cs and Atomic number 55 Time is also of significant social importance, having economic value ("time is money") as well as personal value, due to an awareness of the limited time in each day and in human lifespans. The time value of money is based on the premise that an Investor prefers to receive a payment of a fixed amount of money today rather than an equal amount in the future In Biological psychology, awareness comprises a human's or an animal's perception and Cognitive reaction to a condition or event Life expectancy is the average number of years of life remaining at a given age

Temporal measurement

Temporal measurement, or chronometry, takes two distinct period forms: the calendar, a mathematical abstraction for calculating extensive periods of time,^[9] and the clock, a concrete mechanism that counts the ongoing passage of time. Chronometry (from Greek χρόνος "time" and μέτρηση "measurement" is the science of the measurement of Time, The word Calendar consist of two words 1 Cal ( in Pashto means Year in Hindi and Persian is Sal- also means Year Circadian Locomotor Output Cycles Kaput, or Clock is a gene which encodes proteins regulating Circadian rhythm. In day-to-day life, the clock is consulted for periods less than a day, the calendar, for periods longer than a day.

History of the calendar

Main article: Calendar

Artifacts from the Palaeolithic suggest that the moon was used to calculate time as early as 12,000, and possibly even 30,000 BP. The word Calendar consist of two words 1 Cal ( in Pashto means Year in Hindi and Persian is Sal- also means Year The term Paleolithic (or Palaeolithic) (from Greek παλαιός palaios, " Old " and λίθος Lithos, "stone" Before Present (BP years are a time scale used in Archaeology, Geology, and other scientific disciplines to specify when events in the past occurred ^[1]

The Sumerian civilization of approximately 2000 BC introduced the sexagesimal system based on the number 60. Sumer ( Sumerian: sux-Latn [[Ki (earth ki]]-[[EN (cuneiform en]]-'''ĝir15''', Akkadian: Šumeru; possibly Biblical Shinar Sexagesimal ( base-sixty) is a Numeral system with sixty as the base. 60 seconds in a minute, 60 minutes in an hour – and possibly a calendar with 360 (60x6) days in a year (with a few more days added on). Twelve also features prominently, with roughly 12 hours of day and 12 of night, and 12 months in a year (with 12 being 1/5 of 60).

The reforms of Julius Caesar in 45 BC put the Roman world on a solar calendar. The Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial A solar calendar is a Calendar whose dates indicate the position of the earth on its revolution around the Sun (or equivalently the apparent position of the sun moving This Julian calendar was faulty in that its intercalation still allowed the astronomical solstices and equinoxes to advance against it by about 11 minutes per year. The Julian calendar, a reform of the Roman calendar, was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 Ab urbe condita Intercalation is the insertion of a leap day week or month into some calendar years to make the calendar follow the seasons or moon phases Solstices occur twice a year when the tilt of the Earth's axis is most oriented toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes An equinox is the event of the Sun passing over the Earth's equator in its annual cycle Pope Gregory XIII introduced a correction in 1582; the Gregorian calendar was only slowly adopted by different nations over a period of centuries, but is today the one in most common use around the world. Pope Gregory XIII (January 7 1502 &ndash April 10 1585 born Ugo Boncompagni, was Pope from 1572 to 1585 The Gregorian calendar is the most widely used Calendar in the world today

History of time measurement devices

Horizontal sundial in Taganrog (1833)

Main article: History of timekeeping devices

See also: Clock

A large variety of devices have been invented to measure time. A sundial is a device that measures time by the position of the Sun. Taganrog (Таганро́г təgʌnˈrok is a seaport city in Rostov Oblast, Russia, located on the north shore of Taganrog For thousands of years devices have been used to measure and keep track of Time. Circadian Locomotor Output Cycles Kaput, or Clock is a gene which encodes proteins regulating Circadian rhythm. In the Physical sciences Quality assurance, and Engineering, Measurement is the activity of obtaining and comparing physical quantities The study of these devices is called horology. Horology (from Greek ώρα, "hour time" and λόγος Logos, "study speech" lit

An Egyptian device dating to c. This article is about the country of Egypt For a topic outline on this subject see List of basic Egypt topics. 1500 BC, similar in shape to a bent T-square, measured the passage of time from the shadow cast by its crossbar on a non-linear rule. A T-square is a Technical drawing instrument primarily a guide for drawing Horizontal lines on a Drafting table. The T was oriented eastward in the mornings. At noon, the device was turned around so that it could cast its shadow in the evening direction. Noon (also midday) is the hour of 1200 in an observer's local time zone or more loosely a time near the middle of the day when workers in many countries take a meal break ^[10]

A sundial uses a gnomon to cast a shadow on a set of markings which were calibrated to the hour. A sundial is a device that measures time by the position of the Sun. The gnomon is the part of a Sundial that casts the Shadow. Gnomon (γνώμων is an Ancient Greek word meaning "indicator" "one who The hour (symbol h) is a unit of Time. It is not an SI unit but is accepted for use with the SI The position of the shadow marked the hour in local time.

The most accurate timekeeping devices of the ancient world were the waterclock or clepsydra, one of which was found in the tomb of Egyptian pharaoh Amenhotep I (1525–1504 BC). A water clock or clepsydra ( Greek kleptein to steal; hydro water) is any timekeeper operated by means of a regulated flow of liquid into (inflow Amenhotep I (sometimes read as Amenophis I and meaning " Amun is satisfied" was the second Pharaoh of the 18th dynasty of Egypt They could be used to measure the hours even at night, but required manual timekeeping to replenish the flow of water. The Greeks and Chaldeans regularly maintained timekeeping records as an essential part of their astronomical observations. The Greeks ( Greek: Έλληνες) are a Nation and Ethnic group native to Greece, Cyprus and neighbouring regions Arab engineers in particular made improvements on the use of waterclocks up to the Middle Ages. ^[11]

A contemporary quartz watch

The hourglass uses the flow of sand to measure the flow of time. A quartz clock is a Clock that uses an Electronic oscillator that is regulated by a Quartz crystal to keep time An hourglass, also known as a sandglass, sand timer or sand clock, is a device for the measurement of Time. They were used in navigation. Ferdinand Magellan used 18 glasses on each ship for his circumnavigation of the globe (1522). Ferdinand Magellan (Fernão de Magalhães fɨɾˈnɐ̃ũ dɨ mɐgɐˈʎɐ̃ĩʃ Fernando de Magallanes (Spring 1480 &ndash April 27 1521 Mactan Island, Cebu ^[12]

Incense sticks and candles were, and are, commonly used to measure time in temples and churches across the globe. Waterclocks, and later, mechanical clocks, were used to mark the events of the abbeys and monasteries of the Middle Ages. Richard of Wallingford (1292–1336), abbot of St. For the Constable of Wallingford Castle see Richard of Wallingford (constable. Alban's abbey, famously built a mechanical clock as an astronomical orrery about 1330. Circadian Locomotor Output Cycles Kaput, or Clock is a gene which encodes proteins regulating Circadian rhythm. This article is on the mechanical device For the British peerage see Earl of Orrery. ^[13][14]

The English word clock probably comes from the Middle Dutch word "klocke" which is in turn derived from the mediaeval Latin word "clocca", which is ultimately derived from Celtic, and is cognate with French, Latin, and German words that mean bell. Circadian Locomotor Output Cycles Kaput, or Clock is a gene which encodes proteins regulating Circadian rhythm. A bell is a simple Sound -making device The bell is a Percussion instrument and an Idiophone. The passage of the hours at sea were marked by bells, and denoted the time (see ship's bells). A Ship's Bell is usually made of brass and has the ship's name engraved on it The hours were marked by bells in the abbeys as well as at sea.

A chip-scale atomic clock

Clocks can range from watches, to more exotic varieties such as the Clock of the Long Now. A watch is a timepiece that is made to be worn on a person The term now usually refers to a wristwatch, which is worn on the wrist with a strap or Bracelet. The Clock of the Long Now, also called the 10000-year clock, is a proposed mechanical Clock designed to keep time for 10000 years They can be driven by a variety of means, including gravity, springs, and various forms of electrical power, and regulated by a variety of means such as a pendulum. A pendulum is a mass that is attached to a pivot from which it can swing freely

A chronometer is a portable timekeeper that meets certain precision standards. A chronometer watch is a Watch tested and certified to meet certain precision standards Initially, the term was used to refer to the marine chronometer, a timepiece used to determine longitude by means of celestial navigation. A marine chronometer is a timekeeper precise enough to be used as a portable Time standard; it can therefore be used to determine Longitude by means of Celestial Longitude (ˈlɒndʒɪˌtjuːd or ˈlɒŋgɪˌtjuːd symbolized by the Greek character Lambda (λ is the east-west Geographic coordinate measurement Celestial navigation, also known as astronavigation, is a Position fixing technique that was devised to help sailors cross the featureless oceans without having to More recently, the term has also been applied to the chronometer watch, a wristwatch that meets precision standards set by the Swiss agency COSC. A chronometer watch is a Watch tested and certified to meet certain precision standards A watch is a timepiece that is made to be worn on a person The term now usually refers to a wristwatch, which is worn on the wrist with a strap or Bracelet. This article is about the Swiss Official Chronometer Testing Institute known by its French acronym of COSC.

The most accurate timekeeping devices are atomic clocks, which are accurate to seconds in many millions of years,^[15] and are used to calibrate other clocks and timekeeping instruments. An atomic clock is a type of Clock that uses an Atomic resonance Frequency standard as its timekeeping element Atomic clocks use the spin property of atoms as their basis, and since 1967, the International System of Measurements bases its unit of time, the second, on the properties of caesium atoms. Caesium or cesium (ˈsiːziəm is the Chemical element with the symbol Cs and Atomic number 55 SI defines the second as 9,192,631,770 cycles of that radiation which corresponds to the transition between two electron spin energy levels of the ground state of the ¹³³Cs atom.

Today, the Global Positioning System in coordination with the Network Time Protocol can be used to synchronize timekeeping systems across the globe. Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth The Network Time Protocol ( NTP) is a protocol for distributing the Coordinated Universal Time (UTC by means of synchronizing the clocks of computer systems

Definitions and standards

See also: Time standard and Orders of magnitude (time)

The SI base unit for time is the SI second. An Olympiad is a period of four years associated with the Olympic Games of Classical Greece. Lustrum, in Ancient Rome, was originally a Sacrifice for Expiation and Purification offered by one of the Censors of Rome in A decade is a period of 10 Years (since 1594 a factor of 10 difference between two numbers, or sometimes a set or a group of ten (since 1451 An indiction is any of the years in a 15-year cycle used to date medieval documents throughout Europe, both East and West Generation (from the Greek γενεά) also known as procreation, is the act of producing Offspring. A century (from the Latin centum, meaning one hundred is One hundred consecutive Years Centuries are numbered ordinally (e A millennium (pl millennia) is a period of Time equal to one thousand Years (from Latin la mille, thousand and la annum A time standard Seconds Years See also Natural history Geologic The International System of Units (SI defines seven dimensionally independent SI base units. The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units From the second, larger units such as the minute, hour and day are defined, though they are "non-SI" units because they do not use the decimal system, and also because of the occasional need for a leap-second. A minute is a Unit of measurement of Time or of Angle. The minute is a unit of Time equal to 1/60th of an Hour or 60 The hour (symbol h) is a unit of Time. It is not an SI unit but is accepted for use with the SI A day (symbol d is a unit of Time equivalent to 24 Hours and the duration of a single Rotation of planet Earth with respect to the A leap second is a one- Second adjustment that keeps broadcast standards for time of day close to mean solar time. They are, however, officially accepted for use with the International System. There are no fixed ratios between seconds and months or years as months and years have significant variations in length. The month is a unit of Time, used with Calendars which is approximately as long as some natural period related to the motion of the Moon; A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun ^[16]

The official SI definition of the second is as follows:^[16][17]

The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. Caesium or cesium (ˈsiːziəm is the Chemical element with the symbol Cs and Atomic number 55

At its 1997 meeting, the CIPM affirmed that this definition refers to a caesium atom in its ground state at a temperature of 0 K. ^[16] Previous to 1967, the second was defined as:

the fraction 1/31,556,925. 9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time. A tropical year (also known as a solar year) is the length of time that the Sun takes to return to the same position in the cycle of seasons as seen from Earth Ephemeris Time ( ET) is a time scale used in Ephemerides of celestial bodies in particular the Sun (as observed from the Earth Moon planets and other members of

The current definition of the second, coupled with the current definition of the metre, is based on the special theory of relativity, which affirms our space-time to be a Minkowski space. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS In Physics and Mathematics, Minkowski space (or Minkowski spacetime) is the mathematical setting in which Einstein's theory of Special relativity

World time

The measurement of time is so critical to the functioning of modern societies that it is coordinated at an international level. The basis for scientific time is a continuous count of seconds based on atomic clocks around the world, known as the International Atomic Time (TAI). An atomic clock is a type of Clock that uses an Atomic resonance Frequency standard as its timekeeping element International Atomic Time ( TAI, from the French name Temps Atomique International) is a high-precision atomic Time standard that tracks This is the yardstick for other time scales, including Coordinated Universal Time (UTC), which is the basis for civil time.

Earth is split up into a number of time zones. Most time zones are exactly one hour apart, and by convention compute their local time as an offset from UTC or Greenwich Mean Time. Greenwich Mean Time ( GMT) is a term originally referring to mean solar time at the Royal Observatory in Greenwich, London In many locations these offsets vary twice yearly due to daylight saving time transitions. Daylight saving time ( DST

Sidereal time

Sidereal time is the measurement of time relative to a distant star (instead of solar time that is relative to the sun). Sidereal time is a measure of the position of the Earth in its rotation around its axis or time measured by the apparent Diurnal motion of the Vernal equinox It is used in astronomy to predict when a star will be overhead. Due to the rotation of the earth around the sun a sidereal day is slightly less than a solar day.

Chronology

Main article: Chronology

Another form of time measurement consists of studying the past. Definition A chronology may be either relative &mdashthat is locating related events relative to each other&mdashor ''absolute'' &mdashlocating PAST (short for Polska Akcyjna Spółka Telefoniczna, Polish Telephone Joint-stock Company) was a Polish telephone operator in the period between World War I Events in the past can be ordered in a sequence (creating a chronology), and be put into chronological groups (periodization). Definition A chronology may be either relative &mdashthat is locating related events relative to each other&mdashor ''absolute'' &mdashlocating Periodization is the attempt to categorize or divide Time into discrete named blocks One of the most important systems of periodization is geologic time, which is a system of periodizing the events that shaped the Earth and its life. The geologic time scale is a chronologic schema (or idealized Model) relating Stratigraphy to time that is used by Geologists and other EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Chronology, periodization, and interpretation of the past are together known as the study of history. History is the study of the past particularly the written record Those who study history as a Profession are called Historians Etymology

Allegorical woodcut of Time, who "revealeth all things", guiding his daughter Truth away from the demon of Hypocrisy. John Byddell, 1535.

Time in religion and mythology

Further information: Category:Time and fate deities

In the Old Testament book Ecclesiastes, traditionally but not critically ascribed to Solomon (970–928 BC), time (as the Hebrew word עדן, זמן `iddan(time) zĕman(season) is often translated) was traditionally regarded as a medium for the passage of predestined events. In Western Christianity, the Old Testament refers to the books that form the first of the two-part Christian Biblical canon. Ecclesiastes (often abbreviated Ecc) (קֹהֶלֶת Kohelet, variously transliterated as Qoheleth, Göhalath, Koheles, Koheleth King Solomon ( Ge'ez: ስለሞን Arabic: ar سليمان, Sulayman, all from the Triliteral root S-L-M, "peace" Predestination (also linked with Foreknowledge) is a religious concept which involves the relationship between God and His creation (Another word, זמן zman, was current as meaning time fit for an event, and is used as the modern Hebrew equivalent to the English word "time". )

Hindu units of time shown logarithmically

There is an appointed time (zman) for everything. Hinduism’s understanding of time is as grandiose as time itself Definition and base Logarithmic scales are either defined for ratios of the underlying quantity or one has to agree to measure And there is a time (’êth) for every event under heaven–
A time (’êth) to give birth, and a time to die; A time to plant, and a time to uproot what is planted.
A time to kill, and a time to heal; A time to tear down, and a time to build up.
A time to weep, and a time to laugh; A time to mourn, and a time to dance.
A time to throw stones, and a time to gather stones; A time to embrace, and a time to shun embracing.
A time to search, and a time to give up as lost; A time to keep, and a time to throw away.
A time to tear apart, and a time to sew together; A time to be silent, and a time to speak.
A time to love, and a time to hate; A time for war, and a time for peace. – Ecclesiastes 3:1–8

Linear and cyclical time

See also: Time Cycles and Wheel of time

In general, the Judaeo-Christian concept, based on the Bible, is that time is linear, with a beginning, the act of creation by God. Time cycles signify a 360 degree circular or eliptical rotation orbit or journey in time typically of an object such as a planet or moon The wheel of time or wheel of history is a concept in several religions and philosophies notably religions of Indian origin such as Buddhism and Hinduism Judeo-Christian (or Judaeo-Christian, sometimes written as Judæo-Christian) is a term used to describe the body of concepts and values which are thought to be held Etymology According to the Online Etymology Dictionary, the word bible is from Latin biblia, traced from the same word through Medieval Latin and Late Latin God is the principal or sole Deity in Religions and other belief systems that worship one deity. The Christian view assumes also an end, the eschaton, expected to happen when Christ returns to earth in the Second Coming to judge the living and the dead. A Christian is a person who adheres to Christianity, a monotheistic Religion centered on the life and teachings of Jesus of Nazareth Christ is the English term for the Greek ( Khristós) meaning "the anointed " In Christianity, the Second Coming is the anticipated return of Jesus Christ from Heaven to earth an event that will fulfill aspects of Messianic This will be the consummation of the world and time. St Augustine's City of God was the first developed application of this concept to world history. The Christian view is that God is uncreated and eternal so that He and the supernatural world are outside time and exist in eternity. While in the popular mind eternity often simply means existing for a limitless amount of Time, many have used it to refer to a timeless existence altogether outside of

Ancient cultures such as Incan, Mayan, Hopi, and other Native American Tribes, plus the Babylonian, Ancient Greek, Hindu, Buddhist, Jainist, and others have a concept of a wheel of time, that regards time as cyclical and quantic consisting of repeating ages that happen to every being of the Universe between birth and extinction. The Inca Empire (or Inka Empire) was the largest empire in Pre-Columbian America. The Hopi are Native American people who primarily live on the 12635 km² (2531 Babylonia was an Amorite state in lower Mesopotamia (modern southern Iraq) with Babylon as its capital The Ancient Greek language is the historical stage in the development of the Hellenic language family spanning the Archaic (c A Hindu ( Devanagari: हिन्दू is an adherent of the philosophies and scriptures of Hinduism, a set of religious, Philosophical Buddhism is a family of beliefs and practices Jainism, traditionally known as Jain Dharma / Shraman Dharma (जैन धर्म is an ancient religion of India. The wheel of time or wheel of history is a concept in several religions and philosophies notably religions of Indian origin such as Buddhism and Hinduism Social cycle theories are one of the earliest Social theories in Sociology.

Time in philosophy

Main article: Philosophy of space and time

The earliest recorded philosophy of time was expounded by Ptahhotep, who lived c. Philosophy of space and time is the branch of Philosophy concerned with the issues surrounding the Ontology, Epistemology, and character of Space Ptahhotep, sometimes known as Ptahhotpe or Ptah-Hotep, was an ancient Egyptian official during the 24th century BC. 2650–2600 BC. He said: "Do not lessen the time of following desire, for the wasting of time is an abomination to the spirit. "

Ancient Greek philosophers, including Parmenides and Heraclitus, wrote essays on the nature of time. Parmenides of Elea ( Greek:, early 5th century BC was an Ancient Greek Philosopher born in Elea, a Greek city on the southern coast of Heraclitus of Ephesus ( Ancient Greek: &mdash grc-Latn ''Hērákleitos ho Ephésios'' English Heraclitus the Ephesian) (ca ^[18]

In Book 11 of St. Augustine's Confessions, he ruminates on the nature of time, asking, "What then is time? If no one asks me, I know: if I wish to explain it to one that asketh, I know not. " He settles on time being defined more by what it is not than what it is. ^[19]

Isaac Newton believed time and space form a container for events, which is as real as the objects it contains. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another For other uses of Object see Object. In Philosophy, an object is a thing an Entity, or a Being.

Absolute, true, and mathematical time, in and of itself and of its own nature, without reference to anything external, flows uniformly and by another name is called duration. Relative, apparent, and common time is any sensible and external measure (precise or imprecise) of duration by means of motion; such a measure – for example, an hour, a day, a month, a year – is commonly used instead of true time.

– Principia^[20]

In contrast to Newton's belief in absolute space, and a precursor to Kantian time, Leibniz believed that time and space are relational. ^[21] The differences between Leibniz's and Newton's interpretations came to a head in the famous Leibniz-Clarke Correspondence. The Leibniz-Clarke correspondence was a Scientific, Theological and Philosophical Debate conducted by Epistolary means between the Leibniz thought of time as a fundamental part of an abstract conceptual framework, together with space and number, within which we sequence events, quantify their duration, and compare the motions of objects. An abstract structure is a Formal object that is defined by a set of laws properties and relationships in a way that is logically if not always historically independent of Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another A number is an Abstract object, tokens of which are Symbols used in Counting and measuring. Quantity is a kind of property which exists as magnitude or multitude In this view, time does not refer to any kind of entity that "flows," that objects "move through," or that is a "container" for events.

Immanuel Kant, in the Critique of Pure Reason, described time as an a priori intuition that allows us (together with the other a priori intuition, space) to comprehend sense experience. Immanuel Kant (ɪmanuəl kant 22 April 1724 12 February 1804 was an 18th-century German Philosopher from the Prussian city of Königsberg The Critique of Pure Reason (Kritik der reinen Vernunft by Immanuel Kant, first published in 1781, second edition 1787, is one "A priori" redirects here For other uses see A priori. Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another ^[22] With Kant, neither space nor time are conceived as substances, but rather both are elements of a systematic mental framework that necessarily structures the experiences of any rational agent, or observing subject. Substance theory, or substance attribute theory, is an ontological theory about objecthood, positing that a substance is distinct from its A framework is a basic conceptual structure used to solve or address complex issues Spatial measurements are used to quantify how far apart objects are, and temporal measurements are used to quantify how far apart events occur. Measurement is the process of estimating the magnitude of some attribute of an object such as its length or weight relative to some standard ( unit of measurement) such as Quantity is a kind of property which exists as magnitude or multitude For other uses of Object see Object. In Philosophy, an object is a thing an Entity, or a Being. A phenomenon (from Greek φαινόμενoν, pl φαινόμενα - phenomena) is any observable occurrence

In Existentialism, time is considered fundamental to the question of being, in particular by the philosopher Martin Heidegger. Existentialism is a philosophical doctrine which posits that individuals create the meaning and essence of their lives and that this essence follows from their existence Disambiguation For the Wigwam album see Being (album, for spiritual or religious beingness, see Ego (spirituality Martin Heidegger ( September 26, 1889 &ndash May 26, 1976) (ˈmaɐ̯tiːn ˈhaɪ̯dɛgɐ was an influential German philosopher (See Ontology). In Philosophy, ontology (from the Greek, genitive: of being (part

Henri Bergson believed that time was neither a real homogeneous medium nor a mental construct, but possesses what he referred to as Duration. Duration, in Bergson's view, was creativity and memory as an essential component of reality. ^[23]

Time as "unreal"

In 5th century BC Greece, Antiphon the Sophist, in a fragment preserved from his chief work On Truth held that: "Time is not a reality (hypostasis), but a concept (noêma) or a measure (metron). Greece (Ελλάδα transliterated: Elláda, historically, Ellás,) officially the Hellenic Republic (Ελληνική Δημοκρατία Antiphon the Sophist lived in Athens probably in the last two decades of the 5th century BC " Parmenides went further, maintaining that time, motion, and change were illusions, leading to the paradoxes of his follower Zeno. Parmenides of Elea ( Greek:, early 5th century BC was an Ancient Greek Philosopher born in Elea, a Greek city on the southern coast of Zeno of Elea (ˈziːnoʊ əv ˈɛliə Greek: Ζήνων ὁ Ἐλεάτης (ca ^[24] Time as illusion is also a common theme in Buddhist thought,^[25] and some modern philosophers have carried on with this theme. Buddhism is a family of beliefs and practices J. M. E. McTaggart's 1908 The Unreality of Time, for example, argues that time is unreal (see also The flow of time). John McTaggart Ellis McTaggart ( September 3, 1866 – January 18, 1925) was an Idealist metaphysicist. " The Unreality of Time " is an important paper on the philosophy of time written in 1908 by John McTaggart Ellis McTaggart. Philosophy of space and time is the branch of Philosophy concerned with the issues surrounding the Ontology, Epistemology, and character of Space

However, these arguments often center around what it means for something to be "real". Modern physicists generally consider time to be as "real" as space, though others such as Julian Barbour in his The End of Time argue that quantum equations of the universe take their true form when expressed in the timeless configuration spacerealm containing every possible "Now" or momentary configuration of the universe, which he terms 'platonia'. Julian Barbour (born 1937 is a British physicist with research interests in Quantum gravity. In The End of Time The Next Revolution in Physics, published in 1999 Julian Barbour denies that time exists as anything but an illusion "Configuration space" may also refer to PCI Configuration Space. ^[26] (See also: Eternalism (philosophy of time). Eternalism is a philosophical approach to the ontological nature of time. )

Time in the physical sciences

Main article: Time in physics

From the age of Newton up until Einstein's profound reinterpretation of the physical concepts associated with time and space, time was considered to be "absolute" and to flow "equably" (to use the words of Newton) for all observers. In Physics, the treatment of Time is a central issue It has been treated as a question of Geometry. Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical ^[27] The science of classical mechanics is based on this Newtonian idea of time.

Einstein, in his special theory of relativity,^[28] postulated the constancy and finiteness of the speed of light for all observers. Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial He showed that this postulate, together with a reasonable definition for what it means for two events to be simultaneous, requires that distances appear compressed and time intervals appear lengthened for events associated with objects in motion relative to an inertial observer.

Einstein showed that if time and space is measured using electromagnetic phenomena (like light bouncing between mirrors) then due to the constancy of the speed of light, time and space become mathematically entangled together in a certain way (called Minkowski space) which in turn results in Lorentz transformation and in entanglement of all other important derivative physical quantities (like energy, momentum, mass, force, etc) in a certain 4-vectorial way (see special relativity for more details). Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical In Physics and Mathematics, Minkowski space (or Minkowski spacetime) is the mathematical setting in which Einstein's theory of Special relativity Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another In Physics, the Lorentz transformation converts between two different observers' measurements of space and time where one observer is in constant motion with respect to Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial

Classical mechanics

Newton's Second Law

History of ... Fundamental concepts Space · Time · Mass · Force Energy · Momentum

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Time in classical mechanics

In classical mechanics Newton's concept of "relative, apparent, and common time" can be used in the formulation of a prescription for the synchronization of clocks. Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects Newton's laws of motion are three Physical laws which provide relationships between the Forces acting on a body and the motion of the Early Ideas on Motion The Greek philosophers, and Aristotle in particular were the first to propose that there are abstract principles governing nature Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object In Physics, a force is whatever can cause an object with Mass to Accelerate. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In Classical mechanics, momentum ( pl momenta SI unit kg · m/s, or equivalently N · s) is the product Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects Events seen by two different observers in motion relative to each other produce a mathematical concept of time that works pretty well for describing the everyday phenomena of most people's experience.

Time in modern physics

In the late nineteenth century, physicists encountered problems with the classical understanding of time, in connection with the behavior of electricity and magnetism. Einstein resolved these problems by invoking a method of synchronizing clocks using the constant, finite speed of light as the maximum signal velocity. This led directly to the result that time appears to elapse at different rates relative to different observers in motion relative to one another.

Spacetime

Two-dimensional space depicted in three-dimensional spacetime. SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS The past and future light cones are absolute, the "present" is a relative concept different for observers in relative motion. In Special relativity, a light cone (or null cone) is the pattern describing the temporal evolution of a flash of Light in Minkowski spacetime

Main article: Spacetime

Modern physics views the curvature of spacetime around an object as much a feature of that object as are its mass and volume. SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically

Time has historically been closely related with space, the two together comprising spacetime in Einstein's special relativity and general relativity. Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 According to these theories, the concept of time depends on the spatial reference frame of the observer, and the human perception as well as the measurement by instruments such as clocks are different for observers in relative motion. In Physics, an inertial frame of reference is a Frame of reference which belongs to a set of frames in which Physical laws hold in the same and simplest Even the temporal order of events can change, but the past and future are defined by the backward and forward light cones, which never change. In Special relativity, a light cone (or null cone) is the pattern describing the temporal evolution of a flash of Light in Minkowski spacetime The past is the set of events that can send light signals to the observer, the future the events to which the observer can send light signals. PAST (short for Polska Akcyjna Spółka Telefoniczna, Polish Telephone Joint-stock Company) was a Polish telephone operator in the period between World War I The future is commonly understood to contain all events that have yet to occur All else is non-observable and within that set of events the very time-order differs for different observers.

Time dilation

Main article: Time dilation

"Time is nature's way of keeping everything from happening at once". This article discusses a concept in physics For the concept in sociology see Time displacement. This quote, attributed variously to Einstein, John Archibald Wheeler, and Woody Allen, says that time is what separates cause and effect. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical John Archibald Wheeler ( July 9, 1911 &ndash April 13, 2008) was an eminent American Theoretical physicist. Woody Allen (born Allan Stewart Konigsberg; December 1 1935 is an American Film director, Writer, Actor, Comedian, and Causality describes the relationship between Causes and Effects is fundamental to all natural Science, especially Physics, and has a basis in Einstein showed that people traveling at different speeds, whilst agreeing on cause and effect, will measure different time separations between events and can even observe different chronological orderings between non-causally related events. Though these effects are minute unless one is traveling at a speed close to that of light, the effect becomes pronounced for objects moving at speeds approaching the speed of light. Many subatomic particles exist for only a fixed fraction of a second in a lab relatively at rest, but some that travel close to the speed of light can be measured to travel further and survive much longer than expected (a muon is one example). A subatomic particle is an elementary or composite Particle smaller than an Atom. The muon (from the letter mu (μ--used to represent it is an Elementary particle with negative Electric charge and a spin of 1/2 According to the special theory of relativity, in the high-speed particle's frame of reference, it exists, on the average, for a standard amount of time known as its mean lifetime, and the distance it travels in that time is zero, because its velocity is zero. Special relativity (SR (also known as the special theory of relativity or STR) is the Physical theory of Measurement in Inertial In Physics, an inertial frame of reference is a Frame of reference which belongs to a set of frames in which Physical laws hold in the same and simplest Given an assembly of elements the number of which decreases ultimately to zero the lifetime (also called the mean lifetime) is a certain number that characterizes the rate Relative to a frame of reference at rest, time seems to "slow down" for the particle. Relative to the high-speed particle, distances seems to shorten. Even in Newtonian terms time may be considered the fourth dimension of motion; but Einstein showed how both temporal and spatial dimensions can be altered (or "warped") by high-speed motion.

Einstein (The Meaning of Relativity): "Two events taking place at the points A and B of a system K are simultaneous if they appear at the same instant when observed from the middle point, M, of the interval AB. SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS Time is then defined as the ensemble of the indications of similar clocks, at rest relatively to K, which register the same simultaneously. "

Einstein wrote in his book, Relativity, that simultaneity is also relative, i. e. , two events that appear simultaneous to an observer in a particular inertial reference frame need not be judged as simultaneous by a second observer in a different inertial frame of reference.

Relativistic time versus Newtonian time

Views of spacetime along the world line of a rapidly accelerating observer in a Newtonian universe. In physics the world line of an object is the unique path of that object as it travels through 4- Dimensional Spacetime. The events ("dots") that pass the horizontal line are the events current to the observer.

Views of spacetime along the world line of a rapidly accelerating observer in a relativistic universe. In physics the world line of an object is the unique path of that object as it travels through 4- Dimensional Spacetime. The events ("dots") that pass the two diagonal lines in the bottom half of the image (the past light cone of the observer in the origin) are the events visible to the observer. In Special relativity, a light cone (or null cone) is the pattern describing the temporal evolution of a flash of Light in Minkowski spacetime

The animations on the left and the right visualise the different treatments of time in the Newtonian and the relativistic descriptions. At heart of these differences are the Galilean and Lorentz transformations applicable in the Newtonian and relativistic theories, respectively. The Galilean transformation is used to transform between the coordinates of two Reference frames which differ only by constant relative motion within the constructs of Newtonian In Physics, the Lorentz transformation converts between two different observers' measurements of space and time where one observer is in constant motion with respect to

In both figures, the vertical direction indicates time. The horizontal direction indicates distance (only one spatial dimension is taken into account), and the thick dashed curve is the spacetime trajectory ("world line") of the observer. SpaceTime is a patent-pending three dimensional graphical user interface that allows end users to search their content such as Google Google Images Yahoo! YouTube eBay Amazon and RSS In physics the world line of an object is the unique path of that object as it travels through 4- Dimensional Spacetime. The small dots indicate specific (past and future) events in spacetime.

The slope of the world line (deviation from being vertical) gives the relative velocity to the observer. Note how in both pictures the view of spacetime changes when the observer accelerates.

In the Newtonian description these changes are such that time is absolute: the movements of the observer do not influence whether an event occurs in the 'now' (i. e. whether an event passes the horizontal line through the observer).

However, in the relativistic description the observability of events is absolute: the movements of the observer influences whether an event passes the light cone of the observer. Notice that with the change from a Newtonian to a relativistic description, the concept of absolute time is no longer applicable: events move up-and-down in the figure depending on the acceleration of the observer. The relativity of simultaneity is the concept that simultaneity is not absolute but dependent on the observer

Arrow of time

Main article: Arrow of time

Time appears to have a direction – the past lies behind, fixed and incommutable, while the future lies ahead and is not necessarily fixed. Yet the majority of the laws of physics don't provide this arrow of time. The exceptions include the Second law of thermodynamics, which states that entropy must increase over time (see Entropy); the cosmological arrow of time, which points away from the Big Bang, and the radiative arrow of time, caused by light only traveling forwards in time. The second law of Thermodynamics is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which In Thermodynamics (a branch of Physics) entropy, symbolized by S, is a measure of the unavailability of a system ’s Energy Entropy is the only quantity in the physical sciences that "picks" a particular direction for time sometimes called an Arrow of time. Physical cosmology, as a branch of Astronomy, is the study of the large-scale structure of the Universe and is concerned with fundamental questions about its The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 In particle physics, there is also the weak arrow of time, from CPT symmetry, and also measurement in quantum mechanics (see Measurement in quantum mechanics). Particle physics is a branch of Physics that studies the elementary constituents of Matter and Radiation, and the interactions between them CPT symmetry is a fundamental symmetry of Physical laws under transformations that involve the inversions of charge, parity and Measurement is the process of estimating the magnitude of some attribute of an object such as its length or weight relative to some standard ( unit of measurement) such as Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons The framework of Quantum mechanics requires a careful definition of measurement, and a thorough discussion of its practical and philosophical implications

Quantised time

See also: Chronon

Time quantization is a hypothetical concept. A chronon is a proposed Quantum of time that is a discrete and indivisible "unit" of time as part of a theory that proposes that time is not continuous In the modern established physical theories (the Standard Model of Particles and Interactions and General Relativity) time is not quantized. The Standard Model of Particle physics is a theory that describes three of the four known Fundamental interactions together with the Elementary particles General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916

Planck time (~ 5.4 × 10⁻⁴⁴ seconds) is the unit of time in the system of natural units known as Planck units. In Physics, the Planck time ( tP) is the unit of Time in the system of Natural units known as Planck units. In Physics, the Planck time ( tP) is the unit of Time in the system of Natural units known as Planck units. In Physics, natural units are Physical units of Measurement defined in terms of universal Physical constants, such that some chosen physical Planck units are Units of measurement named after the German physicist Max Planck, who first proposed them in 1899 Current established physical theories are believed to fail at this time scale, and many physicists expect that the Planck time might be the smallest unit of time that could ever be measured, even in principle. Tentative physical theories that describe this time scale exist; see for instance loop quantum gravity. Loop quantum gravity (LQG, also known as loop gravity and Quantum geometry, is a proposed quantum theory of Spacetime which attempts to reconcile the theories

Time and the Big Bang

Stephen Hawking in particular has addressed a connection between time and the Big Bang. Stephen William Hawking CH, CBE, FRS, FRSA (born 8 January 1942 is a British theoretical physicist. The Big Bang is the cosmological model of the Universe that is best supported by all lines of scientific evidence and Observation. He has sometimes stated that we may as well assume that time began with the Big Bang because trying to answer any question about what happened before the Big Bang is trying to answer a question that is meaningless as those events would have been part of a different time frame and different universe outside of the scope of the Big Bang theory. ^[29][30][31]

Aristotelian philosopher Mortimer J. Adler,^[32][33] has criticized some expositions that Hawking has given stating that time didn't exist before the big bang. Mortimer Jerome Adler ( December 28, 1902 &ndash June 28, 2001) was an American Aristotelian philosopher

Hawking, in A Brief History of Time and elsewhere, along with several other modern physicists, has stated his position more clearly and less controversially: that even if time did not begin with the Big Bang and there were another time frame before the Big Bang, no information from events then would be accessible to us, and nothing that happened then would have any effect upon the present time-frame. A Brief History of Time is a Popular science Book written by Stephen Hawking and first published by the Bantam Dell Publishing Group ^[34]

Scientists have come to some agreement on descriptions of events that happened 10⁻³⁵ seconds after the Big Bang, but generally agree that descriptions about what happened before one Planck time (5 × 10⁻⁴⁴ seconds) after the Big Bang will likely remain pure speculation. In Physics, the Planck time ( tP) is the unit of Time in the system of Natural units known as Planck units.

Speculative physics beyond the Big Bang

A graphical representation of the expansion of the universe with the inflationary epoch represented as the dramatic expansion of the metric seen on the left. In the mathematical field of Differential geometry, a metric tensor is a type of function defined on a Manifold (such as a Surface in space Image from WMAP press release, 2006.

While the Big Bang model is well established in cosmology, it is likely to be refined in the future. Little is known about the earliest moments of the universe's history. The Penrose-Hawking singularity theorems require the existence of a singularity at the beginning of cosmic time. The Penrose-Hawking singularity theorems are a set of results in General relativity which attempt to answer the question of whether gravity is necessarily singular However, these theorems assume that general relativity is correct, but general relativity must break down before the universe reaches the Planck temperature, and a correct treatment of quantum gravity may avoid the singularity. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 The Planck temperature, named after German Physicist Max Planck, is the unit of Temperature, denoted by TP in the system of Quantum gravity is the field of Theoretical physics attempting to unify Quantum mechanics, which describes three of the fundamental forces of nature ^[35]

There may also be parts of the universe well beyond what can be observed in principle. If inflation occurred this is likely, for exponential expansion would push large regions of space beyond our observable horizon.

Some proposals, each of which entails untested hypotheses, are:

• models including the Hartle-Hawking boundary condition in which the whole of space-time is finite; the Big Bang does represent the limit of time, but without the need for a singularity. In Theoretical physics, the Hartle-Hawking state, named after James Hartle and Stephen Hawking, is the Wave function of the Universe ^[36]
• brane cosmology models^[37] in which inflation is due to the movement of branes in string theory; the pre-big bang model; the ekpyrotic model, in which the Big Bang is the result of a collision between branes; and the cyclic model, a variant of the ekpyrotic model in which collisions occur periodically. Brane cosmology refers to several theories in Particle physics and cosmology motivated by but not exclusively derived from Superstring theory and String theory is a still-developing scientific approach to Theoretical physics, whose original building blocks are one-dimensional extended objects called strings The ekpyrotic universe, or ekpyrotic scenario, is a cosmological model about the origin and shape of the Universe. Cyclic model refers to several Cosmological models in which the Universe follows infinite self-sustaining cycles (for example an Eternity of Big ^[38][39][40]
• chaotic inflation, in which inflation events start here and there in a random quantum-gravity foam, each leading to a bubble universe expanding from its own big bang. The Chaotic Inflation theory is a variety of the Inflationary universe model which is itself an outgrowth (or extension of the Big bang theory ^[41]

Proposals in the last two categories see the Big Bang as an event in a much larger and older universe, or multiverse, and not the literal beginning. The multiverse (or meta-universe) is the hypothetical set of multiple possible Universes (including our universe that together comprise all of Reality.

Time travel

Main article: Time travel

See also: Time travel in fiction and Grandfather paradox

Time travel is the concept of moving backwards and/or forwards to different points in time, in a manner analogous to moving through space and different than the "normal" flow of time to an earthbound observer. This article details time travel itself For other uses see Time Traveler. Time travel is a common theme in Science fiction and is depicted in a variety of media This article refers to the Time travel paradox In novels based on the television series Doctor Who, "Grandfather Paradox" is the semi-mythical Space is the extent within which Matter is physically extended and objects and Events have positions relative to one another Although time travel has been a plot device in fiction since the 19th century, and one-way travel into the future is arguably possible given the phenomenon of time dilation in the theory of relativity, it is currently unknown whether the laws of physics would allow time travel to the past. A plot device is an element introduced into a story solely to advance or resolve the plot of the story Fiction is the telling of stories which are not real More specifically fiction is an imaginative form of Narrative, one of the four basic Rhetorical modes. This article discusses a concept in physics For the concept in sociology see Time displacement. This page is about the scientific concept of relativity for philosophical or sociological theories about relativity see Relativism. A physical law or scientific law is a Scientific generalization based on empirical Observations of physical behavior (i Any technological device, whether fictional or hypothetical, that is used to achieve time travel is known as a time machine.

A central problem with time travel to the past is the violation of causality; should an effect precede its cause, it would give rise to the possibility of temporal paradox. Causality (but not causation) denotes a necessary relationship between one event (called cause and another event (called effect) which is the direct consequence A temporal paradox is a Paradoxical situation in which a Time traveler causes through actions in the past the exclusion of the possibility of the time travel that Some interpretations of time travel resolve this by accepting the possibility of travel between parallel realities or universes. The multiverse (or meta-universe) is the hypothetical set of multiple possible Universes (including our universe that together comprise all of Reality. The Universe is defined as everything that Physically Exists: the entirety of Space and Time, all forms of Matter, Energy

Perception of time

Time in psychology

See also: Mental chronometry and Sense of time

Even in the presence of timepieces, different individuals may judge an identical length of time to be passing at different rates. Mental chronometry is the use of response time in perceptual-motor tasks to infer the content duration and temporal sequencing of cognitive operations Although the sense of time is not associated with a specific sensory system the work of Psychologists and Neuroscientists indicates that our brains do have a system Commonly, this is referred to as time seeming to "fly" (a period of time seeming to pass faster than possible) or time seeming to "drag" (a period of time seeming to pass slower than possible). The psychologist Jean Piaget called this form of time perception "lived time. Jean Piaget pjaʒɛ ( August 9, 1896 &ndash September 16, 1980) was a Swiss philosopher, natural scientist "

This common experience was used to familiarize the general public to the ideas presented by Einstein's theory of relativity in a 1930 cartoon by Sidney "George" Strube:^[42][43]

Man: Well, it's like this,—supposing I were to sit next to a pretty girl for half an hour it would seem like half a minute,—
Einstein: Braffo! You the idea haf! [sic]
Man: But if I were to sit on a hot stove for two seconds then it would seem like two hours. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical Sic is a Latin word meaning "thus" "so" "as such" or "just as that"

A form of temporal illusion verifiable by experiment is the kappa effect,^[44] whereby time intervals between visual events are perceived as relatively longer or shorter depending on the relative spatial positions of the events. The Kappa effect is a term relating to the human perception of Time. In other words: the perception of temporal intervals appears to be directly affected, in these cases, by the perception of spatial intervals.

Time also appears to pass more quickly as one gets older. Stephen Hawking suggests that the perception of time is a ratio: Unit of Time : Time Lived. Stephen William Hawking CH, CBE, FRS, FRSA (born 8 January 1942 is a British theoretical physicist. For example, one hour to a six-month-old person would be approximately "1:4032", while one hour to a 40-year-old would be "1:349,440". Therefore an hour appears much longer to a young child than to an aged adult, even though the measure of time is the same.

Time in altered states of consciousness

Altered states of consciousness are sometimes characterized by a different estimation of time. Some psychoactive substances – such as entheogens – may also dramatically alter a person's temporal judgement. An entheogen, in the strictest sense is a Psychoactive substance used in a religious or shamanic (or entheogenic) context When viewed under the influence of such substances as LSD, psychedelic mushrooms and peyote, a clock may appear to be a strange reference point and a useless tool for measuring the passage of events as it does not correlate with the user's experience. Lophophora williamsii (loʊˈfɒfərə wɪlˈjæmsiaɪ lō-fof′ŏ-ră will-yăm′sē-ī better known by its common name Peyote, (from the At higher doses, time may appear to slow down, stop, speed up, go backwards and even seem out of sequence. A typical thought might be "I can't believe it's only 8 o'clock, but then again, what does 8 o'clock mean?" As the boundaries for experiencing time are removed, so is its relevance. Many users claim this unbounded timelessness feels like a glimpse into spiritual infinity. To imagine that one exists somewhere "outside" of time is one of the hallmark experiences of a psychedelic voyage. Marijuana, a milder psychedelic, may also distort the perception of time to a lesser degree. Cannabis, also known as marijuana or marihuana, or ganja (from Hindi / Sanskrit: गांजा gānjā hemp) is a ^[45]

The practice of meditation, central to all Buddhist traditions, takes as its goal the reflection of the mind back upon itself, thus altering the subjective experience of time; the so called, 'entering the now', or 'the moment'. Meditation is a mental discipline by which one attempts to get beyond the conditioned "thinking" mind into a deeper state of relaxation or awareness

Culture

Culture is another variable contributing to the perception of time. Anthropologist Benjamin Lee Whorf reported after studying the Hopi cultures that: "… the Hopi language is seen to contain no words, grammatical forms, construction or expressions or that refer directly to what we call “time”, or to past, present, or future…"^[46] Whorf's assertion has been challenged and modified. The Hopi are Native American people who primarily live on the 12635 km² (2531 Pinker debunks Whorf's claims about time in the Hopi language, pointing out that the anthropologist Malotki (1983) has found that the Hopi do have a concept of time very similar to that of other cultures; they have units of time, and a sophisticated calendar. ^[47]

Use of time

See also: Time management and Time discipline

In sociology and anthropology, time discipline is the general name given to social and economic rules, conventions, customs, and expectations governing the measurement of time, the social currency and awareness of time measurements, and people's expectations concerning the observance of these customs by others. In Sociology and Anthropology, time discipline is the general name given to social and economic rules conventions customs and expectations Sociology (from Latin: socius "companion" and the suffix -ology "the study of" from Greek λόγος lógos "knowledge" Anthropology (/ˌænθɹəˈpɒlədʒi/ from Greek grc ἄνθρωπος anthrōpos, "human" -λογία -logia) is the study of In Sociology and Anthropology, time discipline is the general name given to social and economic rules conventions customs and expectations A society is a Population of Humans characterized by patterns of relationships between individuals that share a distinctive Culture and Institutions Economics is the social science that studies the production distribution, and consumption of goods and services.

The use of time is an important issue in understanding human behaviour, education, and travel behaviour. For the Björk song see Human Behaviour Human behavior is the collection of Behaviors exhibited by Human beings and influenced by Education encompasses both the Teaching and Learning of Knowledge, proper conduct, and technical competency Travel behavior is the study of what people do over space, and how people use Transport. Time use research is a developing field of study. Time use research is a developing interdisciplinary field of study dedicated to knowing how people allocate their Time during an average day The question concerns how time is allocated across a number of activities (such as time spent at home, at work, shopping, etc. ). Time use changes with technology, as the television or the Internet created new opportunities to use time in different ways. Technology is a broad concept that deals with a Species ' usage and knowledge of Tools and Crafts and how it affects a species' ability to control and adapt Television ( TV) is a widely used Telecommunication medium for sending ( Broadcasting) and receiving moving Images, either monochromatic The Internet is a global system of interconnected Computer networks However, some aspects of time use are relatively stable over long periods of time, such as the amount of time spent traveling to work, which despite major changes in transport, has been observed to be about 20-30 minutes one-way for a large number of cities over a long period of time. Transport or transportation is the movement of people and goods from one place to another This has led to the disputed time budget hypothesis.

Time management is the organization of tasks or events by first estimating how much time a task will take to be completed, when it must be completed, and then adjusting events that would interfere with its completion so that completion is reached in the appropriate amount of time. Calendars and day planners are common examples of time management tools.

Arlie Russell Hochschild and Norbert Elias have written on the use of time from a sociological perspective. Arlie Russell Hochschild (born 15 January 1940) is a professor of Sociology at the University of California Berkeley. Norbert Elias ( June 22, 1897 &mdash August 1, 1990) was a German sociologist of Jewish descent who later became

See also

Time's mortal aspect is personified in this bronze statue by Charles van der Stappen

See the Time navigation templates below for an exhaustive list of related articles. Charles van der Stappen (Karl Van der Stappen (September 1843 - 1910 Belgian sculptor, was born in Brussels.

Books

• A Brief History of Time
• An Experiment with Time

Organizations

Leading scholarly organizations for researchers on the history and technology of time and timekeeping

• Antiquarian Horological Society - AHS (United Kingdom)
• Association Française des Amateurs d'Horlogerie Ancienne - AFAHA (France)
• Chronometrophilia (Switzerland)
• Deutsche Gesellschaft für Chronometrie - DGC (Germany)
• HORA Associazione Italiana Cultori di Orologeria Antica (Italy)
• National Association of Watch and Clock Collectors - NAWCC (United States of America)

Notes and references

Further reading

• Barbour, Julian (1999). 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 962 - Translatio imperii: Pope John XII crowns Otto I Holy Roman Emperor, the first Holy Roman Emperor Julian Barbour (born 1937 is a British physicist with research interests in Quantum gravity. The End of Time: The Next Revolution in Physics. ISBN 0-19-514592-5.  
• Das, Tushar Kanti (1990). The Time Dimension: An Interdisciplinary Guide. New York: Praeger. ISBN 0275926818.  - Research bibliography
• Davies, Paul (1996). Paul Charles William Davies (born April 22, 1946) is a British-born Physicist, Writer and broadcaster, presently a professor About Time: Einstein's Unfinished Revolution. ISBN 0-684-81822-1.  
• Feynman, Richard [1965] (1994). Richard Phillips Feynman (ˈfaɪnmən May 11 1918 – February 15 1988 was an American Physicist known for the Path integral formulation of quantum The Character of Physical Law. Cambridge (Mass): The MIT Press, 108-126. ISBN 0-262-56003-8.  
• Galison, Peter (1992). Peter Louis Galison is the Pellegrino University Professor in History of Science and Physics at Harvard University. Einstein's Clocks and Poincaré's Maps: Empires of Time. New York: W. W. Norton. ISBN 0-393-02001-0.  
• Highfield, Roger (1992). Arrow of Time: A Voyage through Science to Solve Time's Greatest Mystery. Random House. ISBN 0-449-90723-6.  
• Mermin, N. David (2005). In Solid-state physics, N David Mermin is a polymathic physicist at Cornell University best known for the eponymous Mermin-Wagner theorem and his application It's About Time: Understanding Einstein's Relativity. Princeton University Press. ISBN 0-691-12201-6.  
• Penrose, Roger [1989] (1999). Sir Roger Penrose, PhD, OM, FRS (born 8 August 1931) is an English Mathematical physicist and Emeritus The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics. New York: Oxford University Press, 391-417. ISBN 0-19-286198-0.  
• Price, Huw (1996). Time's Arrow and Archimedes' Point. Oxford University Press. ISBN 0-19-511798-0.  
• Reichenbach, Hans [1956] (1999). Hans Reichenbach ( September 26, 1891 in Hamburg – April 9, 1953 in Los Angeles The Direction of Time. New York: Dover. ISBN 0-486-40926-0.  
• Stiegler, Bernard, Technics and Time, 1: The Fault of Epimetheus
• Whitrow, Gerald J. (1973). Bernard Stiegler (born April 1, 1952) is a French Philosopher and Director of the Department of Cultural Development at the Centre Technics and Time 1 The Fault of Epimetheus ( French: La technique et le temps 1 La faute d'Épiméthée) is a book by the French philosopher Gerald James Whitrow ( June 9 1912, Kimmeridge, Dorset - June 2, 2000) was a British Mathematician, cosmologist The Nature of Time. Holt, Rinehart and Wilson (New York).  
• Whitrow, Gerald J. (1980). The Natural Philosophy of Time. Clarendon Press (Oxford).  
• Whitrow, Gerald J. (1988). Time in History. The evolution of our general awareness of time and temporal perspective. Oxford University Press. ISBN 0-19-285211-6.  
• Rovelli, Carlo (2006). What is time? What is space?. Rome: Di Renzo Editore. ISBN 8883231465.  

External links

Perception of time

• Time and Its Discontents
• Time Perception I and II
• Time Perception Research at the University of Manchester

Physics

• Do we actually measure time?
• A walk through Time
• Time and classical and quantum mechanics: Indeterminacy vs. discontinuity
• Theories With Problems: What Is Time?
• Exploring the Nature of Time
• Myth of the Beginning of Time

Philosophy

Eastern Philosophy

• The Conceptual Scheme of Chinese Philosophical Thinking - Time
• An article on Time and Universal Consciousness

Western Philosophy

• Crouch, Will (2006-2008). Is there a defensible argument for the non-existence of time?. On Philosophy. Retrieved on 2008-01-24. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 41 - Gaius Caesar (Caligula, known for his eccentricity and cruel Despotism, is Assassinated by his disgruntled
• Dowden, Bradley (California State University, Sacramento) (2007). "Time". The Internet Encyclopedia of Philosophy. Ed. James Fieser, Ph. D. , Bradley Dowden, Ph. D. . Retrieved on 2008-01-31. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1504 - France cedes Naples to Aragon. 1606 - Gunpowder Plot: Guy Fawkes  
• Le Poidevin, Robin (Winter 2004). "The Experience and Perception of Time". The Stanford Encyclopedia of Philosophy. Ed. Edward N. Zalta. Retrieved on 2008-01-17. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 38 BC - Octavian marries Livia Drusilla. 1287 - King Alfonso III of Aragon invades Minorca  
• Mcdonough, Jeff (Harvard University) (Winter 2007). "Leibniz's Philosophy of Physics". The Stanford Encyclopedia of Philosophy. Ed. Edward N. Zalta. Stanford University. Retrieved on 2008-01-31. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1504 - France cedes Naples to Aragon. 1606 - Gunpowder Plot: Guy Fawkes  
• Ross, Kelley L. , Ph. D. (Los Angeles Valley College). The Clarke-Leibniz Debate (1715-1716). The Proceedings of the Friesian School, Fourth Series (1996, 1999, 2001). Retrieved on 2008-01-17. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 38 BC - Octavian marries Livia Drusilla. 1287 - King Alfonso III of Aragon invades Minorca
• Ross, Kelley L. , Ph. D. (Los Angeles Valley College). Three Points in Kant's Theory of Space and Time. The Proceedings of the Friesian School, Fourth Series (1996, 1999, 2001). Retrieved on 2008-01-17. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 38 BC - Octavian marries Livia Drusilla. 1287 - King Alfonso III of Aragon invades Minorca
• Savitt, Steven, Ph. D. (University of British Columbia) (Fall 2007). "Being and Becoming in Modern Physics". The Stanford Encyclopedia of Philosophy. Ed. Edward N. Zalta. Retrieved on 2008-01-17. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 38 BC - Octavian marries Livia Drusilla. 1287 - King Alfonso III of Aragon invades Minorca  
• Wilson, Catherine (City University of New York) (Summer 2004). "Kant and Leibniz". The Stanford Encyclopedia of Philosophy. Ed. Edward N. Zalta. Stanford University. Retrieved on 2008-01-31. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1504 - France cedes Naples to Aragon. 1606 - Gunpowder Plot: Guy Fawkes  

Timekeeping

• Different systems of measuring time
• non-SI units
• UTC/TAI Timeserver
• Leapsecond
• Hexadecimal Time
• hexadecimal-time.com
• BBC article on shortest time ever measured
• Interactive World Clock
• Federation of the Swiss Watch Industry FH
• American Watchmakers-Clockmakers Institute
• The World Clock - Time Zones
• World Local Times on Google Map by single click
• World time
• Interactive Map of World Time
• World Time for any place on earth

Miscellaneous

• GMT and all other timezones...
• TimeTicker and the time tickers...
• World Time and Zones
• Official US time
• Exploring Time from Planck Time to the lifespan of the universe
• Time Server Calling to a different time zone; This site can be used to work out what time you should call. Also has some good "history of time" information and information about computer time servers and gps time.

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