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Temporal measurement

Temporal measurement, or chronometry, takes two distinct period forms: the calendar, a mathematical abstraction for calculating extensive periods of time, and the clock, a concrete mechanism that counts the ongoing passage of time. In day-to-day life, the clock is consulted for periods less than a day, the calendar, for periods longer than a day. The number (as on a clock dial or calendar) that marks the occurrence of a specified event as to hour or date is obtained by counting from a fiducial epoch—a central reference point.

History of the 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 Sumerian civilization of approximately 2000 BC introduced the sexagesimal system based on the number 60. 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. 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. 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.

History of time measurement devices

A large variety of devices have been invented to measure time. The study of these devices is called horology.

An Egyptian device dating to c.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. 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.

A sundial uses a gnomon to cast a shadow on a set of markings which were calibrated to the hour. The position of the shadow marked the hour in local time.

The most accurate timekeeping devices of the ancient world were the water clock or clepsydra, one of which was found in the tomb of Egyptian pharaoh Amenhotep I (1525–1504 BC). 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. Arab inventors and engineers in particular made improvements on the use of water clocks up to the Middle Ages.

The Arab engineers also invented the first mechanical clocks to be driven by weights and gears in the 11th century. Also in the 11th century, the Chinese inventors and engineers invented the first mechanical clocks to be driven by an escapement mechanism.

The hourglass uses the flow of sand to measure the flow of time. They were used in navigation. Ferdinand Magellan used 18 glasses on each ship for his circumnavigation of the globe (1522).

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. Alban's abbey, famously built a mechanical clock as an astronomical orrery about 1330.

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. The passage of the hours at sea were marked by bells, and denoted the time (see ship's bells). The hours were marked by bells in the abbeys as well as at sea.

Clocks can range from watches, to more exotic varieties such as the Clock of the Long Now. 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 chronometer is a portable timekeeper that meets 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. More recently, the term has also been applied to the chronometer watch, a wristwatch that meets precision standards set by the Swiss agency COSC.

The most accurate timekeeping devices are atomic clocks, which are accurate to seconds in many millions of years, and are used to calibrate other clocks and timekeeping instruments. 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. 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.

Definitions and standards

Common units of time
Unit	Size	Notes
picosecond	0.000 000 000 001 seconds	no way of accurately measuring
nanosecond	0.000 000 001 seconds
microsecond	0.000 001 seconds
millisecond	0.001 seconds
second	SI base unit
minute	60 seconds
hour	60 minutes
day	24 hours
week	7 days	Also called sennight
fortnight	14 days	2 weeks
month	28 to 31 days
quarter	3 months
year	12 months
common year	365 days	52 weeks + 1 day
leap year	366 days	52 weeks + 2 days
tropical year	365.24219 days	average
Gregorian year	365.2425 days	average
Olympiad	4 year cycle
lustrum	5 years
decade	10 years
Indiction	15 year cycle
score	20 years
generation	17 - 25 years	approximate
jubilee (Biblical)	50 years
century	100 years
millennium	1,000 years

The SI base unit for time is the SI second. 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. 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 official SI definition of the second is as follows:

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. Previous to 1967, the second was defined as:

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.

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). 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. In many locations these offsets vary twice yearly due to daylight saving time transitions.

Sidereal time

Sidereal time is the measurement of time relative to a distant star (instead of solar time that is relative to the sun). 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

Another form of time measurement consists of studying the past. Events in the past can be ordered in a sequence (creating a chronology), and be put into chronological groups (periodization). 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. Chronology, periodization, and interpretation of the past are together known as the study of history.

Religion and mythology

In the Old Testament book Ecclesiastes, traditionally 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. (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".)

There is an appointed time (zman) for everything. 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.
–

Linear and cyclical 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. 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. 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.

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.

Philosophy

The earliest recorded African philosophy of time was expounded by the ancient Egyptian thinker Ptahhotep (c. 2650–2600 BC), who said: "Do not lessen the time of 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, destruction and rebirth, with each cycle lasting 4,320,000 years. Ancient Greek philosophers, including Parmenides and Heraclitus, wrote essays on the nature of time.

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.

In contrast to ancient Greek philosophers who believed that the universe had an infinite past with no beginning, medieval philosophers and theologians developed the concept of the universe having a finite past with a beginning. This view was inspired by the creation myth shared by the three Abrahamic religions: Judaism, Christianity and Islam. The Christian philosopher, John Philoponus, presented the first such argument against the ancient Greek notion of an infinite past. However, the most sophisticated medieval arguments against an infinite past were developed by the early Muslim philosopher, Al-Kindi (Alkindus); the Jewish philosopher, Saadia Gaon (Saadia ben Joseph); and the Muslim theologian, Al-Ghazali (Algazel). They developed two logical arguments against an infinite past, the first being the "argument from the impossibility of the existence of an actual infinite", which states:

"An actual infinite cannot exist."

"An infinite temporal regress of events is an actual infinite."

"∴ An infinite temporal regress of events cannot exist."

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."

"∴ The temporal series of past events cannot be an actual infinite."

Both arguments were adopted by later Christian philosophers and theologians, and the second argument in particular became more famous after it was adopted by Immanuel Kant in his thesis of the first antimony concerning time.

Isaac Newton believed time and space form a container for events, which is as real as the objects it contains.

In contrast to Newton's belief in absolute space, and a precursor to Kantian time, Leibniz believed that time and space are relational. The differences between Leibniz's and Newton's interpretations came to a head in the famous Leibniz-Clarke Correspondence. 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. 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. 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. Spatial measurements are used to quantify how far apart objects are, and temporal measurements are used to quantify how far apart events occur.

In Existentialism, time is considered fundamental to the question of being, in particular by the philosopher Martin Heidegger. (See Ontology).

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.

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)." Parmenides went further, maintaining that time, motion, and change were illusions, leading to the paradoxes of his follower Zeno. Time as illusion is also a common theme in Buddhist thought, and some modern philosophers have carried on with this theme. J. M. E. McTaggart's 1908 The Unreality of Time, for example, argues that time is unreal (see also The flow of time).

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'. (See also: Eternalism (philosophy of time).)

Physical definition

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. The science of classical mechanics is based on this Newtonian idea of time.

Einstein, in his special theory of relativity, postulated the constancy and finiteness of the speed of light for all observers. 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).

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. 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.

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

Modern physics views the curvature of spacetime around an object as much a feature of that object as are its mass and volume.

Time has historically been closely related with space, the two together comprising spacetime in Einstein's special relativity and general relativity. 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. 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. 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. All else is non-observable and within that set of events the very time-order differs for different observers.

Time dilation

"Time is nature's way of keeping everything from happening at once". This quote, attributed variously to Einstein, John Archibald Wheeler, and Woody Allen, says that time is what separates cause and effect. 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). 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. 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. 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

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.

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. 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 do not influence 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.

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. 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).

Quantised time

Time quantization is a hypothetical concept. In the modern established physical theories (the Standard Model of Particles and Interactions and General Relativity) time is not quantized.

Planck time (~ 5.4 × 10⁻⁴⁴ seconds) is the unit of time in the system of natural units known as Planck units. 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.

Time and the Big Bang

Stephen Hawking in particular has addressed a connection between time and the Big Bang. 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.

Aristotelian philosopher Mortimer J. Adler, has criticized some expositions that Hawking has given stating that time didn't exist before the big bang.

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.

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.

Speculative physics beyond the Big Bang

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. 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.

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.
brane cosmology models 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.
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.

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.

Time travel

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. 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. 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. Some interpretations of time travel resolve this by accepting the possibility of travel between parallel realities or universes.

Theory would point toward there having to be a physical dimension in which one could travel to, where the present (i.e. the point that which you are leaving) would be present at a point fixed in either the past or future. Seeing as this theory would be dependent upon the theory of a multiverse, it is uncertain how or if it would be possible to just prove the possibility of time travel.

Perception of time

Psychology

Even in the presence of timepieces, different individuals may judge an identical length of time to be passing at different rates. 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."

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:

A form of temporal illusion verifiable by experiment is the kappa effect, whereby time intervals between visual events are perceived as relatively longer or shorter depending on the relative spatial positions of the events. 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. 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.

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. 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. 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.

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'.

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… Whorf's assertion has been challenged and modified. 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.

An interesting fact is that in Hindi (offical language of India), there is only one word kal for both yesterday and tomorrow. The Hindi word kal could mean yesterday or it could mean tomorrow, depending on the context.

Use of time

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.

The use of time is an important issue in understanding human behaviour, education, and travel behaviour. Time use research is a developing field of study. 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. 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. 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.

Notes and references

External links

Perception of time

Time Perception Research at the University of Manchester

Physics

A walk through Time

Philosophy

Eastern Philosophy

The Conceptual Scheme of Chinese Philosophical Thinking - Time
An article on Time and Universal ConsciousnessWestern Philosophy
Crouch, Will Is there a defensible argument for the non-existence of time?. On Philosophy. (2006-2008). Retrieved on 2008-01-24..
Time. In The Internet Encyclopedia of Philosophy (2007). Retrieved on 2008-01-31..
The Experience and Perception of Time. In The Stanford Encyclopedia of Philosophy (Winter 2004). Retrieved on 2008-01-17..
Leibniz's Philosophy of Physics. In The Stanford Encyclopedia of Philosophy (Winter 2007). Stanford University. Retrieved on 2008-01-31..
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..
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..
Being and Becoming in Modern Physics. In The Stanford Encyclopedia of Philosophy (Fall 2007). Retrieved on 2008-01-17..
Kant and Leibniz. In The Stanford Encyclopedia of Philosophy (Summer 2004). Stanford University. Retrieved on 2008-01-31..

Timekeeping

Miscellaneous

World Time and Zones
Exploring Time from Planck Time to the lifespan of the universe

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History

Time was created in 1923 by Briton Hadden and Henry Luce, making it the first weekly news magazine in the United States. The two had previously worked together as chairman and managing editor of the Yale Daily News and considered calling the magazine Facts. Hadden was a rather carefree figure, who liked to tease Luce and saw Time as something important but also fun. That accounts for its tone, which many people still criticize as too light for serious news and more suited to its heavy coverage of celebrities (including politicians), the entertainment industry, and pop culture. It set out to tell the news through people, and for many decades the magazine's cover was of a single person. The first issue of Time was published on March 3 1923, featuring on its cover Joseph G. Cannon, the retired Speaker of the United States House of Representatives; a facsimile reprint of Issue No. 1, including all of the articles and advertisements contained in the original, was included with copies of the February 28, 1938 issue as a commemoration of the magazine's 15th anniversary.

On Hadden's death in 1929, Luce became the dominant man at Time and a major figure in the history of 20th-century media.

According to Time Inc.: The Intimate History of a Publishing Enterprise 1972-2004 by Robert Elson, "Roy Edward Larsen […] was to play a role second only to Luce's in the development of Time Inc." In his book, The March of Time, 1935-1951, Raymond Fielding also noted that Larsen was "originally circulation manager and then general manager of Time, later publisher of Life, for many years president of Time, Inc., and in the long history of the corporation the most influential and important figure after Luce."

Around the time they were raising US$100,000 from rich Yale alumni like J.P. Morgan & Co., publicity man Martin Egan and J.P. Morgan & Co. banker Dwight Morrow, Henry Luce and Briton Hadden hired Larsen in 1922 – although Larsen was a Harvard graduate and Luce and Hadden were Yale graduates. After Hadden died in 1929, Larsen purchased 550 shares of Time Inc., using money he obtained from selling RKO stock which he had inherited from his father, who was the head of the B.F. Keith theatre chain in New England. However, after Briton Hadden's death, the largest Time Inc. stockholder was Henry Luce, who ruled the media conglomerate in an autocratic fashion, "at his right hand was Larsen," Time Inc.'s second-largest stockholder, according to "Time Inc.: The Intimate History of a Publishing Enterprise 1923-1941". In 1929, Roy Larsen was also named a Time Inc. director and a Time Inc. vice-president.

By the time of Henry Luce's death in 1967, the Time Inc. stock which Luce owned was worth about US$109 million and yielded him a yearly dividend income of more than US$2.4 million, according to The World of Time Inc: The Intimate History Of A Changing Enterprise 1960-1989 by Curtis Prendergast. The value of the Larsen family's Time Inc. stock was now worth about $80 million during the 1960s and Roy Larsen was both a Time Inc. director and the chairman of its Executive Committee, before serving as Time Inc.'s vice-chairman of the board until the middle of 1979. According to the September 10, 1979 issue of The New York Times, "Mr. Larsen was the only employee in the company's history given an exemption from its policy of mandatory retirement at age 65."

After Time magazine began publishing its weekly issues in March 1923, Roy Larsen was able to increase its circulation by utilising U.S. radio and movie theatres around the world. It often promoted both "Time" magazine and U.S. political and corporate interests. According to The March of Time, as early as 1924, Larsen had brought Time into the infant radio business with the broadcast of a 15-minute sustaining quiz show entitled Pop Question which survived until 1925." Then, according to the same book, "In 1928 […] Larsen undertook the weekly broadcast of a 10-minute programme series of brief news summaries, drawn from current issues of Time magazine […] which was originally broadcast over 33 stations throughout the United States."

Larsen next arranged for a 30-minute radio programme, The March of Time, to be broadcast over CBS, beginning on March 6, 1931. Each week, the programme presented a dramatisation of the week's news for its listeners, thus Time magazine itself was brought "to the attention of millions previously unaware of its existence," according to Time Inc.: The Intimate History Of A Publishing Enterprise 1923-1941, leading to an increased circulation of the magazine during the 1930s. Between 1931 and 1937, Larsen's The March of Time radio programme was broadcast over CBS radio and between 1937 and 1945 it was broadcast over NBC radio – except for the 1939 to 1941 period when it was not aired. People Magazine was based on Time's People page.

Time became part of Time Warner in 1989 when Warner Communications and Time, Inc. merged.

2000s

Since 2000, the magazine has been part of AOL Time Warner, which subsequently reverted to the name Time Warner in 2003.

In 2007, Time moved from a Monday subscription/newsstand delivery to a schedule where the magazine goes on sale Fridays, and Saturday subscription delivery. The magazine actually began in 1923 with Friday publication.

In the beginning of 2007, the year's first issue was delayed for approximately a week due to "editorial changes." The changes included the job losses of 49 employees.

Circulation

In 2007, Time's paid circulation dropped to 3.4 million.

Time Magazine Paid Circulation by Year
Year	1997	1998	1999	2000	2001	2002	2003	2004	2005	2006	2007
Circulation (millions)	4.2	4.1	4.1	4.1	4.1	4.1	4.1	4.0	4.0	4.1	3.4

The magazine has an online archive with the unformatted text for every article published. The articles are indexed and were converted from scanned images using optical character recognition technology. There are still minor errors in the text that are remnants of the conversion into text.

Style

The distinctive Time writing style was parodied most famously in 1936 by Wolcott Gibbs in an article in The New Yorker: "Backward ran sentences until reeled the mind […] Where it all will end, knows God!" The early days of incessantly inverted sentences and "beady-eyed tycoons" and "great and good friends", however, have long since vanished.

Up until the mid-1970s or so, Time had a weekly section called "Listings", which contained capsule summaries and/or reviews of then-current significant films, plays, musicals, television programs, and literary bestsellers, much like The New Yorker's section "Current Events".

As of mid-2008, the magazine continues to follow French spellings for some words, such as élite (with an accent). The magazine has been accused by some of having a liberal bias over the years. With two black and white photographs of Republican Party candidate John McCain and seven color front-page photograph covers of Democratic Party candidate Barack Obama in 2008, the magazine has come under scrutiny by some.

Time is also known for its signature red border, introduced in 1927 and changed only twice since then. The issue released shortly after the September 11, 2001 attacks on the United States featured a black border to symbolize mourning. However, this edition was a special "extra" edition published quickly for the breaking news of the event; the next regularly scheduled issue contained the red border. Additionally, the April 28, 2008 issue of Time featured a change from the signature red border: That 2008 Earth Day issue, dedicated to environmental issues, contained a green border.

In 2007, Time engineered a style overhaul of the magazine. Among other changes, the magazine reduced the red cover border in order to promote featured stories, enlarged column titles, reduced the amount of featured stories, increased white space around articles, and accompanied opinion pieces with photographs of the writers. The changes have met both criticism and praise.

Legal controversy

On September 10, 2007, the Supreme Court of Indonesia awarded former Indonesian President Suharto damages against Time Asia magazine, ordering it to pay him one trillion rupiah ($128.59 million) for libel. The High Court reversed the judgment of the Appeal Court and Central Jakarta District Court (made in 2000 and 2001). Suharto claimed more than US$27 billion ($32bn) in the suit against US-based Time over a 1999 article which published that he transferred stolen money abroad.

Person of the Year

Times most famous feature throughout its history has been the annual "Person of the Year" (formerly "Man of the Year") cover story, in which Time recognizes the individual or group of individuals who have had the biggest effect on the year's news. Despite the title, the recipient is not necessarily an individual – for instance, on January 3, 1983 the personal computer was recognized as "Machine of the Year" (Time.com). In 1989 "Endangered Earth" was named as "Planet Of The Year." In 1999, Albert Einstein was chosen by Time as Person of the Century.

Controversy has occasionally arisen because of the designation of dictators and warmongers as "Persons of the Year". The distinction is supposed to go to the person who, for good or ill, has most affected the course of the year; it is therefore not necessarily an honor or a reward. In the past, such figures as Adolf Hitler and Joseph Stalin have been Man of the Year. In 2001, Time was accused of giving way to political correctness when it named Rudy Giuliani Person of the Year instead of Osama Bin Laden.

In 2006 the Person of the Year was designated as "You", a move that was met with split reviews. Some thought the concept was creative; others wanted an actual person of the year. Others stated, again, that it was due to perceptions of misguided patriotism for many assumed the just bearer of the title to be the President of Venezuela Hugo Chavez. Editor Stengel reflected that, if it had been a mistake, "we're only going to make it once.

The Time 100

In recent years, Time has assembled an annual list of the 100 most influential people of the year. Originally, they had made a list of the 100 most influential people of the 20th century. These issues usually have the front cover filled with pictures of people from the list and devote up a substantial amount of space within the magazine to the 100 articles about each of the people on the list. There have, in some cases, been over 100 people, when two people have made the list together, sharing one spot.

Time For Kids

Written by young reporters, Time For Kids is a division magazine of Time that is especially published for children and is mainly distributed in classrooms. TFK contains some national news, a "Cartoon of the Week", and a variety of articles concerning popular culture. An annual issue concerning the environment is distributed near the end of the U.S. school term. The publication hardly ever reaches above fifteen pages front and back. It is used in many libraries.

Notable contributors

James Agee
Margaret Carlson was the first female columnist for Time.
Whittaker Chambers was editor of Time for a while.
Richard Corliss and Richard Schickel are film critics for the magazine. Schickel has been with the magazine since 1972 while Corliss has been with it since 1980.
Ana Marie Cox writes the Ana Log (a compilation of political tidbits) for the magazine. She is also an acclaimed blogger and author.
Lev Grossman, brother of Bathsheba and Austin, writes primarily about books for the magazine.
Michael Kinsley is a well traveled American journalist and is an essayist for the magazine.
Joe Klein is an author (Primary Colors) and a columnist for the magazine who writes the "In the Arena" column for the magazine.
Nathaniel Lande, author, filmmaker, and former creative director of Time.
Will Lang Jr. 1936–1968, Time Life International
Charles Krauthammer is a commentator for the Washington Post. He also contributes essays to Time.
Robert D. Simon 1950–1987, Time Life International
Joel Stein is a sometimes controversial writer for the magazine who wrote the Joel 100 just after Time Magazine's Most Influential issue in 2006.

References

External links

Time.com - for Breaking News and Analysis (PC & Mac)
Time.mobi - for Breaking News and Analysis (Mobile Phones & PDAs)
Time Archive - Free Archive of all magazines and covers from 1923 through present
Time universe - Time universe on Netvibes
Table of Contents of the Inaugural Issue on March 3, 1923