|Managing Editor||Richard Stengel|
|First issue||March 3, 1923|
|Company||Time Inc. (Time Warner)|
Time (trademarked in capitals as TIME) is an American newsmagazine. A European edition (Time Europe, formerly known as Time Atlantic) is published from London. Time Europe covers the Middle East, Africa and, since 2003, Latin America. An Asian edition (Time Asia) is based in Hong Kong. As of 2009, Time no longer publishes a Canadian advertiser edition. The South Pacific edition, covering Australia, New Zealand and the Pacific Islands, is based in Sydney. In some advertising campaigns, the magazine has suggested that, through a backronym, the letters T-I-M-E stand for The International Magazine of Events.
As of mid-2006, Richard Stengel is the managing editor.
Time magazine 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 Henry P. Davison, partner of 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. J.P. Morgan retained a certain control through two directorates and a share of stocks, both over Time and Fortune. Other shareholders were Brown Brothers W. A. Harriman & Co., and The New York Trust Company (Standard Oil).
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 utilizing U.S. radio and movie theaters 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. Jason McManus succeeded Henry Grunwald in 1988 as Editor-in-Chief and oversaw the transition before Norman Pearlstine succeeded him in 1995.
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 is delivered to subscribers on Saturday. The magazine actually began in 1923 with Friday publication.
During early 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.
In 2009, Time announced that they were introducing a personalised print magazine, Mine, mixing content from a range of Time Warner publications based on the reader's preferences. The new magazine met with a poor reception, with criticism that its focus was too broad to be truly personal.
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 digital format.
At the end of 2008, Time discontinued publication of its Canadian edition, which had been in existence for over 60 years.
The distinctive Time writing style was parodied 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, "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".
Time is also known for its signature red border, introduced in 1927 and changed only three times since then. The issue released shortly after the September 11 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.
Time would release another special edition magazine in June 2009 following the death of Michael Jackson. Additionally, the April 28, 2008 issue of Time featured a change from the signature red border: The 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 number 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.
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 for libel. The High Court reversed the judgment of the Appeal Court and Central Jakarta District Court (made in 2000 and 2001). Suharto sought 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.
Time's 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 individuals or even human beings – 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 alleged 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. Corazon Aquino who restored democracy in the Philippines and impressed the U.S. Congress with her speeches is one of four women to grace Time as Woman of the Year.
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 Chávez. Editor Stengel reflected that, if it had been a mistake, "we're only going to make it once."
In 2008, the person of the year was Barack Obama, with Sarah Palin as a runner up. Obama is the twelfth U.S. President (or President-elect) so honored, following a line of every president since Franklin Roosevelt, with the sole exception of Gerald Ford.
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 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.
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.
can be used to keep track of elapsed time. It also concretely represents the present as being between the past and the future.]]
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 it in a non-controversial manner applicable to all fields of study has consistently eluded the greatest scholars.
The Moving Finger writes: and, having writ,
In physics as well as in other sciences, time is considered one of the few fundamental quantities. Time is used to define other quantities – such as velocity – and defining time in terms of such quantities would result in circularity of definition. 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, is highly useful in the conduct of both advanced experiments and everyday affairs of life. 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 spacetime 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.
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. Time travel, in this view, becomes a possibility as other "times" persist like frames of a film strip, spread out across the time line. Sir Isaac Newton subscribed to this realist view, and hence it is sometimes referred to as Newtonian time. 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. This second view, in the tradition of Gottfried Leibniz and Immanuel Kant, holds that time is neither an event nor a thing, and thus is not itself measurable nor can it be travelled.
Temporal measurement has occupied scientists and technologists, and was a prime motivation in navigation and astronomy. 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 in terms of radiation emitted by caesium atoms (see below). 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 life spans.
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. Increasingly, personal electronic devices display both calendars and clocks simultaneously. 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.
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.
in Taganrog (1833)]]
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.
The most precise 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. 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. Great advances in accurate time-keeping were made by Galileo Galilei and especially Christiaan Huygens with the invention of pendulum driven clocks.
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.
|attosecond||1/1018 s||smallest measured time|
|second||SI base unit|
|week||7 days||Also called sennight|
|fortnight||14 days||2 weeks|
|lunar month||27.2–29.5 days||Various definitions of lunar month exist.|
|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||Also called pentad|
|Indiction||15 year cycle|
|jubilee (Biblical)||50 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 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.
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 fraction 1/31,556,925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time.
Time keeping 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). Other scientific time standards include Terrestrial Time and Barycentric Dynamical Time.
Coordinated Universal Time (UTC) is the basis for modern civil time. Since January 1, 1972, it has been defined to follow TAI with an exact offset of an integer number of seconds, changing only when a leap second is added to keep clock time synchronized with the rotation of the Earth. In TAI and UTC systems, the duration of a second is constant, as it is defined by the unchanging transition period of the cesium atom.
Greenwich Mean Time (GMT) is an older standard, adopted starting with British railroads in 1847. Using telescopes instead of atomic clocks, GMT was calibrated to the mean solar time at the Royal Observatory, Greenwich in the UK. Universal Time (UT) is the modern term for the international telescope-based system, adopted to replace "Greenwich Mean Time" in 1928 by the International Astronomical Union. Observations at the Greenwich Observatory itself ceased in 1954, though the location is still used as the basis for the coordinate system. Because the rotational period of Earth is not perfectly constant, the duration of a second would vary if calibrated to a telescope-based standard like GMT or UT - in which a second was defined as a fraction of a day or year. The terms "GMT" and "Greenwich Mean Time" are sometimes used informally to refer to UT or UTC.
The Global Positioning System also broadcasts a very precise time signal worldwide, along with instructions for converting GPS time to UTC.
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 GMT. In many locations these offsets vary twice yearly due to daylight saving time transitions.
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 1/366th of a day (4 minutes) less than a solar day.
Another form of time measurement consists of studying the past. Events in the past can be ordered in a sequence (creating a chronology), and can 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.
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".)
shown logarithmically ]]
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. – Ecclesiastes 3:1–8
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. Christian Science defines time as "error" or illusion.
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 Greek language denotes two distinct principles, Chronos and Kairos. The former refers to numeric, or chronological, time. The latter, literally "the right or opportune moment," relates specifically to metaphysical or Divine time. In theology, Kairos is qualitative, as opposed to quantitative.
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, an approach similar to that taken in other negative definitions.
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 is not shared by Abrahamic faiths as they believe time started by creation, therefore the only thing being infinite is God and everything else, including time, is finite.
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.
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. Kant 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. Spatial measurements are used to quantify the extent of and distances between objects, and temporal measurements are used to quantify the durations of and between events. (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.
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).)
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).
|KeyItems = History of ...
|Topic1 = Fundamental concepts
|Items1 = Space · Time · Mass · Force
Energy · Momentum
|Topic2 = Formulations |Items2 = Newtonian mechanics
|Topic4 = Branches |Items4 = Statics
Statistical mechanics |Topic5 = Scientists |Items5 = Newton · Euler · d'Alembert · Clairaut
Lagrange · Laplace · Hamilton · Poisson
|cTopic=Fundamental concepts }}
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.
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 observers in motion relative to one another will measure different elapsed times for the same event.
. The past and future light cones are absolute, the "present" is a relative concept different for observers in relative motion.]]
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. The past is the set of events that can send light signals to the observer, the future is the set of events to which the observer can send light signals.
before in the blue frame, and will occur later in the red frame.]]
"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 travelling 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 typically minute in the human experience, the effect becomes much more 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 seem 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.
of a rapidly accelerating observer in a relativistic universe. 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.]]
The animations 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 the 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.
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).
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.
Stephen Hawking in particular has addressed a connection between time and the Big Bang. In A Brief History of Time and elsewhere, Hawking says 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. Upon occasion, Hawking has stated that time actually began with the Big Bang, and that questions about what happened before the Big Bang are meaningless. This less-nuanced, but commonly repeated formulation has received criticisms from philosophers such as Aristotelian philosopher Mortimer J. Adler.
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.
with the inflationary epoch represented as the dramatic expansion of the metric seen on the left. 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. 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:
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 is the concept of moving backwards and/or forwards to different points in time, in a manner analogous to moving through space and different from 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.
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 haf zee ideah! [sic]
Man: But if I were to sit on a hot stove for two seconds then it would seem like two hours.
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.
One hour to a six-month-old person would be approximately "1:4368", 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 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. Marijuana, a milder psychedelic, may also distort the perception of time to a lesser degree.
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…"
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.
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We use time to sequence events, to compare their durations and the intervals between them, and to quantify the speed at which objects move and things change.
To measure time, we can use anything that repeats itself regularly. One example is the dawn of a new day (as Earth rotates on its axis). Two more are the phases of the moon (as it orbits the Earth), and the seasons of the year (as the Earth orbits the Sun). Even in ancient times, people developed calendars to keep track of the number of days in a year. They also developed sundials that used the moving shadows cast by the sun through the day to measure times smaller than a day. Today, highly accurate clocks can measure times less than a billionth of a second. The study of time measurement is horology.