- For alternate uses of "time", see Time (disambiguation) or see TIME (magazine).
8:17 am, August 6, 1945, Japanese time. This watch was stopped when the nuclear bomb nicknamed the " Little Boy" was detonated over Hiroshima, Japan, near the end of World War II.
Attempting to understand time has long been a prime occupation for philosophers and scientists. There are widely divergent views about its meaning, hence it is difficult to provide an uncontroversial and clear definition of time. This article looks at some of the main philosophical and scientific issues relating to time.
The measurement of time has also occupied scientists and technologists, and was a prime motivation in astronomy. Time is also a matter 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 our lives. Time has long been an important theme for writers, artists and philosophers. Units of time have been agreed upon to quantify the duration of events and the intervals between them. Regularly recurring events and objects with apparently periodic motion have long served as standards for units of time - such as the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum.
Philosophy of time
Main article: Philosophy of space and time; Ontology
In ancient thought, Zeno's paradoxes challenged the conception of infinite divisibility, and eventually led to the development of calculus. Parmenides (of whom Zeno was a follower) believed that time, motion, and change were illusions, basing this on a rather interesting argument. More recently McTaggart held a similar belief.
Newton believed time and space form a container for events, which is as real as the objects it contains. In contrast Leibniz believed that time and space are a conceptual apparatus describing the interrelations between events.
Leibniz and others 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.
The bucket argument proved problematic for Leibniz, and his account fell into disfavour, at least amongst scientists, until the development of Mach's principle. Modern physics views the curvature of spacetime around an object as much a part of that object as are its mass and volume.
Immanuel Kant, in the Critique of Pure Reason, described time as an a priori notion that allows us (together with other a priori notions such as space) to comprehend sense experience. With Kant, neither space nor time are conceived as substances, but rather both are elements of a systematic framework we use to structure our experience. Spatial measurements are used to quantify how far apart objects are, and temporal measurements are used to quantify how far apart events occur.
Nietzsche, inspired by the concept of eternal return in his book Thus Spake Zarathustra, argued that time possesses a circular characteristic. Postulating an infinite past, "all things" must have come to pass therein; the same for an infinite future.
In Existentialism, time is considered fundamental to the question of being, in particular by the philosopher Martin Heidegger.
Time in physics
A tesseract, a cube in 3 dimensions extended to a fourth, as a description of time; adhering to defined finite bounds, all possibilities for this configuration are conceptually representable.
Main article: Time in physics
Prior to Albert Einstein's relativistic physics, time and space had been treated as distinct dimensions; Einstein linked time and space into spacetime. Einstein showed that people traveling at different speeds will measure different times for events and different distances between objects, though these differences are minute unless one is traveling at a speed close to that 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 longer than expected. According to the special theory of relativity, in the high-speed particle's frame of reference, it exists for the same amount of time as usual, and the distance it travels in that time is what would be expected for that velocity. 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.
Measurement
Present day standards
The standard unit for time is the SI second, from which larger units are defined like the minute, hour, and day. Because they do not use the decimal system, and because of the occasional need for a leap-second, the minute, hour, and day are "non-SI" units, but are officially accepted for use with the International System. There are no fixed ratios between seconds (or days) on the one hand and months and years on the other hand -- months and years having significant variations in length. Despite its great social importance, the week is not mentioned even as a "non-SI" unit. (See external pdf file: The International System of Units.)
The measurement of time is so critical to the functioning of our 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 International Atomic Time (TAI). This is the yardstick for other time scales including Coordinated Universal Time (UTC) which is the basis for civil time.
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.
Psychology
Different people may judge identical lengths of time quite differently. Time can "fly"; that is, a long period of time can seem to go by very quickly. Likewise, time can seem to "drag," as in when one performs a boring task.
The judged speed of time depends on a number of factors. If a person has a very long list of tasks to accomplish on a certain day, the day may feel like it has not enough hours to do everything. Likewise, even a short wait at a bus stop while running late can feel endless. A day filled with fun activities can feel very long due to the number of activities that fill it. A long trip can go by quickly if the traveller's mind is occupied.
Time appears to go fast when sleeping, or, to put it differently, time seems not to have passed while asleep. Time also appears to pass more quickly as one gets older. For example, a day for a child seems to last longer than a day for an adult. One convincing reason for this is simple. With increasing age, each segment of time is an increasingly smaller percentage of the person's total experience.
Adult humans and other animals may perceive time to pass more quickly because it provides the evolutionary advantage of bestowing more patience upon adults, so they are better at long term planning, which benefits the community.
Altered states of consciousness are sometimes characterised by a different estimation of time. Some psychoactive substances--such as entheogens--may also dramatically alter a person's temporal judgement.
Use of time
The use of time is an important issue in understanding human behaviour, education, and travel behaviour. 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.
Arlie Russell Hochschild and Norbert Elias have written on the subject from a sociological perspective.
Quotations
Wikiquote has a collection of quotations by or about:
"Time is an illusion, lunchtime doubly so." - Douglas Adams, The Hitchhiker's Guide to the Galaxy
"What is time? If nobody asks me, I know; but if I were desirous to explain it to one that should ask me, plainly I know not." - Augustine of Hippo
"Time is what keeps the light from reaching us." - Meister Eckhart
"Life holds one great but quite commonplace mystery. Though shared by each of us and known to all, seldom rates a second thought. That mystery, which most of us take for granted and never think twice about, is time." - Michael Ende
"Time is the accident of accidents." - Epicurus
"Truth is always new, therefore timeless." - J. Krishnamurti
"I confess I do not believe in time." - Vladimir Nabokov
"We are not capable of producing a concept of time that is at once cosmological, biological, historical and individual." - Paul Ricoeur
"Nature's Time is Cubic and perpetual. Linear Time is wrong and suicidal." - Gene Ray
This thing all things devours:
Birds, beasts, trees, flowers;
Gnaws iron, bites steel,
Grinds hard stones to meal;
Slays king, ruins town,
And beats high mountain down.
- - Riddle about time by J. R. R. Tolkien, The Hobbit
"Time is what prevents everything from happening at once. Space is what prevents everything from happening to me." - attributed to John Archibald Wheeler
"Time reflexes like a whore/falls wanking to the floor." - David Bowie "Time"
"How can I tell that the past isn't a fiction designed to account for the discrepancy between my immediate physical sensations and my state of mind?" - Douglas Adams, The Restaurant at the End of the Universe (by the man in the shack)
"Time is the school in which we learn, Time is the fire in which we burn." Delmore Schwartz (1913-1966) from "For Rhoda" [1938]
"Remember that time is money." Benjamin Franklin 'Advice to a Young Tradesman', [1748]
"Time is the effect of existence and the measure of our world." - Mark F. Herron
See also
General units of time
Special units of time
Light-year is the distance light can travel in an Earth year and so is a unit of distance rather than time.
Time measurement and horology
Theory and study of time
External links
Perception of time
Physics
Timekeeping
Miscellaneous
Further reading
- Hightfield, Roger (1992). Arrow of Time: A Voyage through Science to Solve Time's Greatest Mystery. Random House. ISBN 0449907236.
- Peter Galison, Einstein's Clocks and Poincaré's Maps: Empires of Time (2003).
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