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Time ⚪｜Definition｜1st｜20251119205401-00-⌔
Time
Time is the continuous progression of existence that occurs in an apparently irreversible succession from the past, through the present, and into the future.123 Time dictates all forms of action, age, and causality, being a component quantity of various measurements used to sequence events, to compare the duration of events (or the intervals between them), and to quantify rates of change of quantities in material reality or in the conscious experience.4567 Time is often referred to as the fourth dimension and the temporal dimension, in addition to the three spatial dimensions.8
Time is primarily measured in linear spans or periods, ordered from shortest to longest. Practical, human-scale measurements of time are performed using clocks and calendars, reflecting a 24-hour day collected into a 365-day year linked to the astronomical motion of the Earth. Scientific measurements of time instead vary from Planck time at the shortest to billions of years at the longest. Measurable time is believed to have effectively begun with the Big Bang 13.8 billion years ago, encompassed by the chronology of the universe. Modern physics understands time to be inextricable from space within the concept of spacetime described by general relativity.9 Time can therefore be dilated by velocity and matter to pass faster or slower for an external observer, though this is considered negligible outside of extreme conditions, namely relativistic speeds or the gravitational pulls of black holes.
Throughout history, time has been an important subject of study in religion, philosophy, and science. Temporal measurement has occupied scientists and technologists, and has been a prime motivation in navigation and astronomy. 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 (“carpe diem”) and in human life spans.
Printed 2026-06-28.
Link to original Footnotes
“Time”. Oxford Dictionaries. Oxford University Press. Archived from the original on 4 July 2012. Retrieved 18 May 2017. The indefinite continued progress of existence and events in the past, present, and future regarded as a whole ↩
“Webster’s New World College Dictionary”. 2010. Archived from the original on 5 August 2011. Retrieved 9 April 2011. 1.indefinite, unlimited duration in which things are considered as happening in the past, present, or future; every moment there has ever been or ever will be… a system of measuring duration 2.the period between two events or during which something exists, happens, or acts; measured or measurable interval “The American Heritage Stedman’s Medical Dictionary”. 2002. Archived from the original on 5 March 2012. Retrieved 9 April 2011. A duration or relation of events expressed in terms of past, present, and future, and measured in units such as minutes, hours, days, months, or years. “Collins Language.com”. HarperCollins. 2011. Archived from the original on 2 October 2011. Retrieved 18 December 2011. 1. The continuous passage of existence in which events pass from a state of potentiality in the future, through the present, to a state of finality in the past. 2. physics a quantity measuring duration, usually with reference to a periodic process such as the rotation of the earth or the frequency of electromagnetic radiation emitted from certain atoms. In classical mechanics, time is absolute in the sense that the time of an event is independent of the observer. According to the theory of relativity it depends on the observer’s frame of reference. Time is considered as a fourth coordinate required, along with three spatial coordinates, to specify an event. “The American Heritage Science Dictionary @dictionary.com”. 2002. Archived from the original on 5 March 2012. Retrieved 9 April 2011. 1. A continuous, measurable quantity in which events occur in a sequence proceeding from the past through the present to the future. 2a. An interval separating two points of this quantity; a duration. 2b. A system or reference frame in which such intervals are measured or such quantities are calculated. “Eric Weisstein’s World of Science”. 2007. Archived from the original on 29 November 2017. Retrieved 9 April 2011. A quantity used to specify the order in which events occurred and measure the amount by which one event preceded or followed another. In special relativity, ct (where c is the speed of light and t is time), plays the role of a fourth dimension. ↩
“Time”. The American Heritage Dictionary of the English Language (Fourth ed.). 2011. Archived from the original on 19 July 2012. A nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future. ↩
“time” (Archived 8 May 2012 at the Wayback Machine) Merriam-Webster Dictionary.com. “the measured or measurable period during which an action, process, or condition exists or continues: duration; a nonspatial continuum which is measured in terms of events that succeed one another from past through present to future”. ↩
Compact Oxford English Dictionary (1971). “A limited stretch or space of continued existence, as the interval between two successive events or acts, or the period through which an action, condition, or state continues”. ↩
“Internet Encyclopedia of Philosophy”. 2010. Archived from the original on 11 April 2011. Retrieved 9 April 2011. Time is what clocks measure. We use time to place events in sequence one after the other, and we use time to compare how long events last… Among philosophers of physics, the most popular short answer to the question ‘What is physical time?’ is that it is not a substance or object but rather a special system of relations among instantaneous events. This working definition is offered by Adolf Grünbaum who applies the contemporary mathematical theory of continuity to physical processes, and he says time is a linear continuum of instants and is a distinguished one-dimensional sub-space of four-dimensional spacetime. “Dictionary.com Unabridged, based on Random House Dictionary”. 2010. Archived from the original on 5 March 2012. Retrieved 9 April 2011. 1. the system of those sequential relations that any event has to any other, as past, present, or future; indefinite and continuous duration regarded as that in which events succeed one another… 3. (sometimes initial capital letter) a system or method of measuring or reckoning the passage of time: mean time; apparent time; Greenwich Time. 4. a limited period or interval, as between two successive events: a long time… 14. a particular or definite point in time, as indicated by a clock: What time is it?… 18. an indefinite, frequently prolonged period or duration in the future: Time will tell if what we have done here today was right. Ivey, Donald G.; Hume, J.N.P. (1974). Physics. Vol. 1. Ronald Press. p. 65. Archived from the original on 14 April 2021. Retrieved 7 May 2020. Our operational definition of time is that time is what clocks measure. ↩
Le Poidevin, Robin (Winter 2004). “The Experience and Perception of Time”. In Edward N. Zalta (ed.). The Stanford Encyclopedia of Philosophy. Archived from the original on 22 October 2013. Retrieved 9 April 2011. ↩
“Newton did for time what the Greek geometers did for space, idealized it into an exactly measurable dimension.” About Time: Einstein’s Unfinished Revolution, Paul Davies, p. 31, Simon & Schuster, 1996, ISBN 978-0-684-81822-1 ↩
Rendall, Alan D. (2008). Partial Differential Equations in General Relativity (illustrated ed.). Oxford University Press. p. 9. ISBN 978-0-19-921540-9. ↩
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