Instant

In physics and the philosophy of science, instant refers to an infinitesimal interval in time, whose passage is instantaneous. In ordinary speech, an instant has been defined as "a point or very short space of time," a notion deriving from its etymological source, the Latin verb instare, from in- + stare ('to stand'), meaning 'to stand upon or near.'^[1]

The continuous nature of time and its infinite divisibility was addressed by Aristotle in his Physics, where he wrote on Zeno's paradoxes. The philosopher and mathematician Bertrand Russell was still seeking to define the exact nature of an instant thousands of years later.^[2]

As of October 2020^[update], the smallest time interval certified in regulated measurements is on the order of 397 zeptoseconds (397 × 10⁻²¹ seconds).^[3]

In correspondence

In correspondence, particularly before the twentieth century, instant (usually abbreviated to inst.) can be used to indicate "of the current month". For example, "the 11th inst." means the 11th day of the current month.^[4]^[5] Its use is consistent with the Latin proximo (prox.) for the following month, and ultimo (ult.) for the month just past.^[6]

References

^ Webster's New World College Dictionary, 4th ed. (1999), p. 740.
^ W. Newton-Smith (1984), "The Russellian construction of instants", The structure of time, Routledge, p. 129, ISBN 978-0-7102-0389-2
^ "Zeptoseconds: New state record in short time measurement". Science Daily. 2020-10-16. Retrieved 2010-05-12.
^ "instant". oxfordreference.com. Oxford University Press. Retrieved 2024-07-05.
^ Chambers, Alfred B. (1900). The New Century Standard Letter-Writer. Chicago: Laird & Lee. p. 258.
^ Crowther, Mary Owens (1922). How to Write Letters. New York: Garden City Publishing Co. p. 41.

Time

Key concepts

Measurement
and standards

Chronometry	UTC Universal Time TAI Unit of time Orders of magnitude (time)
Measurement systems	Italian six-hour clock Thai six-hour clock 12-hour clock 24-hour clock Relative hour Daylight saving time Chinese Decimal Hexadecimal Hindu Jain Metric Roman Sidereal Solar Time zone
Calendars	Main types Solar Lunar Lunisolar Gregorian Julian Hebrew Islamic Solar Hijri Chinese Hindu Panchang Maya List
Clocks	Main types astronomical astrarium atomic quantum hourglass marine sundial watch 24-hour wristwatch mechanical stopwatch water-based Cuckoo clock Digital clock Grandfather clock History Timeline

Philosophy of time

Human experience
and use of time

Time in science

Geology	Geological time age chron eon epoch era period Geochronology Geological history of Earth
Physics	Absolute space and time Arrow of time Chronon Coordinate time Instant Proper time Spacetime Theory of relativity Time domain Time translation symmetry Time reversal symmetry
Other fields	Chronological dating Chronobiology Circadian rhythms Clock reaction Glottochronology Time geography

v t e Time measurement and standards
International standards	Coordinated Universal Time offset UT ΔT DUT1 International Earth Rotation and Reference Systems Service ISO 31-1 ISO 8601 International Atomic Time 12-hour clock 24-hour clock Barycentric Coordinate Time Barycentric Dynamical Time Civil time Daylight saving time Geocentric Coordinate Time International Date Line IERS Reference Meridian Leap second Solar time Terrestrial Time Time zone 180th meridian
Obsolete standards	Ephemeris time Greenwich Mean Time Prime meridian
Time in physics	Absolute space and time Spacetime Chronon Coordinate time Discrete time and continuous time Proper time Theory of relativity Time dilation Gravitational time dilation Time domain Time-translation symmetry T-symmetry
Chronometry	Clock Astrarium Atomic clock Complication History of timekeeping devices Hourglass Marine chronometer Marine sandglass Radio clock Watch stopwatch Water clock Sundial Dialing scales Equation of time History of sundials Sundial markup schema
Calendar	Gregorian Hebrew Hindu Holocene Islamic (lunar Hijri) Julian Solar Hijri Astronomical Dominical letter Epact Equinox Intercalation Julian day Leap year Lunar Lunisolar Solar Solstice Tropical year Weekday determination Weekday names
Archaeology and geology	Chronological dating Geologic time scale International Commission on Stratigraphy
Astronomical chronology	Galactic year Nuclear timescale Precession Sidereal time
Other units of time	Instant Flick Shake Jiffy Second Minute Moment Hour Day Week Fortnight Month Year Olympiad Lustrum Decade Century Saeculum Millennium
Related topics	Orders of magnitude Chronology Duration music Mental chronometry Decimal time Metric time System time Time value of money Timekeeper

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Instant

In correspondence

See also

References

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