Time

:For alternate uses of "time", see Time (disambiguation) or see TIME (magazine).

Time in physics

Main article: Time in physics

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Time is currently one of few fundamental quantities (quantities which cannot be defined via other quantities because there is nothing more fundamental known at present). Thus, similar to definition of other fundamental quantities (like space and mass) time is defined via measurement. Currently standard time interval (called conventional second, or simply second) is defined as 9 192 631 770 oscillations of specified transition in Cs-133 atom.

Related Topics:
Fundamental - Space - Mass - Measurement

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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.

Related Topics:
Albert Einstein - Spacetime - Subatomic particle - Special theory of relativity - Frame of reference - Velocity

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Einstein (The Meaning Of Relativity - 1968): "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.

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Related Topics:
Mass - Energy - Block time - Free will - Causality - Eternity

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