International Atomic Time ( TAI, from the French name temps atomique international) is a high- precision atomic coordinate time standard based on the notional passage of proper time on Earth' s geoid. It is the principal realisation of Terrestrial Time ( with a fixed offset of is also the basis for Coordinated Universal Time ( UTC), which is used for civil timekeeping all over the Earth' s.
According to the theory of relativity, time dilation is a difference in the elapsed time measured by two observers, either due to a velocity difference relative to each other, or by being differently situated relative to a gravitational field. As a result of the nature of spacetime, a clock that is moving relative to an observer will be measured to tick slower than a clock that is at rest in.
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