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Definition of TIME DILATION
: a slowing of time in accordance with the theory of relativity that occurs in a system in motion relative to an outside observer and that becomes apparent especially as the speed of the system approaches that of light —called also time dilatation
First Known Use of TIME DILATION
In the theory of special relativity, the slowing down of a clock as perceived by an observer in relative motion with respect to that clock. Time dilation becomes noticeable only at speeds approaching that of light and has been accurately confirmed by the apparent increased lifetime of unstable subatomic particles traveling at nearly the speed of light and by the precise timing of atomic clocks carried on airplanes. See alsoLorentz-FitzGerald contraction.