Relativistic Time at the US Naval Observatory

Matsakis, Demetrios

A brief and almost equationless review of timing in relativity, including the Principle of Least Action and a heuristic explanation of why time is responsible for an apple wanting to leave its tree so as to fall into a curved space, will be followed in increasing detail by a description of the Hafele-Keating experiment, Peil et al.ís use of atomic fountains to test local position invariance and the constancy of the fundamental constants, and on-going experiments using GPS and Two Way Satellite Time Transfer to test the Principle of Equivalence. A discussion of the issues involving the interpretation of the lack of a noon-midnight frequency shift in GPS will be included. This shift is a possible frequency difference that might be expected to occur because clocks are known to run slower in a stronger gravitational field, and the clocks are closer to the Sun at noon than at midnight.

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