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Event

Hafele–Keating experiment

Two atomic clocks are displayed against a backdrop of Earth from space, illustrating the Hafele–Keating experiment to demonstrate relativistic time dilation.

1971 test of relativistic time dilation in which four caesium-beam atomic clocks were flown twice around the Earth on commercial airliners, once eastbound and once westbound, and compared against ground clocks at the U.S. Naval Observatory. The measured offsets matched the combined special- and general-relativistic predictions to within experimental error, providing the first direct macroscopic confirmation of both effects in a single experiment.

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