HafeleKeatingeksperimentet

The Hafele–Keating experiment, sometimes referred to as HafeleKeatingeksperimentet in Scandinavian usage, was a 1971 test of time dilation predicted by special and general relativity. Researchers J. C. Hafele and Richard Keating carried atomic clocks on commercial airliners to compare their rates with identical clocks kept on the ground.

Procedure and setup: Four caesium-beam atomic clocks were used. Clocks were flown around the world on two rounds of commercial flights, once eastward and once westward, while identical clocks remained at a reference location on the ground. After each journey, the airborne clocks were compared with the ground clocks to detect any time shifts due to relativistic effects, including velocity time dilation from motion and gravitational time dilation from altitude.

Results: The experiment found small deviations in the airborne clocks relative to the ground reference that were broadly consistent with the predictions of relativity within experimental uncertainties. Specifically, eastbound flights showed a slight loss of time, while westbound flights showed a gain, in a pattern compatible with the combined effects of special and general relativity.

Significance: The Hafele–Keating experiment was among the first direct laboratory-scale confirmations of relativistic time dilation using atomic clocks in motion. While the results were subject to scrutiny regarding systematic errors and environmental factors, they supported the relativistic prediction that moving clocks run slower and that higher altitude clocks run faster relative to clocks at the Earth's surface. The work influenced subsequent precision timekeeping and tests of relativity.