Hafele-Keating Flights Confirmed Time Dilation Within 273 Nanoseconds on 1971 Around-the-World Trips
Updated
Updated · spacedaily.com · Jul 13
Hafele-Keating Flights Confirmed Time Dilation Within 273 Nanoseconds on 1971 Around-the-World Trips
1 articles · Updated · spacedaily.com · Jul 13
Summary
Four caesium-beam atomic clocks flown twice around the world in 1971 returned out of sync with U.S. Naval Observatory clocks by amounts close to Einstein’s predictions, turning ordinary passenger flights into a measurable relativity test.
Eastbound, theory predicted a 40-nanosecond loss and the clocks lost 59; westbound, a 275-nanosecond gain was predicted and 273 was measured, with altitude speeding clocks up and motion slowing them down.
Direction mattered because the relevant speed was relative to a non-rotating Earth: flying east adds to Earth’s rotation and increases time loss, while flying west subtracts from it and lets the clocks gain time.
The same physics is operational in GPS, where satellite clocks run about 38 microseconds a day faster than ground clocks; without relativistic corrections, positioning errors would grow by roughly 10 kilometers daily.
Human 'time travel' remains tiny in practice: long-duration spaceflight has left record-holding cosmonauts only fractions of a second younger than they otherwise would have been.