Time
Forces and Motion

The flight of ‘Mr Clocks’

Stories from Physics for 11-14 14-16 IOP RESOURCES

One of the best-known tests of the time dilation prediction of Einstein’s theory of relativity was the Hafele-Keating experiment. Hafele and Keating flew twice round the world on commercial flights (once eastward and once westward) with fourcaesium beam atomic clocks and compared the time on the flown clocks with others that had remained stationary. The project was relatively cheap for cutting edge research, requiring the purchase of eight round-the-world tickets for $7,600. The atomic clocks travelled under the assumed name of ‘Mr Clocks’ and required two adjacent seats due to their size. When the airborne clocks were compared with the stationary ones, the differences in the time readings were consistent with the predictions of Einstein’s theory of relativity.

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