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I think it's fairly well known that Einstein made an incorrect prediction in his 1905 paper on special relativity. "Thence we conclude that a spring-clock at the equator must go more slowly, by a very small amount, than a precisely similar clock situated at one of the poles under otherwise identical conditions." Once he developed GR, it became clear that there would be zero effect from latitude, because the Earth's surface is an equipotential.
What I hadn't realized was that there was a direct empirical test of this done in the 1970's by Alley et al. A description of the experiment is online here: http://www.pttimeeting.org/archivemeetings/index9.html Alley's group flew atomic clocks from Washington, DC to Thule, Greenland, left them there for four days, and brought them back. The difference between the clocks that went to Greenland and other clocks that stayed in Washington was 38+-5 ns, which was consistent with the 35+-2 ns effect predicted purely based on kinematic and gravitational time dilation while the planes were in the air. If Einstein's 1905 prediction had been correct, then there would have been an additional difference of 224 ns due to the difference in latitude.
What I hadn't realized was that there was a direct empirical test of this done in the 1970's by Alley et al. A description of the experiment is online here: http://www.pttimeeting.org/archivemeetings/index9.html Alley's group flew atomic clocks from Washington, DC to Thule, Greenland, left them there for four days, and brought them back. The difference between the clocks that went to Greenland and other clocks that stayed in Washington was 38+-5 ns, which was consistent with the 35+-2 ns effect predicted purely based on kinematic and gravitational time dilation while the planes were in the air. If Einstein's 1905 prediction had been correct, then there would have been an additional difference of 224 ns due to the difference in latitude.
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