Editing Hafele–Keating experiment (section)

{{Short description|Test of relativistic time dilation}}
[[File:Hafele–Keating experiment.jpg|thumb|right|Hafele and Keating aboard a commercial airliner, with two of the atomic clocks]]
[[File:HP 5061A Cesium Beam Frequency Standard.JPG|thumb|right|One of the actual HP 5061A Cesium Beam atomic clock units used in the Hafele–Keating experiment]]
 
The '''Hafele–Keating experiment''' was a test of the [[theory of relativity]]. In 1971,<ref>The flights were completed October 7. ({{cite web|work=[[The New York Times]] |date= October 8, 1971|url= https://www.nytimes.com/1971/10/08/archives/they-beat-the-clock-checking-on-einstein.html |title=They beat the clock checking on Einstein| access-date=2020-05-03}})</ref> [[Joseph C. Hafele]], a physicist, and [[Richard E. Keating]], an astronomer, took four [[cesium]]-beam [[atomic clock]]s aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks in motion to stationary clocks at the [[United States Naval Observatory]]. When reunited, the three sets of clocks were found to disagree with one another, and their differences were consistent with the predictions of [[special relativity|special]] and [[general relativity]].