Tests of special and general relativity

In 1971, scientists tested both parts of Einstein’s theory by placing precisely synchronized atomic clocks in airliners and flying them around the world. A check of the timepieces after the planes landed showed that the clocks aboard the airliners were running a tiny bit slower than (less than one millionth of a second) than the clocks on the ground.

The disparity resulted from the speed of the planes (a special relativity effect) and their greater distance from the center of Earth’s gravitational field (a general relativity effect).