Around-the-World Atomic Clocks: Observed Relativistic Time Gains

Area of Science:

• Physics
• Experimental Physics

Background:

• The Hafele-Keating experiment tested Einstein's theory of relativity.
• Previous tests involved smaller, less precise instruments.

Purpose of the Study:

• To empirically test relativistic time dilation using macroscopic cesium beam atomic clocks.
• To resolve the macroscopic clock paradox with real-world experimental data.

Main Methods:

• Four cesium beam atomic clocks were flown on commercial jetliners.
• Flights were conducted eastward and westward around the globe in October 1971.
• Clock time differences were compared to the U.S. Naval Observatory's atomic time scale.

Main Results:

• Eastward-flying clocks lost 59 ± 10 nanoseconds.
• Westward-flying clocks gained 273 ± 7 nanoseconds.
• Observed time differences closely matched predictions from conventional relativity theory.

Conclusions:

• The experiment provided unambiguous empirical resolution of the macroscopic clock paradox.
• Results validate the predictions of special and general relativity regarding time dilation.