Historical photos and information about the Hafele-Keating experiment

Ben Crowell

I teach physics, and I love the Hafele-Keating experiment as a way to introduce relativity. Because the experiment has a lot of charisma, it's cool to be able to show students photos of the men and the clocks aboard the plane. I've obtained and scanned copies some of these and posted them here. Below each low-resolution photo is a link to a full-resolution version.

In the course of digging up the photos, I ended up compiling some other links and information. Below the photos I've presented some of these items that might be of historical or pedagogical interest.

Photos

Hafele and Keating with clocks

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This photo is from Time Magazine, October 18, 1971, where it appeared with "AP" written above the upper right corner. It may be copyrighted by the Associated Press, or it may have been taken by someone else and now be in the public domain. In the event that it is still copyrighted, it is reproduced here under the fair use exception to U.S. copyright law. Article (paywalled). I have retouched the photo, but that retouching is not copyrightable under U.S. law.

An online listing of errata for early editions of the textbook by Hartle says that the photo (below) of Luther and Dabney had been published with an erroneous caption describing them as Hafele and Keating. Hartle says, "A correct picture of Hafele and Keating [the one shown above] on their initial flight is below. Thanks to Robert Nelson of the Satellite Engineering Research Corporation for pointing out this error and supplying the correct picture." It is therefore possible that the photo was taken by Nelson, or it may be that Nelson simply supplied Hartle with a copy.

Hafele and Keating with clocks and stewardess

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From Popular Mechanics, January 1972, p. 30. Article in Google Books. I don't know the copyright status of this photo. This issue of Popular Mechanics does not give specific photo credits for almost any of the photos in it. If this was a snapshot taken by the crew or another passenger, then it is now in the public domain due to its publication without notice before 1977. If it was taken by a photographer as a work for hire, then it is (c) 1971 Hearst Corporation. If it was taken by an employee of the U.S. Naval Observatory, then it is a public-domain product of the U.S. government. In the event that it is copyrighted, I am reproducing it here under the fair use exception to U.S. copyright law. I have retouched the photo, but that retouching is not copyrightable under U.S. law.

Luther and Dabney boarding plane

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This photo, from the same era as the Hafele-Keating experiment, shows U.S. Naval Observatory technicians George Luther and Bill Dabney boarding a commercial plane with an atomic clock. It is a public-domain product of the U.S. government.

Navy plane and clock used for Alley's Chesapeake Bay experiment

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These photos show a plane and set of atomic clocks used in a 1975-6 experiment by Alley et al., which was basically a higher-precision repeat of the Hafele-Keating experiment. Inside the sealed box are three Cs clocks and three Rb clocks. The plane's motion was measured accurately by radar so that the kinematic time dilation could be eliminated. A pulsed laser system was used in order to get a real-time comparison of the flying clocks with an identical set on the ground, thereby measuring the gravitational time dilation at the plane's 9000 m elevation. I'm guessing that the top photo might be public domain, since the plane is a Navy plane. I don't know the copyright status of the bottom one.

Other contemporary accounts in the popular press

Scientific papers describing the Hafele-Keating experiment

Papers by Alley et al.

A group at the University of Maryland led by C. Alley did clock-on-plane experiments similar to Hafele and Keating's, improving the precision and measuring the relativistic effects to about 1% and testing the dependence on variables such as latitude.

Other scientific papers of historical or pedagogical interest

Modern hobbyist Tom Van Baak has done a truly amazing mountain-valley experiment of this flavor with a second-hand atomic clock in the family minivan. There is a web site and mailing list (Time Nuts) for people who do high-precision timing experiments for fun, and they have a museum with old photos and documentation.

I would be grateful to anyone who could e-mail me with any of the following: