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Hafele-Keating Experiment Celebrating Its 50th Anniversary

Hafele and Keating inside a passenger airplane with large pieces of equipment
Ben Crowell
/
lightandmatter.com
Hafele and Keating inside a passenger airplane with large pieces of equipment

This year marks the 50th anniversary of the Hafele-Keating experiment, a test of Einstein's theory of general relativity. Joseph Hafele, the physicist that worked on the experiment, is a former Laramie resident.

The Hafele-Keating experiment took four atomic clocks aboard commercial airliners. They flew twice around the world, first eastward, then westward, and compared the clocks against others that remained at the U.S. Naval Observatory.

Dr. Michael Pierce, an associate professor in the Department of Physics & Astronomy at the University of Wyoming, said "the effect that was predicted was, both clocks, regardless of what direction they moved, experienced the general relativistic effect of time moving faster, the further you get away from the earth's gravitational field."

This was viewed as a confirmation of Einstein's prediction. While you might wonder why this matters, Pierce said it's simple - if you have any sort of GPS system, you owe a debt of gratitude to Einstein's theory of relativity and to the Hafele-Keating experiment that made GPS possible.

"Because in order to determine our precise location on earth, what one does is compare signals that are generated by the GPS satellite system. So, all of those calculations by Einstein, go into calculating your position on the earth," Pierce explained.

So whenever you pull out your phone and read your current location, then you can appreciate these effects that were verified experimentally by Hafele-Keating 50 years ago.

Alan Moore, a retired professor in applied Statistics at UW, was Hafele's personal friend. He said that he had the privilege of hearing the stories of the experiment from Joe Hafele himself, some of which were amusing.

"Some of the stories were about having difficulties with customs, people not quite understanding what they were doing with these big machines in the seats of the airplanes, and how skeptical some people were. Just hearing the excitement he described what that was like was fun for me," Moore said.

Angie Varca, Hafele's third out of four daughters, said she was aware of what he did. But to her, he was just Dad.

"He was working really hard to try to support a family of six. He was busy, but a very good father. I would say, a loving and a strict father. He liked to share his ideas with us… talked about science with us at the dinner table," Varca said.

After losing his tenure at the University of Washington to another professor working on moon rocks, Hafele worked at Caterpillar, a machinery company, in the research department.

"For my father who felt like maybe it wasn't recognized in its time, I don't think he really kind of reached a place of peace and self-satisfaction, until he retired and moved to Laramie," Varca mentioned.

Varca said her Dad never left science, even in retirement.

Varca added, "even after he retired, he always did experiments, he was always running experiments, and continuing to write papers and he really had a very amazing mind. And sometimes I ask myself, how would he have dealt with what's going on right now. I think he would have seen it as a challenge in a problem."

She admitted that she is very proud of his accomplishments.

"If it were to come up in conversation, especially with anybody who is a physicist, or has studied physics, they may not know my father's name, but they know his experiment. They know about the experiment that flew atomic clocks around the world to delve into the idea of Einstein's general relativity. And it's kind of satisfying to be able to say 'that was my dad who did that,'" Varca said.

Experts say the Hafele-Keating experiment is a timeless finding, giving us ideas about time, and GPS location. It is one of the most important experiments in the 20th century.

The official 50th anniversary is in October.

This story is supported by a grant through Wyoming EPSCoR and the National Science Foundation.

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