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Fact-Checking Relativity

July 31, 2013

Newsflash: The laws of physics remain in effect! For now, anyway.

That’s according to a team of Berkeley physicists who decided to peek under the hood of the universe and double-check that everything is still chugging along as expected. Namely, the researchers wanted to see if the speed of light, posited by one Albert Einstein to be the unbreakable speed limit for all things always and everywhere, is maybe a little flexible as upper-limit after all.

According to Einstein’s special theory of relativity, light, whether it’s travelling from an object at rest or being emitted from an interstellar spaceship traveling at science-fictional speeds, will always maintain a steady pace of some 186,000 miles per second. That is the speed of light—and, pointedly, nothing else. Every other moving particle in the universe, including electrons, will never outstrip that unassailable constant.

Michael Hohensee, a post-doctoral researcher within Berkeley’s Department of Physics, wanted to test that proposition. There is, after all, a discrepancy between Einstein’s view of the physical world and the Standard Model, the reigning theory that explains how reality operates at the subatomic level.

And so, along with graduate student Nathan Leefer, professor Dmitry Budker, and physicists from the University of New South Wales in Sydney, Hohensee decided to see whether the maximum speed of an electron whizzing around an atom might vary depending on which direction it’s traveling. If the speed of the electron was found to fluctuate with the rotation of the earth or with the gravitational pull of the sun, special relativity could be called into question—and more esoteric phenomena explained by different versions of string theory could be explained.

For the test, Hohensee turned to the rare earth, dysprosium. The electrons that cluster around this element’s nucleus can be nudged, without all that much energy, from a low-energy state to a much a higher, faster one, with a microwave beam. If, for example, it turned out that the energy needed to “kick” an electron from the slow lane into the fast lane varied, that would imply that the maximum speed was changing—slowing down below and inching up over the so-called constant of the speed of light.

But after routine 12-hour tests conducted regularly over the course of two years, no such variation was detected. Within 17 nanometers per second (an unprecedented degree of precision in measurement), the maximum speed of an electron did not budge. Special relativity is still looking strong, though an even more accurate repeat of the experiment is already in the works.

For the layperson, it’s a bit hard to know what to make of all this. Even if an electron were found overtaking the speed of light, what would that mean exactly?

According to Hohensee, a whole lot for the field of physics.

“That would be very exciting!” he told me over the phone. “It would be like, ‘Here’s something that we thought we understood and it turns out we don’t.’”

That kind of finding and the data that would emerge from it would also help physicists sort through competing theories that currently try to reconcile Einstein’s general relativity and the subatomic Standard Model.

But putting aside those convulsions within the halls of academia, what about the day-to-day implications? How quickly would the discovery of faster-than-light particles translate into Star Trek–worthy technology for those of us who can’t understand the math?

“Actually, even if an electron was found to go slightly faster than the speed of light, the difference would be so small that it wouldn’t have a major impact on how we do things,” explained Hohensee. “It wouldn’t be useful in sending messages faster than the speed of light or traveling to distant stars.”

Despite further questioning along these lines, Hohensee remained as stubbornly resolute as the speed of light.

“No, sorry,” he said with the patience that only a physicist speaking to a journalist with a B.A. could summon. “Time travel won’t be happening either.”

—Ben Christopher

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