Testing Einstein's Ultimate Speed Limit: Searching for Particles Faster than Light

There's nothing faster than the speed of light--or is there? Albert Einstein's assertion that this ultimate speed limit exists may be called into question. Researchers are checking whether some particles break this law, which would overturn a theory that has withstood countless tests over the past 100 years.

"As a physicist, I want to know how the world works, and right now our best models of how the world works--the Standard Model of particle physics and Einstein's theory of general relativity--don't fit together at high energies," said Michael Hohensee of the University of California, Brekeley, in a news release. "By finding points of breakage in the models, we can start to improve these theories."

In order to test the theory of relativity, the researchers used a new technique involving two isotopes of the element dysprosium. My measuring the energy required to change the velocity of electrons as they jumped from one atomic orbital to another while Earth rotated over a 12-hour period, the scientists determined that the maximum speed of an electron--in theory, the speed of light--is the same in all directions to within 17 nanometers per second. These measurements were 10 times more precise than previous attempts to measure the maximum speed of electrons.

That's not all the researchers found, though. Using the two isotopes of dysprosium as "clocks," the scientists also showed that as the Earth moved closer to or farther from the sun over the course of two years, the relative frequency of these "clocks" remained constant. That confirms what Einstein predicted in his general theory of relativity.

Needless to say, the scientists didn't disprove any theories with these experiments. Yet they're planning on continuing to push the theory's limits with further experiments.  In addition, the new method they used could also pave the way for future discoveries.

"This technique will open up the door to studying a whole other set of parameters that could be even more interesting and important," said Dmitry Budker, one of the researchers, in a news release.

The findings are published in the journal Physical Review Letters.