Part of the thinking behind Einstein's Theories of Relativity is what it would be like to ride a beam of light. Eventually the mathematics of such a trip showed that the speed of light should be the maximum speed of the Universe, but in some situations, relativity breaks down. Researchers at the University of California, Berkeley and the University of New South Wales have recently made some of the most accurate speed measurements in one of these situations.
The Theories of Relativity do a good job of describing large objects, but small particles are still dominated by the Standard Model, and these theories do not play nicely together at high energies. To test the speed limit proposed by relativity, the researchers turned to isotopes of dysprosium. They then measured the speed at which electrons move from one atomic orbital to another and found it does not exceed the speed of light. The researchers also found that the electrons' speeds were the same in all directions, within 17 nanometers per second, which is ten times more precise than previous measurements.
One of the impressive aspects of this research is how simple the setup was, compared to the massive particle accelerators that could perform comparable studies. Eventually it may be improved to be a thousand times more sensitive, and reach the point where some believe relativity will break down.