A rock is a clock: Physicist uses matter to tell time

Ever since he was a kid growing up in Germany, Holger Müller has been asking himself a fundamental question: What is time?

That question has now led Müller, today an assistant professor of physics at the University of California, Berkeley, to a fundamentally new way of measuring time.

Taking advantage of the fact that, in nature, matter can be both a particle and a wave, he has discovered a way to tell time by counting the oscillations of a matter wave. A matter wave's frequency is 10 billion times higher than that of visible light.

"A rock is a clock, so to speak," Müller said.

In a paper appearing in the Jan. 11 issue of Science, Müller and his UC Berkeley colleagues describe how to tell time using only the matter wave of a cesium atom. He refers to his method as a Compton clock because it is based on the so-called Compton frequency of a matter wave.