Physics @ Berkeley
Physics in the News
Title: A Rock Is A Clock
URL: http://newscenter.berkeley.edu/2013/01/10/a-rock-is-a-clock-physicist-
uses-matter-to-tell-time/
Date: 01/10/2013
Publication: Berkeley News Center
Editor: Robert Sanders
Extended Text:

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.

“When I was very young and reading science books, I always wondered why there was so little explanation of what time is,” said Müller, who is also a guest scientist at Lawrence Berkeley National Laboratory. “Since then, I’ve often asked myself, ‘What is the simplest thing that can measure time, the simplest system that feels the passage of time?’ Now we have an upper limit: one single massive particle is enough.”

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