MessageToEagle.com - A physics professor at the University of California, Berkeley, Holger Müller, has
found a 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.
Post-doc Shau-Yu Lan, graduate student Pei-Chen Kuan and assistant professor Holger Muller
with some of their experimental apparatus for creating a Compton clock. Image courtesy of Damon English, UC Berkeley.
"When I was very young and reading science books, I always wondered why there was so little explanation of what time is."
"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."
Müller and his UC Berkeley colleagues describe how to tell time using only the matter wave of a cesium atom and refer to
the method as a Compton clock because it is based on the so-called Compton frequency of a matter wave.
Müller's Compton clock is still 100 million times less precise than today's best atomic clocks, which employ aluminum ions,
but improvements in the technique could boost its precision to that of atomic clocks, including the cesium clocks now used
to define the second, according to Müller.
Two years ago, he found a way to use matter waves to confirm Einstein's gravitational redshift - that is, that time slows
down in a gravitational field and he built an atom interferometer that treats atoms as waves and measures their interference.
"At that time, I thought that this very, very specialized application of matter waves as clocks was it," Müller said.
"When you make a grandfather clock, there is a pendulum and a clockwork that counts the pendulum oscillations. So you
need something that swings and a clockwork to make a clock. There was no way to make a clockwork for matter waves, because
their oscillation frequency is 10 billion times higher than even the oscillations of visible light."
Last year, Müller decided to combine two well-known techniques to create such a clockwork and explicitly demonstrate that
the Compton frequency of a single particle is, in fact, useful as a reference for a clock.
In relativity, time slows down for moving objects, so that a twin who flies off to a distant star and returns will be
younger than the twin who stayed behind.
This is the so-called twin paradox.
Quantum mechanically, mass can be used to measure time and vice versa.
Similarly, a cesium atom that moves away and then returns is younger than one that stands still. As a result, the moving
cesium matter wave will have oscillated fewer times.
The difference frequency would be around 100,000 fewer oscillations per second out of 10 million billion billion
oscillations (3 x 1025 for a cesium atom), might be measurable.
Müller could measure this difference by allowing the matter waves of the fixed and moving cesium atoms to interfere
in an atom interferometer. The motion was caused by bouncing photons from a laser off the cesium atoms.
Using an optical frequency comb, he synchronized the laser beam in the interferometer with the difference frequency between
the matter waves so that all frequencies were referenced solely to the matter wave itself.
And what about the question: What is time?
"I don't think that anyone will ever have a final answer, but we know a bit more about its properties. Time is physical as
soon as there is one massive particle, but it definitely is something that doesn't require more than one massive particle
for its existence. We know that a massless particle, like a photon, is not sufficient," Holger Müller says.
Müller hopes to push his technique to even smaller particles, such as electrons or even positrons, in the latter
case creating an antimatter clock.
He is hopeful that someday he'll be able to tell time using quantum fluctuations in a vacuum.
The paper was published in the Jan. 11 issue of the journal Science