January 11, 2013
Berkeley Physicist Uses Atomic Matter To Tell Time
Brett Smith for redOrbit.com - Your Universe Online
In a groundbreaking new study, physicists from the University of California, Berkeley have used atomic matter to measure time.
According to a new report in the journal Science, Holger MÃ¼ller and his Berkeley colleagues describe how to tell time using a cesium atom and the theory that matter can be both a particle and a wave.
"When you make a grandfather clock, there is a pendulum and a clockwork that counts the pendulum oscillations,” MÃ¼ller explained in a Berkeley statement. “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."
However, MÃ¼ller realized he could measure the oscillations by combining two well-known physics techniques to create such a clockwork.
First, it should be noted that, in relativity, time slows down for moving objects. To explain this theory, physicists describe the so-called twin paradox that says if a twin flies off to a distant star and returns–he or she will be younger than the twin who stayed behind. Similarly, a cesium atom that vibrates away and returns is younger than an atom that stands still. Therefore, the moving cesium matter wave will have oscillated fewer times.
In the lab, MÃ¼ller created an atomic pendulum by bouncing photons from a laser off the cesium atoms, causing them to move. Using an optical frequency comb and an atom interferometer as his clockwork, he was able to calculate the difference in frequency between the waves of the fixed atoms and the ones in motion.
"Our clock is accurate to within 7 parts per billion," he said. "That's like measuring one second out of eight years, about as good as the very first cesium atomic clock about 60 years ago.”
MÃ¼ller also flipped this finding on its head–proposing to use time to measure mass. A new mass standard would be welcomed by the international General Conference on Weights and Measures, which currently uses a platinum-iridium cylinder to define one kilogram. MÃ¼ller said this new standard would be derived from an incredibly pure crystal of silicon, dubbed an Avogadro sphere, which is precisely manufactured to the atom.
"Our clock and the current best Avogadro spheres would make one of the best realizations of the newly defined kilogram," he said. "Knowing the ticking rate of our clock is equivalent to knowing the mass of the particle, and once the mass of one atom is known, the masses of others can be related to it."
MÃ¼ller said his study´s findings are an extension of his lifelong quest to understand the very nature of time.
"When I was very young and reading science books, I always wondered why there was so little explanation of what time is," he said. “´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."