Magazine article Science News

New Clock Revolves around Mass: Study Claims That Time Can Be Gauged by an Atom's Heft

Magazine article Science News

New Clock Revolves around Mass: Study Claims That Time Can Be Gauged by an Atom's Heft

Article excerpt

It's part clock, part scale: A newly developed atomic clock measures time based on the mass of a single atom. The research, published online January 10 in Science, is controversial but could provide scientists with more precise methods of measuring both time and mass.

"This is the first clockbased on a single particle," says Holger Muller, a physicist at the University of California, Berkeley. "Its ticking rate is determined only by the particle's mass."

The idea for the clock stemmed from the quantum principle that particles also behave as waves, and vice versa. In particular, Muller and his colleagues wanted to determine how frequently the wave version of a single atom oscillates, a quantity that in quantum mechanics is inherently linked to the atom's mass. Then the researchers could use those oscillations like swings of a pendulum to create a clock.

The snag in that plan was that it's impossible to directly measure the oscillation of waves of matter. The frequency of these waves is about [10.sup.25] hertz, 10 orders of magnitude higher than that of visible light waves. So Muller and his colleagues created two sets of waves--one based on a cesium atom at rest and another on the atom in motion. The researchers measured the frequency difference between the waves and then used that number, a manageable 100,000 hertz or so, to calculate the much larger oscillation frequency of cesium at rest.

With this approach, Muller was able to use the wave frequency of the cesium atom to create a clock that would gain or lose a second every eight years. …

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