Feb. 19, 2008 -- Researchers are set to test a new mercury-based clock expected to be the world's most accurate timepiece.
The Tokyo-based research should improve measurements of everything from the speed of light to the strength of electromagnetic forces. It could also improve the accuracy of GPS signals.
"We hope that the proposed clock...will be the most accurate one, although it is not experimentally demonstrated yet," said team leader Hidetoshi Katori, a physicist at the University of Tokyo. The clock will have to run for several weeks before researchers can determine its accuracy.
The study was published recently in Physical Review Letters.
The researchers propose what is called an optical lattice clock, where a set of lasers creates a wave that holds atoms of mercury at rest. Another set of lasers reads the atoms' energy levels to determine the time.
Current clocks are based on the oscillation of the metal cesium, a technology which is more than 50 years old, notes Andrei Derevianko, a professor of physics at the University of Reno and one of the new study's authors. The problem with the cesium clock is that after 30 million years or so, the clock will be off by about one second.
While this might not seem like a big deal, the Global Positioning System (GPS) finds a location based on the very tiny, fractions of a second differences between the signals of orbiting satellites.
Researchers expect the new clock will lose only a fraction of a second over 14 billion years -- that's as long as the universe has existed.
While it will take several weeks to test the new mercury-based clock, the researchers expect it to be more accurate by several magnitudes than other kinds of clocks because it measures millions of atoms simultaneously, instead of a single ion.
In 2005 the researchers reported they had developed a similar clock, made out of strontium. Subsequent tests showed the clock was affected by a certain kind of radiation, known as blackbody radiation. Mercury is not affected by this radiation, so it makes for a more accurate clock.
Mercury is, however, affected by electromagnetism.
In physicists' equations, alpha refers to the strength of the electromagnetic force. For decades it was assumed that the value of alpha was unchangeable. But over the last decade a host of experiments in fields from astronomy to nuclear physics has shown that alpha may have changed.
If scientists find a difference between the alpha-sensitive mercury clock and the alpha-neutral strontium clock, it could usher in a new age of physics.
"Discovery of such variation would lead to a revolution in physics and cosmology," said Victor Flambaum, a physicist at the University of New South Wales in Australia and an expert in alpha measurements. "A new theory will be needed to extend present 'standard model,' including Einstein's general relativity."
But Flambaum cautions that any difference in alpha found by the clock will have to be verified by other experiments. Only time will tell.
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