SCIENCE FORUM

Ultimate Precision
Atoms and lasers -- inside the clocks of the future
American physicists have created a clock so accurate it will not have gained or lost a second 200 million years from now -- good news for the most punctual among us though we may not be around to test the claim.
The secret to making an extremely accurate clock is making it tick faster.
"If you make a mistake, you can know about that mistake very fast," said Jun Ye, who developed the atomic clock at the Joint Institute for Laboratory Astrophysics.
Ye's clock has 430 trillion "ticks" per second!
Its pendulum uses thousands of strontium atoms suspended in grids of laser light. This allows the resear-chers to trap the atoms and measure the movement of energy inside.
"Essentially, we are probing the energy structure of the atom. We are probing how electrons make transitions between a set of energy levels," Ye said.
"This is the time scale that was made by the universe. It is very stable."
The clock outperforms the current official atomic clock used by the US's National Institute of Standards and Technology (NIST), reports Science magazine. The latter is thought to remain accurate down to the second for 80 million years.
"These clocks are improving so rapidly that it is impossible to tell which one will be the best," said Tom O'Brian, head of the Time and Frequency Division at NIST.
In case you were wondering, such high precision clocks are critical for deep space navigation, where even the most minute errors can make or break a space mission.
To test his clock's accuracy, Ye and colleagues compared it with another optical atomic clock -- this one measuring calcium atoms. This calcium clock is highly stable only over short periods of time, so the researchers had to make fast measurements for their comparisons.
Next Ye wants to take on a clock that measures a single ion, or charged particle, of mercury. This clock, also developed at JILA, was accurate to about 1 second in 400 million years in 2006. Because Ye's clock measures thousands of atoms at once, it produces stronger signals, something Ye thinks may give him an edge.
"These clocks are among the best in the world," says John Lowe, leader of the atomic standards group at NIST. "Longer-term experiments will prove which of these clocks may end up becoming the next standard of international agreement."
Ye said pushing for ever more accurate clocks will allow physicists to test some of the basic questions about the nature of the universe.

Science Forum is compiled and edited by Rashida Ahmad.
Sources: Nature,New Scientist, Scienc

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Live slow, die young

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