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Telling the time, with ultra-accuracy

New technology is making precise atomic clocks even better than earlier, for a range of functions

NEW YORK: Some physicists are creating a revolution in the arcane world of ultra-precise clocks. And among them is a researcher who has trouble getting anywhere on time.

"I do tend to be a little bit late," said Jim Bergquist, 58. "Quite a bit late."

Of course, the time he focusses on professionally is far removed from the world of dinner dates and planes to catch. Mr. Bergquist, who is with the National Institute of Standards and Technology in Boulder, Colorado, works with extremely accurate devices that rely on the behaviour of atoms to measure time. In fact, he is working on what could be the world's most accurate such timepiece.

In Mr. Bergquist's world, a 10-billionth of a second is just too long a time between ticks of a clock. And it really makes a difference that a clock in 1,600-metre-high Denver ticks faster than another at sea level. (Time itself passes more quickly when gravity is reduced.)

In his line of work, the focus is not on producing the highly accurate clocks that report the official time of the world. It is on producing the even-more-precise devices that are used to judge the accuracy of those clocks.

Such devices are also used to sharpen interplanetary navigation. Ultimately, they should also help reveal fundamental secrets of the universe, and perhaps help in sending secure information over the Internet.

Mr. Bergquist and others have demonstrated a better way to make them, an approach he figures will eventually replace the technology that has reigned for 50 years. The new way is so accurate that Mr. Bergquist believes it will probably make scientists redefine just what a second is.

This summer, Mr. Bergquist and colleagues published a head-to-head comparison of the U.S.' standard ultra-precise clock with the new technology he and others have been pursuing. The results were pretty clear.

The current standard clock will neither gain nor lose a second in 70 million years. The new clock pushes that figure out to 400 million years.

Mr. Bergquist figures that with further development, the new technology will become 100 times as accurate as the standard kind of clock could ever be.

The secret of the new clock? It "ticks" faster than the standard one. And the more ticks per unit of time, the more precisely that unit can be measured.

Think of trying to time a 100-m dash: If your clock ticks only once a second, Mr. Bergquist said, it will be hard to determine the winner if the race comes down to a hundredth of a second. But a stopwatch that ticks every one-thousandth of a second will do the job.

In fact, Mr. Bergquist's device is more like a stopwatch than a clock. It is turned on only intermittently to measure particular intervals of time, rather than being left on continuously to reveal the time of day.

The new clock technology may not only displace the old, but it may also force a revision in what physicists regard as the definition of one second. The current definition, like the ultra-precise clocks now in use, is based on microwaves and the behaviour of a cesium atom.

The nucleus of a cesium atom switches back and forth between two physical states when it is hit with microwave radiation of a particular frequency. That frequency is the "tick" of current clocks. One second, to physicists, is 9,192,631,770 such ticks.

AP

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