Sat, Nov 20, 2004 - Page 7 News List

British scientists build world's most accurate clock

THE GUARDIAN , LONDON

Scientists in London have announced the creation of the world's most accurate clock.

The development will not only provide improved precision in the Global Positioning System (GPS) and navigation for deep-space probes, it could also redefine time itself -- by changing the way the second is measured -- and allow scientists to study the most fundamental questions in physics.

The accurate definition of time is important for everything from the movement of information over the Internet to distributing electricity, and billions of dollars of financial transactions.

The second is currently defined using atomic clocks, invented in 1955. By detecting and measuring the absorption of microwaves by atoms of caesium, scientists at the UK's National Physical Laboratory (NPL) in Teddington pro-duced a clock that was accurate to one part in 10 billion. In 1967, the clock became the basis for the definition of the second as the duration of 9,192,631,770 cycles of the radiation corresponding to the transition between two atomic states of the caesium atom.

By 2000, the best atomic clocks were so accurate they only lost one ten-billionth of a second a day. But scientists weren't satisfied, said Patrick Gill, a scientist who developed the new clock.

"The problem with that approach is that we're running into the buffers in terms of how much better we can make it," he said.

"It's partly due to the fact that we're using a microwave frequency. People have long postulated that you'd be better off making a time standard with something of a higher frequency -- basically it's ticking quicker," he said.

"We count the frequency of atomic transitions like the ticking of a clock," Gill said. "The more ticks we can count in a given period of time, the more accurately we can measure time."

Gill's new clock uses a single strontium ion and is three times more accurate than the American optical clock. The results of his research are published yesterday in the journal Science.

"The most significant technology application is in navigation and global positioning," Gill said. "At the moment, you have a constellation of satellites with microwave clocks in them and they're referenced to master clocks on the ground. With that arrangement, we can determine position to about several meters."

If the NPL's clock is accepted as the new method for defining a second -- and it may take some years -- it could also provide a tool for analysing the most fundamental laws of physics.

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