Paul D. Boyer
America, chemistry

John E. Walker
Britain, chemistry

Jens C. Skou
Denmark, chemistry

Steven Chu
America, physics

William Phillips
France, physics

Claude Cohen-Tannoudji
France, physics

The physics prize went to Americans Steven Chu and William Phillips and Claude Cohen-Tannoudji of France for developing ways of trapping atoms of gas and cooling them to within a millionth of a degree of nature's limit. The discovery has already led to more accurate atomic clocks and a new form of matter whose existence Einstein postulated in the 1920s. "It's wonderful," said Chu, a 49-year-old professor at Stanford University. "I'm delighted to be sharing it with some good friends, and I'm so happy for Stanford."

Chu said the cooling process might someday lead to extremely tiny machines that work on a molecular rather than a mechanical level, such as scrubbers that clear away plaque from arteries or switches in the brain that help people think faster.

Working at Bell Laboratories in 1985, Chu developed a way of trapping thousands of gas atoms using lasers. The atoms are bombarded from six sides by the lasers so that they can't move from a single point. Heat is a product of atomic motion, so the less an atom moves, the colder it is. Chu's laser trapping method can cool atoms to within a thousandth of a degree of absolute zero, the theoretical point where all atomic motion ceases. Absolute zero is -459 degrees Fahrenheit.

In 1987, Phillips, 48, a scientist at the National Institute of Standards and Technology in Gaithersburg, Md., developed a magnetic trapping method that allowed further cooling.

And Cohen-Tannoudji, a 64-year-old professor at the College de France and the Ecole Normale Superieure in Paris, achieved a final level of cooling that can bring atoms to within one-millionth of a degree of absolute zero.

An invention of Chu's based on laser cooling, dubbed the "atomic fountain," can improve the precision of atomic clocks 100 times. Atomic clocks are normally accurate to one second in 32 million years; Chu's improvement makes them accurate to a second in more than 3 billion years. The discovery has also led to the creation of an entirely new form of matter, the Bose-Einstein condensate. Einstein predicted in 1925 that atoms can join at very low temperatures into "superatoms" that all behave as a single particle. Nothing like that had ever existed in the universe until Colorado physicists created the material in their lab two years ago.

It is the second year in a row that the physics prize has gone for work done at temperatures near absolute zero. Last year's prize went to three Americans for discovering that a helium isotope behaves in unusual ways at extremely low temperatures.

This year's Nobel prizes are worth $1 million each. The physics prize will be split equally among the three winners.

In chemistry, Skou, a professor at Denmark's Aarhus University, will receive half for his discovery in 1957 of an enzyme that regulates the concentration of dissolved potassium and sodium inside cells. Boyer, a professor at the University of California at Los Angeles, and Walker, a researcher at the Medical Research Center Council Laboratory of Molecular Biology in England, will share the other half for decades of research on how the energy-storing molecule ATP, or adenosine triphosphate, does its job.

Boyer described ATP as "the currency of the cell." "This is the machine that makes the money that the rest of the body spends. Without it there would be no life at all," he said.