Leggett, meanwhile, applied ideas about superconductivity to explain how atoms behave in one kind of "superfluid" in the 1970s. His theory has proven useful for other fields of physics, like the study of particles and of the universe, the Swedish academy said.

Superfluidity occurs when liquid helium is chilled to near absolute zero, the coldest anything can get. The liquid begins to flow freely with little apparent friction. It can even climb up the sides of a beaker.

Phil Schewe, a physicist and chief science writer at the American Institute of Physics, said superfluidity doesn't appear to have as many applications as superconductivity. But "it may well prove to be important just because it is so odd," he said.

The Swedish academy said researchers can use superfluid helium to study other physical phenomena, like how order can turn to chaos. Such research might illuminate the ways in which turbulence arises, "one of the last unsolved problems of classical physics," the Swedish academy said.

A Japanese and two American astrophysicists won last year's prize for using some of the most obscure particles and waves in nature to increase understanding of the universe.

Riccardo Giacconi, 71, of the Associated Universities Inc. in Washington, D.C., was cited for his role in "pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources."

Raymond Davis Jr., 87, of the University of Pennsylvania and Japanese scientist Masatoshi Koshiba, 76, of the University of Tokyo, were awarded for their construction of giant underground chambers to detect neutrinos, elusive particles that stream from the sun by the billion.

This year's Nobel awards started last week with the awarding of the Nobel literature prize to South Africa author J.M. Coetzee.

On Monday, American Paul C. Lauterbur, 74, and Briton Sir Peter Mansfield, 70, were selected by a committee at the Karolinska Institute for the 2003 Nobel Prize for medicine for discoveries leading to development of the MRI body-scanning technique.

The winner of the Nobel Prize in chemistry will be named on Wednesday morning and the Bank of Sweden Prize in Economic Sciences in Memory of Alfred Nobel later the same day.

The winner of the coveted peace prize — the only one not awarded in Sweden — will be announced Friday in Oslo, Norway.

Alfred Nobel, the wealthy Swedish industrialist and inventor of dynamite who endowed the prizes, left only vague guidelines for the selection committees.

In his will he said the physics prize should be given to those who "shall have conferred the greatest benefit on mankind" and "shall have made the most important discovery or invention within the field of physics."

The academy, which also chooses the chemistry and economics winners, invited nominations from previous recipients and experts in the fields before cutting down its choices.

The prizes, which include a gold medal and a diploma, are presented on Dec. 10, the anniversary of Nobel's death in 1896, in Stockholm and in Oslo, Norway.

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On the Net: Nobel Foundation: http://www.nobel.se