Coldest spot in the universe is in physicists' lab

July 14, 1995|By Los Angeles Times

In a discovery that experts are calling "breathtaking" and "beautiful" -- and of "Nobel Prize caliber" -- physicists at the University of Colorado at Boulder have created an entirely new state of matter. It exists only in the coldest spot in the universe, currently a carrot-sized tube in the laboratory of physicists Carl Weiman and Eric Cornell.

Albert Einstein predicted more than 70 years ago that atoms chilled to sufficiently frigid temperatures should "freeze" into this new state, just as liquid water freezes into solid ice. More compact even than a solid, the new state of matter contains several thousand atoms all merged into one.

"What's unbelievable is that it happened just the way we hoped it would," Dr. Weiman said. "It's downright magical."

Dan Kleppner at the Massachusetts Institute of Technology, who has also been working for years to achieve the super-cold state, said the Colorado experiment was "clear and convincing, good enough for a textbook, although obviously we would have loved to [do] it first."

Experiments on the new matter will give physicists a deeper understanding of how atoms behave when all the residual quivering motion of heat is taken away and atoms sing out pure tones, undistorted by the static noise that normally pervades the universe.

Although no practical applications are foreseen for the immediate future, a clearer understanding of atomic behavior has always led to startling advances -- including lasers, computers, medical diagnostics and materials. The experiment is described in today's issue of Science.

Einstein and Indian physicist Satyendra Nath Bose speculated that atoms of matter could condense into a single "superatom" at sufficiently cold temperatures. Called the Bose-Einstein condensate after its founders, this new state of matter can exist only at a whisper above absolute zero -- the ideal but unreachable limit to cold, where no motion exists apart from the innate restlessness of subatomic particles.

The cluster of atoms in Dr. Weiman's tube registered just 170-billionth of a degree above absolute zero -- the coldest temperature in the universe.

Drs. Weiman and Cornell produced their record cold by combining several approaches used by different groups -- including Dr. Kleppner's. First, they slowed rubidium atoms by bombarding them from all sides with laser beams. (Cold, in the atomic world, means slow.) Then they turned on a magnetic trap, and allowed the faster (hotter) atoms to evaporate, just as the fastest (hottest) molecules escape first from a cup of coffee. What was left was the most sluggish atomic brew in creation.

These super-chilled atoms then went through a kind of alchemy, transforming from hard matterlike particles into compressible particles like light. A major challenge was figuring out how to see the super-cold atoms, because any light shined on them would destroy the condensate.

The researchers solved this problem by shining a flash of laser light so short that it acts like a strobe, snapping the picture before the atoms have time to disperse. "It blows the condensate away," said Dr. Cornell, "but the flash is so short we can still take the picture."

The new state does not form at once, but freezes rather gradually at first, like water freezing in an ice tray. Once it starts, says Dr. Cornell, "it's a runaway process."

The glob of condensed atoms stays in the trap for about 20 seconds before flying apart as room-temperature atoms -- which are a trillion times hotter -- leak in. The new matter appears as a bright glow in the center of a diffuse cloud -- just like freezing water.

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