Astrophysicist Stephen Hawking
Hawking will present his findings at the 17th International Conference on General Relativity and Gravitation in Dublin, Ireland on July 21.
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updated 7/16/2004 4:47:46 PM ET 2004-07-16T20:47:46

After almost 30 years of arguing that a black hole swallows up everything that falls into it, astrophysicist Stephen Hawking backpedaled Thursday. In doing so, he lost one of the most famous bets in recent scientific history.

The world-famous author of a "Brief History of Time" said he and other scientists had gotten it wrong —the galactic traps may in fact allow information to escape.

"I've been thinking about this problem for the last 30 years, and I think I now have the answer to it," Hawking told the British Broadcasting Corp.'s "Newsnight" program.

"A black hole only appears to form but later opens up and releases information about what fell inside. So we can be sure of the past and predict the future."

The findings, which Hawking is due to present at the 17th International Conference on General Relativity and Gravitation in Dublin, Ireland, on July 21, could help solve the "black hole information paradox," which is a crucial puzzle of modern physics.

A puzzle of modern physics
Exactly what happens in a black hole, a region in space where matter is compressed to such an extent that not even light can escape from its immense gravitational pull, has long puzzled scientists.

Black holes occur when a massive star burns up its nuclear fuel and gravity forces it to collapse in on itself, and the enormous weight of the star's outer layers implodes its core. The crushing force of gravity prohibits nearly all light from escaping and nothing inside can be glimpsed from the outside.

The star virtually disappears from the universe into a point of infinite density, a place where the laws of general relativity that govern space and time break down.

Hawking has devoted most of his life to studying these questions.

Initially, cosmologists believed the holes were like a cosmic vacuum cleaner, sucking up everything in their path.

Hawking revolutionized the study of the holes when he demonstrated in 1976 that, under the strange rules of quantum physics, once black holes form they start to "evaporate" away, radiating energy and losing mass in the process.

Under this theory, black holes are not totally "black" because the vacuum of the imploding star lets out very tiny amounts of matter and energy in the form of photons, neutrinos and other subparticles.

By conjuring up this so-called "Hawking radiation," the Cambridge mathematician, who is paralyzed by amyotrophic lateral sclerosis, also created one of the biggest conundrums in physics.

These particles, he said, contained no information about what has been occurring inside the black hole, or how it formed. Under his theory, once the black hole evaporates, all the information within would be lost.

New theory
But now, according to his latest revision, Hawking argues that eventually some of the information about the black hole can be determined from what it emits.

The information has important philosophical and practical consequences.

"We can never be sure of the past or predict the future precisely," he said. "A lot of people wanted to believe that information escaped from black holes but they didn't know how it could get out."

Hawking did not elaborate on the BBC program how the information could be extracted from the black hole.

Curt Cutler, from the Albert Einstein Institute in Golm, Germany, which is chairing the meeting in Dublin, told New Scientist magazine that Hawking asked at the last minute for permission to address the conference.

"He sent a note saying `I have solved the black hole information paradox and I want to talk about it,'" Cutler said.

If Hawking succeeds in making his case, he will lose a bet that he and theoretical physicist Kip Thorne of the California Institute of Technology made with John Preskill, also of Caltech.

The terms of the bet were that "information swallowed by a black hole is forever hidden and can never be revealed."

Preskill bet against that theory.

The forfeit is an encyclopedia, from which Preskill can recover information at will.

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