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black hole information (non)paradox



By JANE WARDELL, Associated Press Writer

LONDON - 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.

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.

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.