[Paleopsych] NYT: About Those Fearsome Black Holes? Never Mind
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About Those Fearsome Black Holes? Never Mind
NYT July 22, 2004
By DENNIS OVERBYE
Dr. Stephen W. Hawking threw in the towel yesterday, or at
least an encyclopedia.
Dr. Hawking, the celebrated Cambridge University
cosmologist and best-selling author, declared at a
scientific conference in Dublin that he had been wrong in a
controversial assertion he made 30 years ago about black
holes, the fearsome gravitational abysses that can swallow
matter and energy, even light.
As atonement he presented Dr. John Preskill, a physicist
from the California Institute of Technology, with a
baseball encyclopedia.
The encyclopedia was the stake in a famous bet Dr. Hawking
and another Caltech physicist, Dr. Kip Thorne, made with
Dr. Preskill in 1997. Dr. Hawking and Dr. Thorne said
information about what had been swallowed by a black hole
could never be retrieved from it; Dr. Preskill and many
other physicists said it could. The winner was to get an
encyclopedia, from which information could be freely
retrieved.
This esoteric sounding debate is of great consequence to
science, because if Dr. Hawking had been right, it would
have violated a basic tenet of modern physics: that it is
always possible to reverse time, run the proverbial film
backward and reconstruct what happened in, say, the
collision of two cars or the collapse of a dead star into a
black hole.
Now, on the basis of a new calculation, Dr. Hawking has
concluded that physics is safe and information can escape
from a black hole. "I want to report that I think that I
have solved a major problem in theoretical physics," he
told his colleagues, according to a transcript of his
remarks.
Standing in front of television cameras, as well as an
auditorium full of physicists, Dr. Preskill said he had
always dreamed that there would be witnesses when Dr.
Hawking conceded, but "this really exceeds my
expectations," according to an account by The Associated
Press.
Dr. Hawking's new calculation was received by other
physicists with reserve. They cautioned that it would take
time to understand it. Some of them emphasized that a long
line of work by various theorists in recent years suggested
that information could escape from black holes.
"Until Stephen's recent reversal, he was about the only
person still getting it wrong," said Dr. Leonard Susskind,
a theorist at Stanford.
Dr. Hawking spoke yesterday at the 17th International
Conference of General Relativity and Gravitation. He was
added to the program at the last minute, only two weeks
ago, after sending a note to the organizers that he had
solved the problem.
His dramatic timing seems sure to add to his legend. Dr.
Hawking, 62, has been confined to a wheelchair for decades
by amyotrophic lateral sclerosis, or Lou Gehrig's disease,
and speaks through a voice synthesizer hooked to a computer
on which he types one letter at a time.
Nevertheless, he has been one of the world's leading
experts on gravity, traveling the world constantly,
training generations of graduate students at Cambridge and
writing books like the popular "Brief History of Time." He
has also married twice and fathered three children, and
appeared on "The Simpsons" and "Star Trek: The Next
Generation."
Theorists have worried about the fate of information in
black holes since the 1960's. In 1974, Dr. Hawking stunned
the world by showing that when the paradoxical quantum laws
that describe subatomic behavior were taken into account,
black holes should leak and eventually explode in a shower
of particles and radiation.
The work was, and remains, hailed as a breakthrough in
understanding the connection between gravity and quantum
mechanics, the large and the small in the universe.
But there was a hitch, as Dr. Hawking pointed out. The
radiation coming out of the black hole would be random. As
a result, all information about what had fallen in -
whether it be elephants or donkeys - would be erased. In a
riposte to Einstein's famous remark that God does not play
dice, rejecting quantum uncertainty, Dr. Hawking said in
1976, "God not only plays dice with the universe, but
sometimes throws them where they can't be seen."
That was a violation of quantum theory, which says that
information is preserved, and quantum theory is a
foundation of all modern physics.
Dr. Susskind, who along with Dr. Gerard 't Hooft of the
University of Utrecht in the Netherlands was among those
who rose to the defense of quantum theory, said, "Stephen
correctly understood that if this was true it would lead to
the downfall of much of 20th-century physics."
The notion that information is always preserved has gained
credence from recent results in string theory, which hopes
to produce a Theory of Everything that would explain all
the forces of nature.
Work by several theorists, including Dr. Andrew Strominger
and Dr. Cumrun Vafa, both of Harvard, and Dr. Juan
Maldacena, now at the Institute for Advanced Study, has
contributed to a strange new view of the universe as a kind
of hologram, in which the information about what happens
inside some volume of space is somehow encoded on the
surface of its boundary.
In such a picture, "there is no room for information loss,"
Dr. Maldacena explained. But, he added, it does not explain
what Dr. Hawking did wrong in 1974 or how information does
get out of the black hole.
In his new calculation, Dr. Hawking said that because of
quantum uncertainty, one could never be sure from a
distance that a black hole had really formed. There is no
way to discriminate between a real black hole and an
apparent one.
In the latter case an event horizon, the putative point of
last return, could appear to form and then unravel; in that
case the so-called Hawking radiation that came back out
would not be completely random but would have subtle
correlations and thus could carry information about what
was inside.
According to quantum theory, both possibilities - a real
black hole and an apparent one - coexist and contribute to
the final answer. The contribution of the no-black-hole
possibilities is great enough to suffice to allow
information to escape, Dr. Hawking argued.
Another consequence of his new calculations, Dr. Hawking
said, is that there is no baby universe branching off from
our own inside the black hole, as some theorists, including
himself, have speculated.
"I'm sorry to disappoint science fiction fans, but if
information is preserved there is no possibility of using
black holes to travel to other universes,'' he said
yesterday. "If you jump into a black hole, your mass energy
will be returned to our universe, but in a mangled form,
which contains the information about what you were like,
but in an unrecognizable state."
The new results are hardly likely to be the last word,
either about the black hole information problem or about
black-hole travel. Few physicists agree with the approach
Dr. Hawking is using in his new calculation. Nobody knows
how to weigh the different possibilities in such a quantum
calculation, said Dr. Sean Carroll of the University of
Chicago.
In conceding the bet, Dr. Hawking offered Dr. Preskill a
cricket encyclopedia but said that Dr. Preskill, being "all
American,'' refused. So Dr. Hawking had a copy of "Total
Baseball: The Ultimate Baseball Encyclopedia" flown in.
Dr. Hawking's partner in the bet, Dr. Thorne, is sticking
to his guns for now. Dr. Hawking commented, "If Kip agrees
to concede the bet later, he can pay me back later."
http://www.nytimes.com/2004/07/22/science/22hawk.html
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