Stephen W. Hawking threw in the towel, or at least an encyclopedia, yesterday.
Hawking, the celebrated Cambridge University cosmologist and best-selling author, declared at a scientific conference in Dublin, Ireland, 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 John Preskill, a physicist from the California Institute of Technology, with a baseball encyclopedia.
The encyclopedia was the stake in a famous bet that Hawking and another Caltech physicist, Kip Thorne, made with Preskill in 1997. Hawking and Thorne said that information about what had been swallowed by a black hole could never be retrieved from it; Preskill and many other physicists said it could.
This esoteric-sounding debate is of great consequence to science because if 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, Hawking has concluded that physics is safe and that 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.
"Until Stephen's recent reversal, he was about the only person still getting it wrong," said Leonard Susskind, a theorist at Stanford University
Hawking spoke yesterday at the 17th International Conference of General Relativity and Gravitation. He was added to the program 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. Hawking, 62, who has amyotrophic lateral sclerosis, or Lou Gehrig's disease, 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 globe constantly, training generations of graduate students at Cambridge and writing books, including the popular A Brief History of Time.
Theorists have worried about the fate of information in black holes since the 1960s. In 1974, 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 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 Albert Einstein's assertion that God does not play dice, rejecting quantum uncertainty, Hawking said in 1976 that "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.
The notion that information is always preserved has gained credence from recent results in string theory, the hot area of research that hopes to produce a Theory of Everything that would explain all the forces of nature. This strange new view of the universe depicts it 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, no information is lost.
In his new calculation, 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, Hawking argued.
Another consequence of his new calculations, 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."