Hawking is the Cambridge University physicist who wrote the best-selling "A Brief History of Time." He has become one of the world's leading cosmologists -- that is, scholars on the origin and structure of the universe -- despite being confined to a wheelchair with Lou Gehrig's disease. He speaks through a mechanical voice synthesizer and laboriously writes his books and scholarly papers one letter at a time, on a special computer.
Since the 1970s, Hawking has insisted that black holes -- super concentrations of gravity created by burned-out stars -- swallow up matter and energy that never reappear, except as an unrecognizable flash of heat.
Physicists have long accepted the principle that the amount of energy and matter in the universe remains constant. You can convert matter into energy and back again, but the sum total stays the same. Hawking's black hole theory seemed to quarrel with that principle, creating one of the great arguments of science.
On 22 July, Hawking stood before hundreds of colleagues at the 17th International Conference on General Relativity and Gravitation in Dublin and said he had been wrong.
"I want to report that I think I have solved a major problem in theoretical physics that has been around since I discovered black holes radiate thermally 30 years ago. The question is, is this information lost in black hole evaporation?" Hawking said.
In a telephone interview with RFE/RL, Gerry Gilmore, a professor of experimental philosophy at Cambridge University, translates. "Now about 30 years ago, Stephen showed that actually stuff didn't disappear. It merely disappeared for a while. And then reappears in a flash of heat. And so matter of all different sorts -- you know, it could be you and me and planets and apples and oranges and even completely different sorts of matter like 'dark matter' and stuff that's completely different from us -- all disappears into there. And then after some very long time, it just reappears as pure heat. And so what that means is the universe loses the memory of what matter was made of, what different sorts of matter there were," Gilmore said.
In Dublin, Hawking went on to say that he has now discovered that information about matter swallowed up in a black hole isn't really lost after all. The black hole eventually disintegrates and disgorges the matter and energy in a distorted form. "This loss of information wasn't a problem in the classical theory. A classical black hole would last forever, and the information could be thought of as being preserved inside it, but just not very accessible. However, the situation changed when I discovered that quantum effects would cause a black hole to radiate at a steady rate," Hawking said.
Gilmore explains the significance of Hawking's change of view. It may disclose for the first time, Gilmore says, a logical link between the laws of quantum physics -- the normal mechanical world -- and the heretofore inexplicable contrary behavior of concentrated gravity.
"The hypothesis, the theory, is what Stephen calls a 'theory of everything.' The idea is that there's some underlying, more sophisticated theory of physics we haven't found yet that explains everything that happens in the universe. And somehow or other, this must link together quantum mechanics, which describes normal matter, and gravity. And we've got absolutely no clue as to what this connection might be. Except perhaps this is it. It looks like if he's right here, then here is a situation where very, very strong gravity -- which is the most interesting form of gravity, i.e. a black hole -- somehow or other is talking to quantum mechanics," Gilmore said.
Hawking's change of scientific position closed the book on a long-standing bet. John Preskill, a theoretical physicist at the California Institute of Technology, had bet Hawking that he eventually would be proven wrong. Preskill argued that when a star burns out, creating a black hole, matter sucked into the hole eventually would re-emerge.
Conceding the point, Hawking has delivered to Preskill his winnings -- an encyclopedia of baseball.
Hawking's new point of view has not been automatically endorsed by everyone in the world of science, however. Most physicists say they are waiting to read a detailed paper that Hawking is preparing to publish before making any final judgments.
Even Preskill, with his new encyclopedia in hand, says he is dubious. As he put it in an interview with the Associated Press: "I'll be honest. I didn't understand [Hawking's] talk."