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Hawking Cracks Black Hole Paradox


By Jenny Hogan

New Scientist


After nearly 30 years of arguing that a black hole destroys everything that falls into it, Stephen Hawking is saying he was wrong. It seems that black holes may after all allow information within them to escape. Hawking will present his latest finding at a conference in Ireland next week.


The about-turn might cost Hawking, a physicist at the University of Cambridge, an encyclopedia because of a bet he made in 1997. More importantly, it might solve one of the long-standing puzzles in modern physics, known as the black hole information paradox.


It was Hawking's own work that created the paradox. In 1976, he calculated that once a black hole forms, it starts losing mass by radiating energy. This "Hawking radiation" contains no information about the matter inside the black hole and once the black hole evaporates, all information is lost.


But this conflicts with the laws of quantum physics, which say that such information can never be completely wiped out. Hawking's argument was that the intense gravitational fields of black holes somehow unravel the laws of quantum physics.


Other physicists have tried to chip away at this paradox. Earlier in 2004, Samir Mathur of Ohio State University in Columbus and his colleagues showed that if a black hole is modeled according to string theory - in which the universe is made of tiny, vibrating strings rather than point-like particles - then the black hole becomes a giant tangle of strings. And the Hawking radiation emitted by this "fuzzball" does contain information about the insides of a black hole (New Scientist print edition, 13 March).


Big Reputation


Now, it seems that Hawking too has an answer to the conundrum and the physics community is abuzz with the news. Hawking requested at the last minute that he be allowed to present his findings at the Seventeenth International Conference on General Relativity and Gravitation in Dublin, Ireland.


"He sent a note saying 'I have solved the black hole information paradox and I want to talk about it'," says Curt Cutler, a physicist at the Albert Einstein Institute in Golm, Germany, who is chairing the conference's scientific committee. "I haven't seen a preprint [of the paper]. To be quite honest, I went on Hawking's reputation."


Though Hawking has not yet revealed the detailed maths behind his finding, sketchy details have emerged from a seminar Hawking gave at Cambridge. According to Cambridge colleague Gary Gibbons, an expert on the physics of black holes who was at the seminar, Hawking's black holes, unlike classic black holes, do not have a well-defined event horizon that hides everything within them from the outside world.


In essence, his new black holes now never quite become the kind that gobble up everything. Instead, they keep emitting radiation for a long time, and eventually open up to reveal the information within. "It's possible that what he presented in the seminar is a solution," says Gibbons. "But I think you have to say the jury is still out."


Forever Hidden


At the conference, Hawking will have an hour on 21 July to make his case. If he succeeds, then, ironically, he will lose a bet that he and theoretical physicist Kip Thorne of the California Institute of Technology (Caltech) in Pasadena made with John Preskill, also of Caltech.


They argued that "information swallowed by a black hole is forever hidden, and can never be revealed."


"Since Stephen has changed his view and now believes that black holes do not destroy information, I expect him [and Kip] to concede the bet," Preskill told New Scientist. The duo are expected to present Preskill with an encyclopedia of his choice "from which information can be recovered at will".



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