The black hole riddle -- solved!

Stephen Hawking does a U-turn on his theory of the parallel universe - and loses his bet in the process.

David Adam
July 22, 2004 5:37PM (UTC)

"I want to report that I think I have solved a major problem in theoretical physics." With those words the eminent physicist Stephen Hawking opened a lecture at a scientific conference in Dublin yesterday which, in true Hawking style, overturned decades of scientific thinking, surprised and thrilled many of his academic peers and left everyone else scratching their heads.

Speaking to an audience of more than 600 physicists and dozens of the world's media, Prof Hawking said he now believed that black holes, the mysterious massive vortexes formed from collapsed stars, do not destroy everything that is sucked into them. Instead, an abstract quantity called "information", which describes the core characteristics of every type of particle in the universe, leaks from the black hole over time.


The announcement marks a U-turn from Prof Hawking, who had argued that anything swallowed by a black hole was forever hidden from the outside universe. It has also lost him one of the most famous bets in science: in 1997 Hawking and fellow theoretical physicist Kip Thorne made a wager with John Preskill at the California Institute of Technology, who insisted that information carried by an object entering a black hole was not destroyed, and so could be recovered.

"I'm now ready to concede the bet," Prof Hawking said yesterday. At stake was an encyclopedia -- "from which information can be recovered at ease" -- of the winner's choice. "John is all American so naturally he wants an encyclopedia of baseball. I had great difficulty finding one over here, so I offered him an encyclopedia of cricket as an alternative," Prof Hawking said. "But John wouldn't be persuaded of the superiority of cricket."

The about-turn ends a 30-year personal struggle for Prof Hawking. In 1974, while formulating new equations in an attempt to unite the heavyweight ideas of quantum mechanics and general relativity, he realised that black holes must emit heat, now known as Hawking radiation. The problem was that this radiation would carry energy away, meaning the black hole would gradually evaporate and then disappear in a final explosive outburst -- taking the crucial information with it.

This contradicts the fundamental laws of quantum physics, which insist the information can never be totally wiped out.

While several physicists over the years offered solutions to this paradox, Prof Hawking preferred to believe that the intense gravity inside a black hole somehow unravelled the quantum laws. More intriguingly, he suggested that the vanishing information might travel through the black hole to a parallel universe -- planting the seeds for a staple of science fiction.

"There is no baby universe branching off as I once thought," Prof Hawking admitted yesterday. "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. 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."


His new calculations suggest the surface of the black hole, the event horizon, has fluctuations that allow the information to escape. "It is great to solve a problem that has been troubling me for nearly 30 years, even though the answer is less exciting than the alternative I suggested."

He presented his new work at a hastily scheduled session at the 17th international conference on general relativity and gravitation at the Royal Dublin Society. Such is his reputation, conference organisers allowed him to speak without previously seeing the work. Prof Hawking's talk has been eagerly awaited for weeks after news of his change of thinking emerged when he spoke at a department seminar in Cambridge.

Gerry Gilmore, an astrophysicist at Cambridge University and a colleague of Prof Hawking, said: "At the moment everyone is reserving judgment, but Steve doesn't say things like this very often and so it's highly likely he's on to something interesting. What it is may well be so esoteric that it's not obvious to a non-expert, but then he's not talking to non-experts."

He said the findings could shed more light on quantum gravity -- a puzzling concept that emerges when physicists try to resolve the forces of gravity, which describes how the universe works on its biggest scale, and quantum mechanics, which only works on the smallest.


Prof Hawking shot to fame with his best-selling book "A Brief History of Time," which tried to explain how the universe works to a general audience. Despite being virtually paralysed with amyotrophic lateral sclerosis since his mid 20s, he travels the world on speaking engagements, communicating with a speech synthesiser and a hand-held device to select words. His speech comes five months after he survived a near-fatal bout of pneumonia, and follows a police inquiry into allegations of domestic violence against his wife, who was cleared of any wrongdoing.

After being given the baseball encyclopedia, which was flown to Dublin for the occasion, Prof Preskill said he was very pleased to have won the bet but added: "I'll be honest, I didn't understand the talk." He said he was looking forward to reading the detailed paper Prof Hawking is expected to publish next month.

David Adam

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