What was the bet about black holes that Stephen Hawking conceded this Summer?

Stephen Hawking has spent most of his illustrious career at Cambridge University in England studying black holes. Black holes are thought to be regions of space where gravity is so strong that nothing can escape, not even light. What that would seem to imply is that anything can go into a black hole but nothing can come out. In particular, all the information about what had fallen into the black hole was irretrievably lost. In the 1970's, Hawking suggested that the idea that nothing can escape from a black hole was not quite right. A black hole has a temperature, and that means that some form of heat can escape from the black hole. In fact, eventually a black hole will just evaporate into nothing. The heat contains no information about the black hole, however, so Hawking argued that the information was still lost.

This loss of information was the subject of a bet between Hawking and Cal Tech scientist Kip Thorne on one side and John Preskill, also of Cal Tech, on the other. Hawking and Thorne argued that indeed information is lost forever, but Preskill claimed that somehow the information about the inside of a black hole would be preserved.

Hawking now asserts that he has solved the problem, and the answer is the opposite of what he originally thought. In a complicated process (whose details remain to be discussed), information leaks out of a black hole, although not in any way that is easy to recognize. On the basis of this new idea, Hawking conceded the bet and paid off Preskill. The bet involved an encyclopedia, "from which information can be recovered at will."

Hawking also now rejects one other early idea about black holes, that the lost information disappeared into another universe. He now says, "The information remains firmly in our universe. I am 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, but in an unrecognizable state."

Black holes remain one of Nature's most mysterious phenomena, and this Summer's concession by Stephen Hawking does not solve all their riddles.

The conference at which Hawking presented his result, 17th International Conference on General Relativity and Gravitation, is described at: http://math.ucr.edu/home/baez/week207.html It does contain a link to a more detailed discussion of this result.

This week's question comes from Dr. Dave Thompson. Dr. Thompson is an astrophysicist who studies gamma rays in the Laboratory for High Energy Astrophysics. He helped build, test, and analyze data from EGRET on the Compton Gamma Ray Observatory, and he is now helping build part of the Gamma Ray Large Area Space Telescope (GLAST), scheduled for launch in 2006. His particular scientific interest is gamma-ray pulsars.