According to this New Scientist article, Stephen Hawking now thinks that information in black holes may not be lost forever. He will make his case at the 17th International Conference on General Relativity and Gravitation in Dublin on 21st July. His last-minute request was granted solely based on his reputation, as details of the new theory are sketchy at best. Hints from a recent Cambridge seminar indicate that Hawking’s ‘new’ black holes may have no well-defined event horizon. Also, the GR17 website gives the following snippet:

The Euclidean path integral over all topologically trivial metrics can be done by time slicing and so is unitary when analytically continued to the Lorentzian. On the other hand, the path integral over all topologically non-trivial metrics is asymptotically independent of the initial state. Thus the total path integral is unitary and information is not lost in the formation and evaporation of black holes. The way the information gets out seems to be that a true event horizon never forms, just an apparent horizon.

A bit above my head, I’m afraid, but hopefully other SciScoop readers can enlighten me as to its meaning. We’ll have to wait until next Wednesday for the full details, but it promises to be an interesting talk.

There’s a good article on this in Nature. Hawking’s original view followed Einstein’s general theory of relativity, which predicts that, at certain locations in space, matter collapses into an infinitely small and dense point, called a singularity. It is infinitely small, and thus cannot possibly have any structure, so there is no way that it can hold information–any data about particles entering the black hole must be lost forever. But quantum theory says that any process can be run in reverse, so starting conditions can theoretically be inferred from the end products alone. This implies that a black hole must somehow store information about the items that fell into it.

Hawking has been attempting to combine quantum theory with general relativity in a powerful new theory of quantum gravity. He has been using a mathematical technique called the “Euclidean path integral”, which lumps all the possible histories of a system into one equation. First used by Richard Feynman, it has generally been applied to subatomic particles. But Hawking has been working for several years to apply the idea to black holes.

John Preskill, the theoretical physicist at the California Institute of Technology, Pasadena with whom Hawking had the bet, says that Hawking’s new take on quantum gravity rests on shaky mathematical foundations, and is unlikely to be embraced by the physics community. “I am sceptical about whether he has found a fully satisfactory resolution to the problem,” he says.