Whether or not information can truly be lost is a major issue in the study of black holes. Stephen Hawking’s work in the 1970s offered a mechanism for black hole evaporation. Vacuum fluctuations would cause a particle and its antiparticle to appear just beyond the black hole’s event horizon, with one of the two falling into the black hole while the other escaped. A ‘virtual’ particle, in other words, would become a real particle. Black holes, in this view, would be able to lose mass through quantum effects, a theory that the soon to be launched GLAST satellite will try to confirm.

Black hole and accretion disk

But ingenious as Hawking’s theory was, it produced a conundrum. Black holes that fail to gain more matter will eventually vanish, with information, such as the identity of matter drawn into the black hole, becoming permanently lost. It being a linchpin of quantum mechanics that information cannot be lost, this presents a problem. Enough of one that physicist John Preskill (Caltech) bet Hawking and Kip Thorne (also at Caltech) that information could not be lost in black holes. Hawking conceded in 2005, and now a team of physicists has suggested a new way of seeing black holes that would indeed allow information to escape.

Image: An artist’s depiction of the accretion of a thick ring of dust into a supermassive black hole. The accretion produces jets of gamma rays and X-rays. Credit: ESA / V. Beckmann (NASA-GSFC).

The idea behind this work, led by Abhay Ashtekar (Penn State), is that the disappearance of information is only an illusion. Think of spacetime as a series of individual building blocks. Ashtekar’s team believes that the idea of a continuum is but an approximation of a larger reality, one in which singularities, as Ashtekar himself says, “…are merely artifacts of our insistence that space-time should be described as a continuum.” Thus:

“Information only appears to be lost because we have been looking at a restricted part of the true quantum-mechanical space-time. Once you consider quantum gravity, then space-time becomes much larger and there is room for information to reappear in the distant future on the other side of what was first thought to be the end of space-time.”

The work, to be published in the Physical Review Letters, draws on mathematical studies of black holes in two dimensions, an approach the team believes accurately applies to real black holes in four-dimensions, although directly studying the latter is what Ashtekar and company are now proceeding to do. If confirmed, their work would validate Hawking’s decision to pay off the bet with Preskill, which he did by giving the physicist what he had asked for, a baseball encyclopedia. Thorne has yet to concede the bet, for Hawking’s own take on how black holes might leak information is as controversial as Ashtekar’s is likely to be.