One of physicist Stephen Hawking's most famous paradoxes may finally be solved: Black holes may in fact hang onto information about the massive stars that created them, new research indicates.
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This information may lurk in the radiation around black holes colloquially known as "quantum hair" and could, in theory, be retrieved to retell the origins of those black holes, the research suggests.
"[This research] is the final nail in the coffin for the paradox because we now understand the exact physical phenomenon by which information escapes a decaying black hole," Xavier Calmet, a professor of physics at the University of Sussex and lead study author, toldLive Science via email.
He suggests a modification to Hawking radiation that makes it "non-thermal" and thus capable of carrying information with it away from the final fate of the black hole.
These findings may finally resolve a thorny problem that Hawking was working on in his last years.
According to Stephen Hawking's work, radiation slowly "leaks" out of black holes in the form of thermal energy, which has come to be known as "Hawking radiation."
But because of its thermal nature, this radiation can't carry information.
That means that as black holes evaporate, they methodically destroy all information about the stars that created them.
This is contrary to the laws of quantum mechanics, which say that information cannot be destroyed and that an object's final state can reveal clues about its initial state.
This problem has troubled cosmologists for decades and is known as the "Hawking information paradox."
While black holes carry no "memory" of the stars they once were, the rules of quantum physics say that information can't simply be erased from the universe. In 1976, Hawking introduced a fly to this cosmic ointment by showing this information couldn't dwell indefinitely within black holes sealed away from the outside universe either.
Applying the rules of quantum mechanics to black holes, Hawking suggested they emit a type of thermal radiation, later called Hawking radiation.
Over immense periods of time, the leaking of this radiation causes black holes to completely evaporate, leaving only a vacuum behind. In this way, information is irretrievably lost.
In their new research, the team reassessed Hawking's 1976 calculations, but this time accounted for the effects of "quantum gravity",  the description of gravity according to the principles of quantum mechanics,  something Hawking hadn't done.
"While these quantum gravitational corrections are minuscule, they are crucial for black hole evaporation," Calmet said.
“We were able to show that these effects modify Hawking radiation in such a way that this radiation becomes non-thermal. In other words, factoring in quantum gravity, the radiation can contain information." ■