Stephen Hawking: 'Black Holes Ain't as Black as They Were Painted'

Professor Stephen Hawking speaks at a media event to launch a global science initiative at The Royal Society in London, July 20. Neil Hall/Reuters

Black holes "ain't as black as they were painted," Stephen Hawking told his audience Monday evening at a public lecture in Stockholm. The renowned physicist was in town for a conference at the KTH Royal Institute of Technology. Black holes "are not the eternal prisons they were once thought," Hawking said, according to The Washington Post. "Things can get out of a black hole. So if you feel you are in a black hole, don't give up. There's a way out!"

On Tuesday, he delved into a technical presentation about his new thoughts on black holes—namely how information might escape one. The idea could finally resolve the black hole information paradox physicists have been grappling with for years, without upending our understanding of how the universe works.

"This has been an outstanding problem in theoretical physics for the last 40 years," Hawking told a much smaller audience of top physicists at the conference, organized by University of North Carolina physicist Laura Mersini-Houghton and dedicated to tackling this paradox. As of yet, Hawking said, "no satisfactory resolution has been advanced."

At the core of the information paradox is the tension between two theories of nature, which are "perhaps the two most successful theories in the history of science," says Dan Hooper, a theoretical astrophysicist at Fermilab.

On one hand is general relativity, which says that anything that enters a black hole is lost in the immense power of its gravity and that a black hole eventually destroys any information—location, velocity and orientation, for example—about what it has swallowed up, including the star that birthed the black hole. On the other hand stands the theory of quantum mechanics, which says that information can never be lost.

Four decades ago, Hawking said that when something fell into a black hole, the information contained in it was erased, permanently irretrievable. He also posited that black holes have a sort of surface called the event horizon, the boundary where things can and cannot escape from its gravity. Black holes, he posited, give off radiation from their surface. But that radiation—which came to be known as Hawking radiation—would just contain random noise rather than information.

While Hawking insisted for a long time that information was irretrievable, other theoretical physicists like Leonard Susskind and Gerard 't Hooft opposed his view. The debate over whether information is lost in a black hole has been going on for years. Now Hawking has reversed course, announcing that he and colleagues Malcolm Perry at Cambridge and Andrew Strominger at Harvard have developed an explanation about where the information goes.

"The information is not stored in the interior of the black hole as one might expect, but on its boundary—the event horizon" in the form of super translations, or a two-dimensional hologram, Hawking said Tuesday. As a black hole steadily emits Hawking radiation, that information gradually passes back into the universe "in a chaotic and useless form. For all practical purposes, the info is lost."

In other words, it would be possible in principle to learn about the star that formed a black hole and other ingoing objects from the information returned in the Hawking radiation, but in practice it would be nearly impossible. At his public lecture, Hawking compared the phenomenon to burning an encyclopedia. As The Washington Post reporter Rachel Feltman puts it, "You wouldn't technically lose any information if you kept all of the ashes in one place, but you'd have a hard time looking up the capital of Minnesota."

Hawking and his colleagues plan to publish a scientific paper in the near future, BBC News reports, which will go into more mathematical detail and help parse out if and how the idea presented Tuesday differs from previous theories. But if in fact the idea is sound, it could be a major milestone for theoretical physics.

"Of all the open questions in physics none is more ambitious and important than trying to figure out how general relativity and quantum mechanics somehow manage to work together so consistently," says Hooper, who explains that addressing questions about black holes is "perhaps the most fruitful approach that we've had in recent years to solve this question."

"Black holes are a special circumstance where both gravity and quantum mechanics are important," he says. "If we can understand how they work, this bigger question of how general relativity and quantum mechanics work together or unify might become more clear."

If you'd like to take a crack at deciphering Hawking's technical explanation, KTH has uploaded a roughly nine-minute video to YouTube: