Hawking: Black holes store information

Black holes preserve information about the stuff that falls into them, according to Prof Stephen Hawking, the BBC reports.

Physicists have long argued about what happens to information about the physical state of things that are swallowed up by black holes.

It was thought that this information was destroyed, but it turned out that this violated laws of quantum physics.

Prof Hawking now says the information may not make it into the black hole at all, but is held on its boundary.

"The information is not stored in the interior of the black hole as one might expect, but in its boundary - the event horizon," he told a conference at the KTH Royal Institute of Technology in Stockholm, Sweden.

In basic terms, black holes are a region in space where the gravity is so strong that nothing that gets pulled in - even light - can escape.

At the same time, the laws of quantum mechanics dictate that everything in our world can be broken down into information, for example, a string of 1s and 0s. And according to those laws, this information should never disappear, not even if it gets sucked into a black hole.

But Prof Hawking believes the information doesn't make it inside the black hole at all. Instead, it is transformed into a 2D hologram at the surface of the black hole's event horizon - the black hole boundary, or point of no return, where escape from the gravitational pull becomes impossible.

Working with Cambridge colleague Prof Malcolm Perry (who spoke afterward) and Harvard professor Andrew Strominger, Hawking has formulated the idea that information is stored in the form of what are known as super translations.

"The idea is the super translations are a hologram of the ingoing particles," Hawking explained.

"Thus, they contain all the information that would otherwise be lost."

Light particles - or photons - can be emitted from black holes due to quantum fluctuations, a concept known as Hawking radiation. Information from the black hole might be able to escape via this route.

But, Prof Hawking says it would be in "chaotic, useless form," adding: "For all practical purposes the information is lost."

If the information was not in this chaotic form, an observer might be able to reconstruct everything that had fallen into the black hole over a vast amount of time.