Dear Friend of CIFAR,

Black holes are seemingly the most violent places in the Universe. They are so dense and their gravitational pull is so strong that nothing can escape from them, not even light.

But what about information? If you dropped your iPhone into a black hole, would it permanently erase and destroy the device’s memory? Would the information on that memory disappear forever? Strangely enough, there’s a good chance that not only does the information come back, it comes back fast – like a reflection in a Black Hole Mirror.

The Black Hole Mirror concept is based on the same principles that might someday make quantum computing a reality. In fact, engineers are already applying these principles to distribute software and stream video over the internet.

Black holes form when massive stars run out of nuclear fuel, collapse and become so compressed that nothing seems to be able to escape their gravitational pull. They may sound like the stuff of science fiction, and astronomers can’t see them directly, but there is strong evidence that millions of black holes exist in our galaxy alone.

Black holes have become metaphors for the great unknown. Decades after being predicted, they remain a puzzle that threatens long-established and cherished physical laws.

Leonard Susskind, a theoretical physicist and associate member of CIFAR’s Cosmology and Gravity program, has had a long-standing debate with Stephen Hawking, the world-renowned astrophysicist, about whether or not information is lost forever once it enters a black hole. Dr. Hawking theorizes that a black hole swallows and permanently obliterates physical information. But this assertion goes against one of the principles of quantum mechanics that Dr. Susskind supports strongly: that information is never created or destroyed in a quantum process.

My colleague John Preskill and I approached this problem by imagining two citizens of an advanced civilization, Alice and Bob. Alice wants to destroy some information (in the form of quantum bits that are 0 and 1 simultaneously) by launching it into a black hole. Bob tries to recover this information by collecting radiation from the black hole.

Previous work showed that if Alice dropped her bits into a relatively young black hole, Bob would have to collect the radiation for half the life of the black hole before being able to decode a fraction of Alice’s information. In our new study, Alice waits until after the black hole has reached the halfway mark to drop her information. In the meantime, Bob prepares some information of his own – quantum bits that he entangles with Alice’s bits. Because this information is entangled, it is immediately linked to Alice’s information across any distance. So Bob’s task of recovering the information, by collecting the radiation from the black hole, speeds up significantly. The black hole becomes a mirror of information.

This work shows that when it comes to information, black holes aren’t as perfectly black as they seem – they are actually helping to illuminate the path to quantum computing.

Best wishes from the frontiers of human knowledge.

Patrick Hayden

Scholar, Quantum Information Processing program

Canadian Institute for Advanced Research
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