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Black holes and firewalls

by CIFAR May 2 / 13

Physicists have debated for decades what might be the fate of information falling into a black hole. For much of the twentieth century, Einstein’s theory of general relativity prevailed and the accepted view was that if a person crossed the point of no return–or event horizon—not much would happen. In 2012, this view was challenged by a team of theoretical physicists who argued instead that the event horizon is where space and time end, so the end result would be far more catastrophic.

e6-physics-equation“Based on the 2012 theory, you’re annihilated. End of story,” says Senior Fellow Patrick Hayden, part of CIFAR’s Quantum Information Processing program. “Theoretical physicists are calling the event horizon a ‘firewall,’ a double entendre, because the wall would prevent you from seeing a ‘fire’ rather than protect you from one.” Scientists, including Hayden, have been trying to­ figure out if there is a way out of this catastrophic reasoning. In a recent paper published in the Journal of High Energy Physics Hayden and his colleague offer a different perspective that overcomes the paradox. “When you start to think about the quantum mechanical physics of black holes, what it is really about is the nature of space itself,” he explains. “At the core of this question is how black holes treat the movement of information. In these thought experiments, then, quantum information theory provides just the tool to probe the fundamental physics. In our paper, computer science comes to the rescue.”

Since the catastrophic firewall theory was first proposed one year ago, it generated great debate and confusion, but no clear refutation. In January 2013, however, Hayden and his colleague pointed out a flaw. In order to test the theory, an observer must perform a huge quantum computation on the radiation coming out of the black hole. “In order to be able to confirm that this firewall exists, you’d have to perform a large computation on the radiation, and then try to jump into the black hole. And if it takes you so long to do the computation that the black hole no longer exists by the time you are done, then there is no more paradox.” Physicists have not yet succeeded in developing a unified theory of the principles governing the nature of the Universe. This work continues to push scientists’ understandings of how quantum mechanics relates to the general theory of relativity. If scientists succeed in connecting the two theories, physics will take a major leap forward.

This work was funded by CIFAR, the Canada Research Chairs program, the Perimeter Institute, and the Natural Sciences and Engineering Council.