Are black holes surrounded by walls of fire? Does this imply that one (or more) of our most cherished physical principles—and here I’m talking about biggies like quantum theory, the conservation of information or Einstein’s equivalence principle—is wrong? Any may our savior come in the form of wormholes? These are the questions consuming some of the world’s foremost theoretical particle physicists as they argue about potential solutions to what has become known as the “black hole firewall” problem—perhaps the most important paradox in physics since Stephen Hawking proposed his first black hole information paradox nearly four decades ago.
Every black hole has an event horizon. Nothing that moves inside a black hole’s event horizon will ever escape, not even light. Yet we’ve always understood event horizons to be less than dramatic—if you were to cross one, you wouldn’t notice anything immediately amiss.
Event horizons are important, however, for a number of reasons. Consider that according to the laws of quantum mechanics, a pair of virtual particles can jump into existence. Ordinarily, they quickly come back together and annihilate one another, but if the process happens near an event horizon, one particle can get sucked into the hole, leaving the other to drift into space. This implies that black holes radiate particles, a curious fact that Stephen Hawking pointed out many years ago. Eventually black holes lose so many particles that they shrink and die, having spewed their mass out into the cosmos in a stream of Hawking radiation.
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