If there’s one thing in physics that captures peoples’ imagination (besides time travel), it’s black holes. The regions of space-time so dense that nothing — not even a beam of light — can escape their gravitational pull seem to tug similarly on the human mind. But now, black hole pioneer Stephen Hawking has come out with a paper saying not just that we might have black holes all wrong — they might not even exist at all.
Black Hole Bio
“There are no black holes,” Hawking writes in a recent paper. He quickly qualifies that dramatic statement, however, by saying it’s only true “in the sense of regimes from which light can’t escape to infinity.” The objects themselves, already confirmed by astrophysicists, still exist, but just not the way we thought they did — if Hawking’s paper (based on a talk he gave last August) is right.
What’s going on is this: Classically, black holes have an event horizon surrounding them, which serves as the effective boundary of the black hole. Once you’ve gone past the event horizon, you can never get out again, no matter what, even if you’re a beam of light or a neutrino or something.
The problems come up when quantum physics, the crazy science of the very very small, enters the mix. A recent astrophysical paper suggested that when quantum physics is taken into account, the event horizon would actually be, as Hawking puts it, “surrounded by firewalls, bolts of outgoing radiation that would destroy any infalling observer.” This is at odds with the prevailing Einsteinian theory, as Nature elaborates:
Someone in free fall should perceive the laws of physics as being identical everywhere in the Universe — whether they are falling into a black hole or floating in empty intergalactic space. As far as Einstein is concerned, the event horizon should be an unremarkable place.
To resolve the firewall issue, Hawking suggests that — surprise! — there is no event horizon. Instead there is an “apparent horizon,” which doesn’t hold stuff back to be trapped forever, so much as just delay and scramble it. That’s what he means by, “There are no black holes.” The classical idea of a black hole as an object that never lets things go might be flawed.
Hawking’s analysis was published on arXiv, a preprint server, and thus hasn’t been peer-reviewed. The Nature story quotes a bunch of other physicists saying the idea is plausible, but it’s still a good idea to be skeptical of all this. There might be another solution to the firewall paradox that leaves black holes intact — or, Hawking might be wrong, and the right solution is something even crazier.
It’s hard to say because Hawking left the actual nuts and bolts of the idea to other researchers. “The correct treatment remains a mystery,” as he told Nature. (His 3-page paper contains not a single equation — though, don’t worry, it’s still fairly incomprehensible if you’re not severely into this stuff.)
So once again, Hawking’s work could transform everything we know about black holes. Maybe the universe’s most greedy objects do eventually let go of their treasures, under certain conditions. Whatever the case, odds are they won’t loosen their grip on the public imagination.