According to much of the media, Steven Hawking says there’s no such thing as a black hole. This sounds really rad but is the media reflecting celebrity and titillating terminology rather than substance and veracity? Of course, Hawking is a media magnet, as are (ahem) Black Holes. Besides, didn’t Hawking write the book on black holes? Yes he wrote an influential papers on the subject. However, if you look at what he was saying then and what he’s saying now…for one thing, he’s not saying there’s no such thing as a black hole.
The actual quote from his recent paper (taken from a talk he gave in 2013) is, “The absence of event horizons mean that there are no black holes – in the sense of regimes from which light can’t escape to infinity.”
Notice, there are two parts to the sentence. The media generally picked up the first and ignored the second. Here and elsewhere in the paper, Hawking is dealing with a long-held belief in cosmology – the definition of a black hole says it is a phenomenon of space-time with an event horizon, such that when the event horizon is crossed nothing (not even light) ever comes back out. In practice, we are (with current technology) limited to observing apparent horizons. The apparent horizon, according to Hawking’s current thinking, is a quantum phenomenon in which it is (theoretically) possible for energy and information to escape a black hole. So, not really a black hole in the classical sense, but still a kind of black hole – black holes do exist.
Actually, Hawking’s paper addresses a relatively new problem known as the black hole firewall paradox. This theory holds that because of quantum mechanics at the atomic level, an event horizon is transformed into a highly energetic region, a ‘firewall,’ that incinerates all matter passing through it (like a hapless astronaut, for example). This theory is close to an abomination for some astrophysicists mainly because it does violence to Einstein’s theory of general relativity (the theory doesn’t hold in the event horizon firewall).
Hawking proposes another possibility – given current knowledge of quantum mechanics and general relativity, black holes do not have an event horizon to act like a firewall. Instead, there is no sharp boundary, only an apparent boundary (apparent horizon). In theory, the apparent horizon can dissolve, which would mean eventually energy trapped in a black hole could escape – no more, “…light can’t escape to infinity.”
Behind these ideas are worlds of math, and very little of it is settled. Hawking himself realizes that, “The correct treatment remains a mystery.” This is to say most of these ideas are thought experiments, backed by skeins of incredibly difficult math and perhaps questionable assumptions. Mainly, Hawking wishes to add to the arguments against the event horizon firewall paradox; he is not arguing against the existence of black holes.
So yes, most of the media is guilty (again) of running with celebrity and titillation rather than checking their facts and getting the story right. Should we be surprised? (Rhetorical question, of course.)