Media absurdity has reached new levels of darkness with the announcement that Stephen Hawking has a new theory in which black holes do not exist after all.
No, he doesn’t.
[Note added: click here for my new introduction to the black hole information paradox.]
First, Hawking does not have a new theory… at least not one he’s presented. You can look at his paper here — two pages (pdf), a short commentary that he gave to experts in August 2013 and wrote up as a little document — and you can see it has no equations at all. That means it doesn’t qualify as a theory. “Theory”, in physics, means: a set of equations that can be used to make predictions for physical processes in a real or imaginary world. When we talk about Einstein’s theory of relativity, we’re talking about equations. Compare just the look and feel of Hawking’s recent note to Einstein’s 1905 paper on the theory of special relativity, or to Hawking’s most famous 1975 paper on black holes; you can easily see the difference without understanding the content of the papers.
The word “theory” does not mean “speculations” or “ideas”, which is all that is contained in this little article. Maybe that’s what theory means at a cocktail party, but it’s not what “theory” means in physics.
Second, what Hawking is addressing in this note is the precise level of blackness of a black hole… in short, whether the name “black hole” for the objects we call black holes is really appropriate. But simply the fact that black holes aren’t quite black isn’t new. In fact it was Hawking himself who became famous in 1974-1975 for pointing out that in a world with quantum physics, typical black holes cannot be precisely black — so it’s not true that nothing ever comes out of a black hole. Black holes must slowly radiate elementary particles, a process we call Hawking radiation.
From day 1, Hawking’s observation posed puzzles about how conflicting requirements of quantum theory and Einstein’s gravity would be resolved, with quantum theory demanding that all information that fell into the black hole be neither destroyed nor copied, and Einstein’s gravity insisting that there is no way that the information of what went into a black hole can ever come out again, even if the black hole evaporates and disappears. The assumption of the community has long been that the 1970s calculation that Hawking did, while largely correct, leaves out a small, subtle effect that resolves the puzzle. The question is: what is the nature of that subtle effect?
No one, including Hawking, has posed a satisfactory answer. And that is why we keep hearing about black holes again and again over the decades, most recently in the context of the “firewall paradox”. In his recent paper, Hawking, like many of his colleagues, is proposing another possible answer, though without demonstrating mathematically that his proposal is correct.
But did Hawking really say “There are no black holes”, or didn’t he??
Talk about taking things out of context!!! Here’s what Hawking actually said.
First he suggests that the edge of a black hole — called its “event horizon”, a very subtle concept when you get into the details — really isn’t so sharp once quantum effects are considered. Many people have suggested one version or another of this possibility, which would represent a small but critical correction to what Hawking said in the 1970s (and to what people understood about black holes even earlier).
And then Hawking writes…
“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 the final clause, which is omitted from the media reports, and is absolutely necessary to make sense of his remark. What he means is that black holes are very, very slightly (though importantly) less black than he said in his 1974 paper… because the things that fall into the black hole do in some sense eventually come back out as the black hole evaporates. I say “in some sense” because they come out thoroughly scrambled; you, for example, if you fell in, would not come back out, even though some of the elementary particles out of which you are made might eventually do so.
And then he says
“There are however apparent horizons which persist for a period of time.”
Translation: for an extremely long time, what we call a black hole will behave in just the way we have long thought it does. In particular, there is no change in any of the astrophysics of black holes that astronomers have been studying in recent decades. The only issue is what happens as a black hole begins to evaporate in a serious way, and when you look very, very carefully at the details of the Hawking radiation, which is very difficult to do.
“This suggests that black holes should be redefined as metastable bound states of the gravitational field.”
In short: In Hawking’s proposal, it’s not that the objects that you and I would call “black holes” don’t exist! They are still there, just with a new name, doing what we’ve been taught they do except in some fine-grained detail. Not that this fine-grained detail is unimportant — it’s essential to resolving the quantum vs. gravity puzzle. But an ordinary person watching or exploring near a black hole would notice no difference.
Notice also all of this is a proposal, made in words; he has not shown this with mathematics.
In short, although Hawking is, with many of his colleagues, working hard to resolve the puzzles that seem to make quantum theory conflict with Einstein’s theory of gravity in this context, he’s not questioning whether black holes exist in the sense that you and I would mean it. He’s addressing the technical issue of exactly how black they are, and how the information contained in the things that fall in comes back out again. And since he’s just got words, but not math, to back up his suggestions, he’s not convinced his colleagues.
Meanwhile, the media takes the five words “There Are No Black Holes” and creates almost pure fiction, fiction that has almost nothing to do with the reality of the science. Well done, media, well done. Sometimes you’re just like a black hole: information comes in, and after being completely scrambled beyond recognition, comes back out again through a mysterious process that makes no sense to anyone. Except that in your case, it’s very clear that information is lost, and misinformation is created.
Hey! That’s a new theory of black holes! (I’ll write a 2-page paper on that this afternoon…)