What did Stephen Hawkings just say about black holes? Is it a big thing?

See subject. His submission: *Information Preservation and Weather Forecasting for Black Holes*. Good stuff?

(Less importance: he’s an, if not The, official Famous Physicist. Has he been publishing with normal regularity, or nowadays is any old paper by him is big news?)

I’ve seen this lay article, but I like to get laid here better. Any additional synopses, comments, and take-always for the informed public by the local physicists?

I haven’t studied his paper in detail, but maybe I can provide come context as to the ongoing debate it is part of.

The larger frame is that of the black hole information paradox—roughly, the fact that information is generally conserved in all quantum processes, due to the way quantum systems evolve (‘unitarily’, meaning roughly that all probabilities must sum to one, and implying reversibility, i.e. it can be run backwards, and thus, any information from earlier times can be recovered by just running the evolution backwards) in the absence of measurements, while it seems to be lost when it comes to black holes. Basically, black holes evaporate via Hawking radiation, and what they evaporate into can be viewed as a thermalized gas, i.e. a state that contains no information due to the fact that all the particles are distributed randomly. But this seems to imply that the information of anything thrown into it is lost. However, we also expect that this evaporation will ultimately have a description in terms of a quantum theory, where unitarity, and hence information, ought to be preserved.

Indeed, at least for certain black holes in a special context, such a description is known, thanks to something called the AdS/CFT-correspondence, where a gravitational theory in a higher dimensional space can be described in terms of a quantum theory on its boundary. Unitarity indeed holds in this context, so many people believe it should also hold in more realistic settings (Hawking himself famously retracted his earlier stance, that information is, in fact, lost, thus conceding a bet with John Preskill).

However, a recent argument due to Almheiri, Polchinski, Marolf and Sully (AMPS) poses some difficulties for that resolution. Basically, in order to transport information out of the black hole, after roughly half the evaporation time, the black hole must be maximally entangled with the Hawking radiation it has already emitted (entanglement being a type of quantum correlation that exceeds classically possible correlations). However, due to a generic feature of quantum field theory, the radiation modes just inside the black hole horizon and just outside of it must similarly be maximally entangled. But, entanglement is monogamous: if system A is maximally entangled with system B, it can’t be entangled at all with another system C.

This in itself isn’t necessarily a problem, due to something called ‘black hole complementarity’, a proposal by Leonard Susskind that, roughly, says that there are two different stories that one can tell about a black hole, that of an infalling observer, and that of one staying outside. The insider now can verify the entanglement between modes across the horizon, while the outsider can verify that of the early Hawking radiation with the black hole (by waiting for more radiation to leak out). But nobody, it was thought, can do both, and so, each tells a consistent story; this proposal entails that the interior of the black hole and the far-away Hawking radiation are, in a sense, two ‘complementary’ ways of looking at the same stuff.

But AMPS now showed that there actually is a way to measure both entanglements in this setting, and thus, that it apparently violates monogamy of entanglement. To resolve this, they proposed that in fact, there is no black hole interior, and that thus there is no entanglement across the horizon; but this means, again due to a generic feature of the vacuum in quantum field theory, that the state of the degrees of freedom at the horizon must be thermal—anybody falling into a black hole will be incinerated by a massive blast of radiation!

This, however, is in conflict with the principle of equivalence in general relativity, which entails that, for a sufficiently large black hole, there is ‘nothing special’ at the horizon, because locally, every spacetime can be made to look flat. This is basically the foundational principle of general relativity.

So no matter what we do, it seems that something’s gotta give—either black hole evaporation isn’t unitary after all, and information is lost, or the equivalence principle breaks down, or for some reason the local field theory description of the black hole horizon is wrong. (For a good summary of the argument, see this blog post by John Preskill; he also has a couple more discussing the issue in more detail.) None of these options are especially appealing to physicists, and so the broad feeling is that the AMPS argument is wrong; but nobody can, so far, put their finger on why. This has led to a great amount of debate, with entire workshops devoted entirely to the discussion of this issue (narrowly avoided the ‘hotly debated’-pun there).

Hawking now appears to propose that the problem is avoided, because no actual event horizon ever forms; as I’ve said, I haven’t read the details of his proposal, so I can’t really comment on it. It is, however, only one in a long line of proposals, and time will tell which one, if any, can be made to work in detail, and I personally don’t think Hawking’s has a priori a greater chance than any of the others.

Nitpick: There is no such scientist as “Stephen Hawkings”.

Stephen Hawking, however, is a noteworthy physicist.

Half Man Half Wit: Thank you. That was a very informative post and I appreciate your effort (and skill) in making it.

Thanks to both.

As usual, mind blowing stuff.

Ok, while I think about it, this is the Nature article about the OP paper, with the title “Stephen Hawking: There are no black holes.” I also backtracked to AMPS in the Nature article "Astrophysics: Fire in the hole! Will an astronaut who falls into a black hole be crushed or burned to a crisp?"

Which raises a question on journalism, one more important to the other, and both more serious because it applies to such a prestigious journal. I know lay articles have to be grabby, and they notoriously lose a lot in translation from the originating science, and Headlines are notoriously worse than that.

“Burnt to the crisp” misses the point, entirely, considering the big picture. And Hawking was directly quoted in the OP hed. That’s some hell of a statement to make. Isn’t this Nature hed even more egregious? Hell, it made it to a political blog I read (where I found out about it), meaning, roughly, that there is a good chance somebody will say “There are no…” because The Famous Physicist said it. (Perhaps contemporary heds about Einstein on “reality”* were equally perverted–“alarmist,” in other contexts–and the societal harm is minor. But Nature is important.

I’m also interested as to clearing up/highlighting this because that I was a science and technology writer doing similar work, for a similarly (then) important archival magazine, and busted my ass, and had my ass busted, trying to get the job done right.
*Here I follow an observation of Nabokov which has stuck in my mind, and comes up particularly wity modern physics. In his own voice in the Afterword to Lolita: “…‘reality’ [is] one of the few words which mean nothing without quotes…”

In fact, the complete sentence may have even more resonance with physicists:
"The obtaining of such local ingredients as would allow me to inject a modicum of average “reality” (one of the few words which mean nothing without quotes) into the brew of individual fancy…

Sounds to me as though he should make up his mind.

Last year I spent four classes in school expalining event horizons, the loss of information, and spaghetti man (which I read in goddamn SH’s Brief History of Time) and now he pulls the rug from under me?

Wasn’t it hard enough for us high-school science teachers to teach it and now he changes the rules?
I’m gonna kick his wheelchair.

Interesting stuff. Now, I have to read a lot so that when some kid says in class “sir, is it true that black holes don’t exist?” I have the right answer for a 12-year-old.

First of all I join the others in commending Half Man Half Wit for his informative post. I myself have nowhere near this level of understanding of the subject. However, just want to make a comment regarding the above, which I wholeheartedly agree with. Nature is indeed a prestigious journal, but I’m not sure the same can be said for Zeeya Merali, who, although well credentialed on paper, is really just a freelance science journalist who writes popular articles and TV scripts for anyone with a few bucks. Some of his commentary doesn’t seem to make sense, at least to me, like this stuff:

Seems to me that what Hawking is saying is that the event horizon is more chaotic and less well-defined than previously thought. Whether he’s right or not, the event horizon will of course expand when the black hole gains mass, and I don’t see any dichotomy between that and some entirely different “apparent horizon”.

And this whole business of things happily escaping from black holes seems to be a complete misunderstanding of Hawking radiation. Hawking radiation has nothing to do with anything escaping from a black hole, but with interactions between the black hole and quantum fluctuations in empty space, and the black hole evaporates because it gains negative energy, not because anything escapes from it. The crux of the information paradox as I understand it, in the simplest terms, is that if information is completely destroyed, either by being removed from the universe behind an event horizon or by the black hole eventually disappearing entirely, then it destroys the principle of determinism because the consequences of everything that went into it are nullified. But I think Hawking might be suggesting that the paradox can be resolved if Hawking radiation is somehow influenced by the matter and energy entering the black hole.

Just to dwell another moment on this topic of escaping from black holes, the most convincing hypothesis I’ve seen to demonstrate why this is impossible comes from the Schwarzchild equations that describe the relativistic curvature of spacetime caused by a [non-rotating, to take the simplest case] black hole. It leads to some mindboggling conclusions, in particular the fact that beyond the event horizon, the time coordinate t and the radial coordinate *r *change places, and it’s the radial coordinate pointing toward the singularity that becomes timelike. Or in other words, the singularity at the center of the black hole is your future, and you can’t escape from it for the same reason that you can’t escape from next Thursday.

This reminds me of a previous discussion on black holes (http://boards.straightdope.com/sdmb/showthread.php?t=105536) where **The Bad Astronomer **said:

Which was based on a different speculation, but it does sound reminiscent of someone encountering a firewall at the event horizon! :stuck_out_tongue:

What he is saying is that there is no event horizon, but there is an apparent horizon which is where the outgoing light appears to be frozen to an observer. For black holes which stationery (time independent), the apparent horizon and event horizon coincide, but they only coincide asymptotically for non-stationary black holes as they settle down.

Another thing to note about the apparent horizon is that it’s the existence of an apparent horizon which is sufficient for Hawking (or Hawking-like) radiation.

Yes that is true, but he is saying that Hawking radiation is influenced by what is going on in the BH region because there is not a true event horizon.

That’s true, but the problem is the Schwarzschild solution is very symmetric (in both time and space), so it’s fair to ask what properties are actually due to its very symmetric properties and which are due to generic properties of realistic black holes and what happens when quantum effects are brought into play?

For the small fry like me, a decent looking Discovery piece on BH complementarity from 2012.

If it’s profoundly wrong also, please reply post to the author…

So (with reading the details … Or not):

Does “No event horizon” in any way shape or form mean “no black holes?,” at least according to Hawking? Can’t be, right?

Ie, is an event horizon necessary and sufficient for the definition?

Whatever the case, the Famed Explainer to the Masses (Brief… and Briefer…) has a lot of splainin to do.

Under the strict definition of a black hole, no event horizon = no black hole, but the problem with that definition is that it’s a little too restrictive and it can exclude objects which behave for most purposes just like black holes due to the global properties of spacetime they inhabit. A better definition would be in terms of a suitably well-behave apparent horizon.

Can these problems be resolved using a quantum theory of gravity? That is, do these problems only come about when using the description of gravity in terms of curved space?

Ah, the joy of Science, where absolutes only exist for about six months.

I refuse to listen to anything he says since he stopped posting here the moment he became slightly famous and I couldn’t point at his books and stuff and coolly say, “Yeah, I know him.” I’m petty like that.

An alternative idea is that quantum entanglement is not so strong as to work to change to the model of a black hole at all, you can go back to the pre-Hawking model.

These Hawking and followers seem to be working Very far from evidence.
Perhaps quantum entanglement is really a nonsense.
Perhaps it only applies to photons.

I worry that a detector to property X, is a detector that only detects particles of property X.

Besides, all the property detectors, all the experiments are trying to detect the properties that they are based on ,but not well understood…
A detector that that detects photon interactions must be based on photon interactions. Photon interactions are not well understood. The property may be arising due to the detector not the thing being detected ! … Or the combination…
Teleporting photons ? but that found photon 2 to be opposite photon 1, and since 2 is locked with 3, 3 is therefore the same as 1. Photon 3 is not photon 1, its just a match of it. it was not possible to measure photon 3 twice. They measured it only once. The interaction may be that if photon 2 CAN interact with photon 1, photon 3 must be its opposite. There must be other photon pairs that were not detected because the photon 2 did not interact… its selection of matching (interactable? ) photons.

Was it …

Help! I’m falling and I can’t get up!

Just kidding … :slight_smile:

Now isn’t this interesting…what has happened to the credulity of your most famous Independent Scientist, hmmmmmmmm? :rolleyes:

And what if it’s actually hollow. . . and full of stars!

If I understand it correctly, Hawking is saying that information falling into a black hole isn’t swallowed up forever- it just gets stuck for a really, really long time and is totally scrambled when it finally does come out. Like a British roundabout.