## Sunday, January 26, 2014

### Bizarre Hawking: black hole work was my biggest blunder

By rejecting event horizons, Hawking has morphed into a hardy defensible maverick

A few days ago, Stephen Hawking wrote a paper arguing that firewalls are pure crap (so far so good) because they violate CPT, much like black hole remnants (it's no good anymore: these objects are wrong but not because of CPT violation).

The world's most famous theoretical physicist along with his high-tech friend

But he also says that event horizons violate CPT as well, they can't exist (see the media echo chamber that puts Hawking into the black holes don't exist category), and the right resolution is that the surfaces of black holes are chaotic like turbulence and predictions are as impossible in practice but possible in principle as (long-term) predictions in meteorology. Well, I would say that "surfaces this chaotic" would act as firewalls. Moreover, event horizons that are as perfect as in classical theory violate CPT but event horizons which allow the Hawking radiation (unlikely but in principle allowed violation of the causality) are compatible with CPT!

So I don't really believe that Hawking's criticism of event horizons is kosher.

Hours ago, Fox News and Nude Socialist have upgraded this Hawking story to a higher level:
Black hole theory my 'biggest blunder,' Stephen Hawking says (Fox)

Stephen Hawking's new theory offers black hole escape (NS)
Wow.

While I have sympathized with Hawking's unambiguous indication that the firewall theory is wrong, his claims that the black holes don't exist at all – and he is saying that because a black hole is defined by its having an event horizon, so if no objects possess event horizons, it means that there are no black holes – is a little bit too much of a good thing.

As you know, Albert Einstein has used the term "my biggest blunder" for the concept of the cosmological constant, an additional term (they would translate the term as the "cosmological member") that he inserted into his pristine Einstein's equations of general relativity in order to supplement the Universe with a repulsive force that protects the Universe from collapsing (the collapse is what the attractive forces between galaxies in the Universe want to achieve). In reality, the cosmological constant is indeed positive and of the same order that Einstein was imagining. However, it's actually slightly larger (by a factor of order 2) so it's enough not only for stabilizing the Universe but it makes the expansion of the Cosmos accelerate.

(The stabilization of the attractive and repulsive forces that was envisioned by Einstein wouldn't work anyway because the balance would be unstable: a tiny deviation from the "perfect balance" in either direction would be exponentially growing in time.)

The great physicists' criticism of their famous theories as the "biggest blunder" may look analogous – they have the right to criticize their ideas, it's sort of "cool", and both of their criticisms end up being wrong – but there's still a difference. The cosmological constant was something like Einstein's tenth most important contribution to physics, maybe the twentieth. However, the insights on black hole thermodynamics are (by far) Stephen Hawking's #1 contribution to science so Hawking's present criticism is "bolder".

I like his focus on symmetries, in this case CPT. He says that remnants, firewalls, and even event horizons violate CPT because they introduce "new arrows of time". But the event horizons actually don't – and ironically enough, the reason why they don't introduce any time-reversal asymmetry or CPT violation is nothing else than the Hawking radiation. To be candid, I must say that the remnants and firewalls don't violate the CPT, either – although they're wrong for other reasons.

The black holes may swallow matter and their event horizons look like a one-way membrane. This would be a violation of CPT. But the claim that the event horizons are one-way membranes is just a statistical claim, like all the claims about the "mostly increasing entropy" according to statistical physics. It is not strictly impossible for matter to get out of the black hole through the event horizon, i.e. in the "opposite than normal" direction. It's just very unlikely!

In this sense, the black holes don't differ from the furnaces. Coal only seems to be moving in one direction – into the furnace – but in principle, things like coal may escape from the furnace, too. It's just very unlikely that the ashes and smoke that leave the furnace combine themselves into a large chunk of coal.

The black hole Penrose diagrams are CPT-violating – time-reversal asymmetric – but this asymmetry is not a fundamental microscopic law of Nature. Instead, the reason why we don't revert the picture above upside down is that it is simply extremely unlikely for a black hole, an object, to "emit" a Hawking radiation that looks like a star. Such a backward evolution would be reducing the entropy and this is very unlikely.

We are only discussing the diagram above – which only has the singularity in the future but the past looks like a topologically/causally empty Minkowski space (with a star) – because the time-reverted process is exponentially unlikely so it won't ever appear in practice (if the black hole is large enough). But it is not strictly prohibited. The previous sentence is the reason why Hawking's claims that event horizons inevitably violate CPT is just invalid.

The eternal black hole starts with an initial singularity ("white hole") and the configuration is CPT- or time-reversal-invariant. Large objects would be extremely unlikely to move through the "antihorizons" which is why the object above can't be combined with any other matter to yield a plausible process in the real world. The Penrose diagram must be modified by replacing the "white hole" (past portion of the spacetime) by the collapse of the star (or something else) – we get the previous realistic picture. Similarly, the previous realistic picture emits a near-thermal Hawking radiation into the future (while doing so, the total entropy of the hole plus radiation is going up, too). If time-reverted, we obtain a near-thermal incoming and convergent (high-entropy) Hawking quanta, an initial state that has no reasons to be discussed because it's hugely exponentially unlikely (the entropy would be decreasing when the quanta combine into a black hole, too).

Einstein said that the cosmological constant was his "biggest blunder" more than half a century before the experimental discovery of a nonzero cosmological constant (in the late 1990s). Most cosmologists and theoretical physicists tended to believe that the cosmological constant was exactly zero before it was experimentally found that it was strictly positive. The experimental case for the existence of black holes – with event horizons – is arguably equally strong as the case for the cosmological constant, if not stronger. So Hawking's repentance is arguably much more embarrassing than Einstein's. The Hawking radiation hasn't been experimentally found but it's extremely well theoretically understood and it's theoretically clear that black holes with event horizons and the Hawking radiation don't violate CPT and don't suffer from any other lethal problems suggested by Hawking.

For decades, I have been impressed by Hawking's being so right about so many cutting-edge questions (except for some important exceptions where he lost the bets, of course, like the information loss, the existence of the Higgs, and some others), despite all the hurdles he is overcoming while forming his own opinions. Unfortunately, his rejection of the black hole has changed this impression in a significantly negative direction. It's silly not to believe that black hole horizons exist.

1. Cut the old man some slack. Judge him by his younger days or else we all will hang.

2. Einstein's self admitted greatest blunder not only wasn't a blunder after all-well, not in quite the way he thought anyway-it was far from being the greatest, which is obviously the fact that he spent the last years of his life trying to do away with quantum mechanics, or at least the parts of it he didn't like.

In that sense, Einstein's real greatest blunder wasn't in the ranking of his contributions to science, it is what he *didn't* contribute to science.

3. If one just considers that a black hole is an approximation of one of those universa (corresponding to a particular 'M-theoretical vacuum-geometry') that collapses 'back to where it came from', then isn't it less of a lapse of logic to say that black holes don't exist?

I think it is less of a lapse if only since a universe did not exist before it was spawned similar to any of us not existing before we got biochemically conceived and apparently also born;

Except, of course, as a potential projection of a not in every respect infinite, but eternally platonic, timelessly energy producing, then typically in a timely fashion evolutionary process that patterns (and makes e.g. 3D space for) this energy patterning tendency/aspect of What Is (or the Multiverse).

So, I suggest that Hawking's mental and electronic talkings might not be figurings as farfetched as they seem at first.

:->

4. Is there still a singularity at the center that refuses to really form since time stops instead as far as external observers are concerned?

5. I really don't understand his comments about CPT. a CPT-violating field configuration and a CPT-violating theory are two entirely different beasts.

best
kristan

6. Quite right, and this correct comment of yours is the seed of the elementary mistake that Hawking is making.

Well, more precisely, Hawking doesn't assume that configurations have to be invariant under CPT separately. He's not that silly.

But he's probably noticing that the CPT-transformed "partners" of the well-known configurations (like a star collapsing to a BH that evaporates later) are not being discussed, so he assumes that they don't exist at all and they're not allowed by the laws of physics. That would mean that the *theory* violates CPT.

But it doesn't violate CPT because the configurations are allowed, they're just exponentially unlikely for completely analogous reasons to any other process with a decreasing entropy, like "antidiffusion".

Cheers
LM

7. Nice defense, Luke, but I haven't really considered Hawking to be old in the sense of senile. Even very recently, he would be very sane and fast-thinking. That's what decides about my being surprised.

8. Darn, that will feed the anti theoretical/fundamental physics trolls of all kind ... :-(

And the most embarassing thing is that popular media as always blindly magnify such things by trompeting them as loud speakers into the whole world ...

So I guess today Sheldon would no longer look so happy sitting beside Hawking either as on the picture above ... ;-)

9. In any case It takes exceptional amount of human greatness and scientific integrity to raise doubts to someone's own #1 work. much the same scientific integrity that climate alarmists fail practicing.

aside from that, Lubos, what do you mean by the "experimental case for the existence of black holes with event horizons"?

10. Hm, but I suspect that fournasses can easily produces trolling books which contain more entropy and less valuable information than ashes, smoke, etc ... ;-P

11. Stephen Hawking’s credibility as an interlocutor for and within the scientific community was greatly diminished by his recent decision to boycott Israel and thus demonstrate his open willingness to violate the principles of academic freedom. His thoughts no longer deserve the reverence with which others treat them.

12. I agree that in general (that is not counting special cases of illness senility) or older scientists (and even mathematicians) are not less smart than the young ones. However, there is little doubt that as you gets older you become less productive, not necessarily because you are less “smart” but because you have less energy, your start having health problems etc., the usual stuff. One result of this is that older scientists much less often come up with big new results, that put them “in the limelight”.

This is no problem for those scientists who shun publicity and find complete gratification in their work alone. I know know of a very famous mathematicians who when he got older continued producing very interesting work, but stopped going to conferences and even publishing so the only way to find out about his results was by talking to him. This man did not care at all about fame and publicity (he was famous enough) and continued to work essentially for his own pleasure. There are probably quite many cases like this. But there are also people who can’t live in “the shadow” and I think no one more so that Hawking (perhaps for the reasons that naturally come to mind).

Now that it is much harder for him to come up with exciting new discoveries the easiest way to attract attention is by announcing that he has changed his mind about something. He has been doing a lot of this in recent years and every time he does that, it is a world wide sensation. Indeed, he has succeeded in doing the kind of thing very few people can get away with: becoming famous for a discovery and even more for announcing that he has changed his mind about it.

13. Even the best make mistakes occasionally. Hawking made a rather big one in the late 80's with his idea that the arrow of time would reverse during the collapse of a closed universe.

14. Hey, wait a minute! I got an idea... about black holes and stuff :-D

15. Dear Bill,

I doubt that Einstein then or Hawking now face any "risk" when they denounce their important work, so in this sense, I don't think it's really courage. Instead, Hawking is effectively saying "look, I did it again" and "I could have made fun of you and mislead for 40 years because I am superior over you". Except that what he said then was right.

The experimental evidence for black holes has existed for decades. The evidence for horizons is really that there is a very dark object that swallows matter but radiates than any astrophysical object without an event horizon. See e.g. this paper about the hole in the Milky Way center

http://arxiv.org/abs/astro-ph/9706112

which has 380 citations now. I had a term paper and talk at Rutgers about it 16 years ago. At that time, I carefully studied the evidence for black holes and since that time, I have considered questioning black holes just plain silly.

Cheers
LM

16. kashyap vasavadaJan 27, 2014, 5:27:00 PM

Interesting comment Lucretius! Can you name the famous mathematician who did not want to publish in his old age?

17. kashyap vasavadaJan 27, 2014, 5:45:00 PM

Well! Unfortunately I do not know enough to have a definite view in this interesting debate. But my guess is that Hawking thinks that final theory of quantum gravity might modify concept of black hole drastically. So he wants to keep his options open!!

18. kashyap vasavadaJan 27, 2014, 5:50:00 PM

Let me add something; But unfortunately the news media have interpreted his paper as saying that black holes do not exist!! I do not know if he realized this danger. His paper does not have a single equation!

19. kashyap vasavadaJan 27, 2014, 6:11:00 PM

Hi Lubos: A question: My understanding is that in field theory at each instant CPT has to be conserved. If black hole preserves CPT over the whole life time there may be issues. I would like to be corrected if this is wrong.

20. Dear Kashyap, CPT isn't a linear operator on the Hilbert space, it is an antilinear operator, so it doesn't have eigenvalues like +1 or -1, something you seem to be imagining.

So CPT (and analogously T, if relevant) isn't behaving like CP or P or C. The symmetry under this transformation cannot be rephrased as a conservation law.

21. And he's damn right about it.

22. kashyap vasavadaJan 27, 2014, 6:48:00 PM

Thanks Lubos. I knew about antilinearity but I did not think
about it in this way. If I understand what you are saying is that because of
this it is ok for black holes to preserve CPT over the whole lifetime. On the
other hand particle physics reactions are isolated microscopic processes. So each event has to preserve CPT. Do you agree?

23. The breaking of time reversal symmetry results in chirality, Vacuum achiral toward boson photons is not exactly achiral toward fermion quarks (hadrons).

Phys. Rev. A 82, 043811 (2010)
http://pra.aps.org/abstract/PRA/v82/i4/e043811
http://physics.aps.org/pdf/10.1103/PhysRevA.82.043811.pdf

Chirality is a strong arrow of time (no external magnetic field is required),

Nature 463 210 (2010)
Phys. Rev. D 71 057501 (2005)
Phys Rev Lett. 91(24) 247404 (2003)
Chem. Phys. Lett. 173(5-6) 485 (1990)

If physics is incomplete at the postulate level, one universal solution can resolve its unlimited number of symmetry problems. Alas, it is testable in existing apparatus. Who would trust a theorist carrying a torsion pendulum?

24. The mathematician I had in mind (I only met him in his old age) was
http://en.wikipedia.org/wiki/Samuel_Eilenberg

but there must be many others like that.
By the way, concerning Hawking, I remember that many years ago, after meeting with Pope John Paul II, Hawking gave an interview in which he said something like this: 'The Pope said to me "whatever you do, do not undermine the Big Bang Theory." I did not want to tell him I that no longer believed in the Big Bang."
At that time I thought he was joking for the benefit of the journalists, but maybe there is one announcement still to be made.

25. What I dont get about this firewall business is that if the mass energy curve is asymptotic at c, how in the hell would matter stay together, and I also recall Susskind saying well nothing special would happen as one crosses the EH. Well dude, what about that asymptote? That has no physical meaning?