206. A conference on black holes at PI
ASTRO, HEP-TH/PH — By Dmitry Podolsky on January 27, 2009 at 7:05 pm
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A very interesting conference organized by Rob Meyers, Herman Verlinde and Jaume Gomis takes place currently in PI. The topic of the conference is related to information loss in black holes and unitarity of quantum gravity in general (the one that I tried to discuss so unsuccessfully on the blog in December – I am a kind of being better prepared now 
).
Although it seems to be impossible to listen talks in real time (and therefore – to ask speakers in real time, which the system implemented in PI allows to do in principle), they do appear on PIRSA with delay about 2 days. Currently, the following presentations are accessible:
(Update. Lubos Motl commented on almost any talk, and I think it is worth to add his comments into the text of the post itself (they will be denoted LM))
- Ten theses on black hole entropy by Raphael Sorkin. He tries to relate black hole entropy to “horizon degrees of freedom”. The entropy is finite because the fine stricture of spacetime is descrete (hmm).
LM: Sorkin discovered the Kaluza-Klein monopoles, which are cool, among other things. It makes it more disappointing to see him saying all this superficial nonsense – things must be discrete because entropy is finite (WTF?) and evolution must be even non-unitary because of the second law (WTF?).
- Unitarity and holography in gravitational physics by Donald Marolf. Since, he says, gravitational hamiltonian is zero and the surface Gibbons-Hawking term drives the dynamics, information is stored differently in quantum gravity than it is stored in local quantum field theories. Depending on the boundary conditions you choose different behavior of information is possible. If you choose AdS boundary conditions, then the unitarity holds (boundary observables are independent of time). If you choose asymptotically flat boudary conditions, then “perturbative holography” holds as he call it: algebra of observables at
within neighborhood of 
contains all perturbative observables. I am not sure what it exactly means
LM: Marolf is interesting. He links the boundary-term-only character of the GR Hamiltonian to holography. He also identifies the correct boundaries – spacetime-like for AdS and null for flat. Well, the on-shell scattering matrix in flat space is what replaces the AdS holography. I agree with that but not sure what more to learn about it. I am completely puzzled by the theories that are ?consistent both with AdS/CFT and LQG? etc. They must surely be completely tautological and uninteresting if they?re consistent with everything.
- Black holes, fundamental destruction of information and conservation laws by Jonathan Oppenheim. He says that information loss and decoherence is related to the violation of conservation laws or non-locality and tries to invent a theory which supports a generalization of Noether currents and is local, but still information can be lost.
LM: Oppenheim. OK, let me skip that. If I understand well, he wants to violate a maximum number of conservation laws, destroy information, destroy locality, misinterpret decoherence, and do everything else incorrectly, too. Real QG depends on tight approximate or exact validity of all these things he completely sacrifices.
- Resolving the information loss paradox by Samir Mathur. As you may expect, he discusses his fuzzball proposal.
LM: Mathur. I?ve dedicated a lot of time recently to fuzzballs so I suppose he will review it, and probably agree with de Boer, Vijay et al., and give some of their examples.
- Matrix models for the black hole information paradox by Takuya Okuda. He discusses toy models for eternal black holes in AdS spacetime by means of AdS/CFT. His large N models exhibit late time fall-off of a two-point function and this effect persists even if quantum gravity corrections are taken into account (so, the main conclusion is that information loss is there contrary to what you might expect from the usual AdS/CFT lore).
LM: Okuda. He was around at Harvard. Very sharp picture. He wrote the paper with Polchinski that to all orders in 1/N, the information is lost, so the preservation is nonperturbative in 1/N in Matrix models e.g. nonpert. in Gnewton. I don?t expect him to say anything qualitatively different here, perhaps in a different model. Sumir?s comments here look kind of elementary & morally wrong to me. Jesus Christ, I can?t believe he says all the stuff, and thanks God that Simeon Hellerman is there. Plus a lot of nonsense from Jacobson, and another nonsense with baby universe. I don?t have patience for these multicultural gatherings that end in complete chaos.
- Schwarzschild radius and black hole thermodynamics with
corrections from simulations of SUSY matrix quantum mechanics by Jun Nishimura.He discusses his Monte Carlo simulations of SUSY matrix quantum mechanics at finite temperature. The goal is to fit it with black hole on AdS via AdS/CFT and be able to include corrections.
LM: Nishimura – impressive D0-brane simulations. I?ve heard on it a bit, and worked on similar projects recently, but don?t want to watch it now.
- Black holes as mirrors by Patrick Hayden. Discussing cond-mat analogies of black hole evaporates, he is mainly interested in dynamics of Hawking evapouration. For example, he claims that if the evaporation of the black hole has already proceeded past the half-way, additional quantum information deposited in the black hole is revealed in the Hawking radiation very rapidly.
LM: Hayden works with Preskill and I find these results amazing, but this presentation or maybe this result is just confusing. When I wrote about it, it made sense but now it doesn?t. He can only get ?delta S? of information where ?S? is the change of the BH entropy, and the information from a couple of Hawking quanta is a mixed function of some old info about the BH microstate and the newly infell matter. I can?t possibly see how they could get more than this complicated function – the numbers directly – by quantum error corrections. Oh, I see, they also have all the information from the Hawking radiation that came out before that. Understood.
- The Kerr/CFT Correspondence by Thomas Hartman. Since astrophysical black holes are non-SUSY, not charged and live in 4d, he says, AdS/CFT cannot be really applied to them. However, it is possible to show that these (extremal) black holes are still dual to CFT, and he discusses this CFT.
LM: Kerr/CFT. Well, I know this too well, having seen an exrta talk by Monica in Prague in December etc. So I won?t watch Tom, I am sure he was great, too. It is a cool result here.
- Black Holes as Fast Scramblers by Yasuhiro Sekino. He discusses his recent paper with Susskind. The idea is that BHs “thermalize” information in the most rapid possible way in Nature.
LM: Sekino, scramblers with Susskind. It?s a cool result. I am sure that BHs are the most chaotic, fastest thermalizers.
- On energy extraction from rotating black holes by Herman Verlinde. Herman explains how the Mankind can solve its energy problems for many decades to come
LM: Herman seems to follow Penrose.
Steven Chu should watch it. I find it better to create smaller black holes that evaporate and get all the 
matter out of it, assuming B is not conserved. Rotating holes are too simple and classical. I assume it is a classical talk.
If you are a newcomer into the subject of information loss (like I am), a very good introductionary book which may help a lot is the one by Susskind and Lindesay.
17 Comments
1. Sorkin discovered the Kaluza-Klein monopoles, which are cool, among other things. It makes it more disappointing to see him saying all this superficial nonsense – things must be discrete because entropy is finite (WTF?) and evolution must be even non-unitary because of the second law (WTF?).
2. Marolf is interesting. He links the boundary-term-only character of the GR Hamiltonian to holography. He also identifies the correct boundaries – spacetime-like for AdS and null for flat. Well, the on-shell scattering matrix in flat space is what replaces the AdS holography. I agree with that but not sure what more to learn about it. I am completely puzzled by the theories that are “consistent both with AdS/CFT and LQG” etc. They must surely be completely tautological and uninteresting if they’re consistent with everything.
3. Oppenheim. OK, let me skip that. If I understand well, he wants to violate a maximum number of conservation laws, destroy information, destroy locality, misinterpret decoherence, and do everything else incorrectly, too. Real QG depends on tight approximate or exact validity of all these things he completely sacrifices.
4. Mathur. I’ve dedicated a lot of time recently to fuzzballs so I suppose he will review it, and probably agree with de Boer, Vijay et al., and give some of their examples.
5. Okuda. He was around at Harvard. Very sharp picture. He wrote the paper with Polchinski that to all orders in 1/N, the information is lost, so the preservation is nonperturbative in 1/N in Matrix models e.g. nonpert. in Gnewton. I don’t expect him to say anything qualitatively different here, perhaps in a different model. Sumir’s comments here look kind of elementary & morally wrong to me. Jesus Christ, I can’t believe he says all the stuff, and thanks God that Simeon Hellerman is there. Plus a lot of nonsense from Jacobson, and another nonsense with baby universe. I don’t have patience for these multicultural gatherings that end in complete chaos.
6. Nishimura – impressive D0-brane simulations. I’ve heard on it a bit, and worked on similar projects recently, but don’t want to watch it now.
7. Hayden works with Preskill and I find these results amazing, but this presentation or maybe this result is just confusing. When I wrote about it, it made sense but now it doesn’t. He can only get “delta S” of information where “S” is the change of the BH entropy, and the information from a couple of Hawking quanta is a mixed function of some old info about the BH microstate and the newly infell matter. I can’t possibly see how they could get more than this complicated function – the numbers directly – by quantum error corrections. Oh, I see, they also have all the information from the Hawking radiation that came out before that. Understood.
8. Kerr/CFT. Well, I know this too well, having seen an exrta talk by Monica in Prague in December etc. So I won’t watch Tom, I am sure he was great, too. It is a cool result here.
9. Sekino, scramblers with Susskind. It’s a cool result. I am sure that BHs are the most chaotic, fastest thermalizers.
10. Herman seems to follow Penrose.
Steven Chu should watch it. I find it better to create smaller black holes that evaporate and get all the E=mc2 matter out of it, assuming B is not conserved. Rotating holes are too simple and classical. I assume it is a classical talk.
Dear Lubos,
Wow, that was very useful. Do you mind if I add your comments in the text of the post?
Cheers,
Dmitry.
Dear Dmitry,
I’m sorry if I sound like a “party-pooper”, but the entire business of black hole physics and the information loss paradox appears to be plagued with too many ad-hoc propositions and unverifiable claims. If you patiently read all the PI presentations (and also refer to Sabine’s Backreaction blog), you get a sense of utter confusion. Do we truly believe that the physics of black holes is more transparent now or are we just fooling ourselves with wishful thinking?…
Regards,
Ervin
Dear Ervin,
so what? information loss is an open question – like confinement. It is a technically hard problem to resolve – like confinement. It is unclear what happens even at the conceptual level – maybe unlike confinement, but then, who knows – maybe, the nature of the latter is misunderstood (say, it has nothing to do with dual Meissner effect, simply because there are no monopoles in confining asymptotically free gluodynamics). But this just makes the information loss problem in a sense even more exciting than confinement, doesn’t it?
Cheers,
Dmitry.
Dear Dmitry,
The difference that I see between the information loss paradox in black hole (BH) physics and confinement in gluodynamics is that the latter is backed up by plenty of observational evidence. For instance, as explained to me by Sabine Hossenfelder, astrophysical data alone cannot settle the issue of where the BH entropy is coming from. How can one realistically hope to solve this paradox without having a sound connection to testing data?
Cheers,
Ervin
Dear Ervin,
Ok, agree, they are somewhat different in this respect. Would you say the same to Albert Einstein in 1905 or, even better, around 1915?
Cheers,
Dmitry.
Dear Dmitry,
Einstein was always skeptical of General Relativity before 1919 when gravitational bending of light was confirmed. He was a notoriously humble scientist, ready to accept that his theories can be failed by Nature. He admitted “the biggest blunder of his life” (cosmological constant) with no hesitation whatsoever.
With all due respect to many of our contemporary colleagues, this level of humility and respect for objective evidence is long gone…
Cheers,
Ervin
Dear Ervin,
Could you prove the statement?
A link to a Einstein’s biographer with rather high level of authority will do.
This example does not really help you and shows instead that the higher or lower level of humility alone(unfortunaltely) does not make a person being right
Anyway, what I really asked is the following: a person A came out with the theory of everything (well, general relativity) which is currently impossible to check on experiment. The person A actually wants to publish his theory. Would you ask the person A to back off?
Cheers,
Dmitry.
Dear Dmitry,
One of the most authoritative biographies on Einstein is “Subtle is the Lord…” by Abraham Pais, Oxford University Press, 1982. Regarding Einstein’s struggles with General Relativity prior to 1916 and up to 1919, refer to the Introduction as well as to chapters 11 to 13.
Cheers,
Ervin
Dear Ervin,
Thanks! I was also thinking of Pais’ book but was damn sure that Pais did not say anything like this. I guess I was wrong.
Cheers,
Dmitry.
Dear Dmitry,
Let me clarify my point: I am not advocating censoring someone just because there is no experimental evidence available yet to prove or falsify his/her theory. But I would have an issue if his/her theory is UNTESTABLE, which seems to be case with the information paradox and the nature of entropy in BH physics.
The remarks about Einstein (sadly) reflect on the fact that there are too many scientists nowadays that disingenuously promote their ideas through TV and internet, before being backed up by real testing data.
Feel free to disagree…it is just a personal opinion, that’s all.
Regards,
Ervin
Dear Ervin,
Ok, fair enough. However, I doubt that BH related staff is really that untestable. First of all, through AdS/CFT you can really have an idea what happens with BHs simply working on the field theory side. Second, there are some nice analogies between gravitational physics and hydrodynamics (one may take a look on papers by Volovik for example, on Painleve-Gullstrand BH).
But to me, both of the analogies above are secondary. What’s more important is the fact that particles are produced in strong fields. This one is experimentally established (Schwinger pair production). If you accept that gravitational field is like any other field (will you really doubt that?), then particles are also produced in a strong gravitational field for sure.
Black holes are just an example of the situation where the gravitational field can be considered strong enough to produce pairs (that is, Hawking radiation). Note also that you don’t really need GR to predict black holes and many of their properties, qualitatively, their physics can be understood already at the level of Newtonian gravitation.
Finally, if you accept Hawking radiation, BH entropy comes out automatically.
Cheers,
Dmitry.
Dear Dmitry,
“Finally, if you accept Hawking radiation, BH entropy comes out automatically”
Could you please do me a favor and look up the comments section for this posting at the “Backreaction” blog?:
https://www.blogger.com/comment.g?blogID=22973357&postID=7422162679290376585
The title of this posting is “Conservative solutions to the black hole information problem”. It refers to one of the PI presentations by Sabine Hossenfelder. Now put yourself in the shoes of a fresh graduate student that wishes to learn about the topic of BH entropy and opens this reliable blog with an open mind. Tell me what you honestly think after reading the 168+ comments. Do you still believe that the student can leave with a crystal clear understanding?
Cheers,
Ervin
Dear Ervin,
Would I be a graduate student, I wouldn’t certainly acquire a clear understanding after reading Sabina Hossenfelder’s blog. What would be good to do in this case? I think that I would actually look for a source with higher level of authority (which is in this particular case not terribly hard to find) – for example, for a good basic level book with introduction into the subject (like Susskind, Lindesay). I would also realize that finding a higher authority source of information would actually save me hours of time.
Cheers,
Dmitry.
Dear Dmitry,
Your conclusion reinforces my comment of January 29th: the majority of PI presentations have unfortunately led to confusion and an endless debate. It appears that the talks contain too many ad-hoc propositions and unverifiable claims.
Cheers,
Ervin
Dear Ervin,
I don’t see how. First, only two PI presentations have led to a big confusion and endless debate on Hossenfleder’s blog (you can guess which ones). Second, there is a good reason for Sabina to make this debate endless in order for confusion to grow. Finally, if all participating in the endless debate would have read the book I mentioned, the level of confusion would dramatically decrease (as well as the number of comments, of course).
Cheers,
Dmitry.
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