Stephen Hawking offers new resolution of black hole paradox

[marcus]

Bee Hossenfelder was live-blogging from Stockholm Conference on BH info puzzle today Tuesday 25 August.
Herewith:
http://backreaction.blogspot.com/2015/08/hawking-proposes-new-idea-for-how.html

The conference is 24-29 August. Hawking presented his idea Tuesday, based on joint work with Malcolm Perry (Cambridge) and Andy Strominger (Harvard). Perry also spoke today. According to the posted schedule for Tuesday, his talk was followed by talks by Carlo Rovelli and Francesca Vidotto.

The conference will include a range of different ideas for resolving the BH information paradox.
EDIT: videos of talk(s) may eventually appear at http://www.nordita.org/video/index.php?ev=hrad2015

 

[marcus]

Here's the press release about the conference from the Swedish host institution KTH:
https://www.kth.se/en/aktuellt/nyhe...-aim-at-paradox-of-black-hole-theory-1.585138

Here's the posted schedule of talks;
http://www.nordita.org/hawkingradiation/program/index.php
Here's the list of participants that was posted. I have highlighted the names of those scheduled to give talks:

• Stephen Hawking, University of Cambridge
• Jim Bardeen, University of Washington, Seattle
• Philip Candelas, University of Oxford
• Steve Christensen, UNIX Packages LLC
• Ulf Danielsson, Uppsala University
• Paul Davies, Arizona State University
• Fay Dowker, Imperial College London
• Michael Duff, Imperial College London
• Larry Ford, Tufts University
• Katie Freese, Nordita
• Steve Fulling, Texas A&M University
• Jim Hartle, University of California, Santa Barbara
• Gerard t’Hooft, Utrecht University
• Gary Horowitz, University of California, Santa Barbara
• Werner Israel, University of Victoria
• Claus Kiefer, University of Cologne
• Jorma Louko, University of Nottingham
• Laura Mersini-Houghton, University of North Carolina
• Charles Misner, University of Maryland
• Emil Mottola, Florida Atlantic University
• Jack Ng, University of North Carolina at Chapel Hill
• Jerome Novak, French National Centre for Science
• Don Page, University of Alberta
• Leonard Parker, University of Wisconsin, Milwaukee
• Malcolm Perry, Cambridge University
• Joe Polchinski, University of California, Santa Barbara
• Carlo Rovelli, Aix-Marseille University
• Philippe Spindel, University of Mons
• Kelly Stelle, Imperial College London
• Andy Strominger, Harvard University
• Bo Sundborg, Stockholm University
• Gerard 't Hooft, University of Utrecht
• Paulo Vargas Moniz, Universidade da Beira Interior
• Francesca Vidotto, Radboud University Nijmegen
• Bob Wald, University of Chicago

 

[martinbn]

I watched the video, but it is very brief. Can we see some of the details? He says that for the horizon of a stationary black hole one can define supertranslations in a similar way as for scri plus of an asymptotically flat space-time and they store the information of incoming particles. But how does it work, and what about evaporating black holes?

 

[marcus]

I watched the video, but it is very brief. Can we see some of the details? He says that for the horizon of a stationary black hole one can define supertranslations in a similar way as for scri plus of an asymptotically flat space-time and they store the information of incoming particles. But how does it work, and what about evaporating black holes?

We're told to expect a paper (from Hawking, Perry, Strominger) in September. I think what came out in Tuesday's talks by Hawking and, later, Perry was more of a teaser. Looking at Bee's blog for Tuesday I get the impression that she was left with a lot of questions. She made a brief reference to Perry's talk and said it cleared up some points.

I'd be more interested in hearing about some of the other talks at the conference. I'll post the program to give an idea, from the talk titles, of some of the other ways the BH enigma is being addressed. I don't think Hawking has a monopoly on interesting lines of investigation. Indeed it might be prudent to take the "supertranslations" gambit with a grain of salt.

Here's a condensed program (with lunches, coffeefbreaks, banquet etc deleted) just to give the titles of the talks by other participants:
MONDAY, 24 August
11.00 – 11.45 "Backreaction and Conformal Symmetry" G. 't Hooft
14.15 – 15.00 "Backreaction of Hawking Radiation and Singularities" L. Mersini-Houghton
16.00 – 16.45 "Physical interpretation of the semi-classical energy-momentum tensor in a Schwarzschild background" J. Bardeen
TUESDAY, 25 August
11.00 – 11.45 "The Information Paradox" S. Hawking
14.15 - 15.00 "Black Hole Memory" M. J. Perry
16.00 – 16.40 "Black to White Hole Tunnelling: Before or After Hawking Radiation?" C. Rovelli
16.40 – 17.10 "A new Quantum Black Hole Phenomenology" F. Vidotto
WEDNESDAY, 26 August
11.00 – 11.45 "Black Holes as Open Quantum Systems" C. Kiefer
14.15 - 15.00 "Particle Creation from vacuum in gravitational expansion and collapse" L. Parker
16.00 - 16.45 "Gravitational Condensate Stars or What's the (Quantum) Matter with Black Holes?" E. Mottola
THURSDAY, 27 August
11.00 – 11.45 "Did the chicken survive the firewall" J. Louko
14.15 – 15.00 "Gravity = (Yang-Mills)^2" M. Duff
16.00 – 16.45 "Black holes and other solutions in higher derivative gravity" K. Stelle
FRIDAY, 28 August
11.00 - 11.45 "Quantum Damping or Decoherence: Lessons from Molecules, Neutrinos, and Quantum Logic Devices" L. Stodolsky
14.15 – 15.00 "Puzzle Pieces: Do any fit?" Ch. Misner
16.00 – 16.45 "The Generalised Second Law and the unity of physics" F. Dowker
SATURDAY, 29 August
11.00 – 12.00 Group Discussion: Summary of Results and Open Questions
12.00 – 12.30 Status Report S. Hawking [TBC]
12.30 – 13.00 Conclusions P. Davies

 

[marcus]

We can check Bee's blog now and then for updates.
http://backreaction.blogspot.com
The latest update to the Tuesday post http://backreaction.blogspot.com/2015/08/hawking-proposes-new-idea-for-how.html was that another talk by Malcolm Perry had been scheduled for Wednesday (today) and that the plan was to record it and post the video at the Nordita website.
Presumably that would be here:
http://www.nordita.org/video/index.php
but I don't see it...

 

[anorlunda]

Isn't he just saying that Gerard t’Hooft, and Leonard Susskind were right all along, or is he saying something different, or am I oversimplifying?

 

[marcus]

't Hooft is at the conference and gave a talk Monday. What might he be saying about BH? Here's the most recent 't Hooft BH paper I could find:
http://arxiv.org/abs/0909.3426
Quantum gravity without space-time singularities or horizons
Gerard 't Hooft
(Submitted on 18 Sep 2009)
In an attempt to re-establish space-time as an essential frame for formulating quantum gravity - rather than an "emergent" one -, we find that exact invariance under scale transformations is an essential new ingredient for such a theory. Use is made of the principle of "black hole complementarity", the notion that observers entering a black hole describe its dynamics in a way that appears to be fundamentally different from the description by an outside observer. These differences can be boiled down to conformal transformations. If we add these to our set of symmetry transformations, black holes, space-time singularities, and horizons disappear, while causality and locality may survive as important principles for quantum gravity.
10 pages, 3 figures. Presented at the Erice Summerschool of Subnuclear Physics 2009

The title of his 2015 Stockholm talk "Backreaction and Conformal Symmetry" seems remarkably in line with this 2009 Erice paper! He may not have changed focus very much over the past 6 years, in his thinking about BH. I wish we had access to 't Hooft's talk.

A sample of Susskind's recent BH thinking:
http://arxiv.org/abs/1411.0690
Entanglement is not Enough
http://arxiv.org/abs/1403.5695
Addendum to Computational Complexity and Black Hole Horizons
http://arxiv.org/abs/1402.5674
Computational Complexity and Black Hole Horizons

Links possibly more relevant to what S.H. is talking about:
http://people.maths.ox.ac.uk/lmason/NGSA14/Slides/Arthur-Lipstein.pdf
http://iopscience.iop.org/1742-6596/283/1/012023/pdf/1742-6596_283_1_012023.pdf

 

[MTd2]

One of the people who led to this claim are some papers authored and co authored by an undergraduate 19 year old girl.

 

[RyanH42]

One of the people who led to this claim are some papers authored and co authored by an undergraduate 19 year old girl.

Who is she ?

 

[Strum]

Ugh nothing worse than these drama talks only ment to confuse people :|

 

[MathematicalPhysicist]

Bee Hossenfelder was live-blogging from Stockholm Conference on BH info puzzle today Tuesday 25 August.
Herewith:
http://backreaction.blogspot.com/2015/08/hawking-proposes-new-idea-for-how.html

The conference is 24-29 August. Hawking presented his idea Tuesday, based on joint work with Malcolm Perry (Cambridge) and Andy Strominger (Harvard). Perry also spoke today. According to the posted schedule for Tuesday, his talk was followed by talks by Carlo Rovelli and Francesca Vidotto.

The conference will include a range of different ideas for resolving the BH information paradox.

How do they plan to resolve the BH information paradox, is there any empirical experiment which is planned to resolve this paradox?

 

[marcus]

At least for the time being (in its present incomplete form) Hawking et al's proposal seems to have bombed. Bee writes:
http://backreaction.blogspot.com/2015/08/embrace-your-5th-dimension.html
==quote==
... Essentially he is claiming that our universe has holographic properties even though it has a positive cosmological constant, and that the horizon of a black hole also serves as a surface that contains all the information of what happens in the full space-time. This would mean in particular that the horizon of a black hole keeps track of what fell into the black hole, and so nothing is really forever lost.

This by itself isn’t a new idea. What is new in this work with Malcom Perry and Andrew Strominger is that they claim to have a way to store and release the information, in a dynamical situation. Details of how this is supposed to work however are so far not clear. By and large the scientific community has reacted with much skepticism, not to mention annoyance over the announcement of an immature idea.
==endquote==

 

[martinbn]

Why does she say that!? Presumably from discussions at the conference, but from the announcement it seems to me that they do not say that the event horizon contains all the information in the full space-time, but just the information for the matter that falls in.

 

[marcus]

A wide-audience wrap-up of the Hawking side of the conference, in SciAm:
http://www.scientificamerican.com/a...asn-t-solved-the-black-hole-paradox-just-yet/

It's unfortunate that no information is coming out about the other talks given at the conference. There were over a dozen other speakers on the program (including 't Hooft and several others well worth listening to) presenting other approaches to BH issues.
The organizers are missing an opportunity by not putting video online of talks like these and the ensuing discussion by the other participants:
"Backreaction and Conformal Symmetry" G. 't Hooft
"Puzzle Pieces: Do any fit?" Ch. Misner
"The Generalised Second Law and the unity of physics" F. Dowker

 

[marcus]

Why does she say that!? Presumably from discussions at the conference, but from the announcement it seems to me that they do not say that the event horizon contains all the information in the full space-time, but just the information for the matter that falls in.

Contains the information, as you say, and contains it classically, in the metric,which is somewhat surprising. IOW a BH has an enormous amount of hair, even at the classical level.

I suspect the HPS idea may be too half-baked to discuss at this point (but that's up to the expert participants to decide). To give an idea of possible reactions in the physics community:
==quote==
http://backreaction.blogspot.com/20...howComment=1440613730548#c6764159180892586245
transumante said...

The only clear thing is that none [of the audience] understood anything. Is this a new way of communicating scientific results? As a sybilline facebook status? Suspense, photographs, vague announcements? Why didn't they wait to submit the paper without any sensationalistic preview?

It is even more sad when renowned top scientists behave in this way.http://backreaction.blogspot.com/20...howComment=1440653755354#c5948626407447527793
transumante:

I can assure you that pretty much every one in the community thinks the same. Look, you shouldn't take Hawking as being representative for contemporary research. He is an extreme statistical outlier on all accounts. I have no idea why he wanted to announce his conclusion here and now. Maybe it was just because it was a good occasion and the timing seemed right, or because he likes Stockholm. It's certainly not something people commonly do. The standard procedure is, do the work, publish the paper, give the talks, and that's what the vast majority of physicists do. Every once in a while of course the timing goes wrong and somebody gives a talk about an almost-done work, or a yet-to-appear paper, and so on. Maybe it's a case like this, maybe the paper was supposed to appear earlier, but I don't know really.

B.
==endquote==

 

[Finny]

By and large the scientific community has reacted with much skepticism, not to mention annoyance over the announcement of an immature idea.

This could mean it is groundbreaking.

When was the last time a great breakthru was widely and wildly 'accepted'?? It wasn't GR.

 

[MTd2]

Who is she ?

http://arxiv.org/find/hep-th/1/au:+Pasterski_S/0/1/0/all/0/1

 

[MTd2]

By and large the scientific community has reacted with much skepticism, not to mention annoyance over the announcement of an immature idea.

I think for Stephen Hawking is a different thing. He looked so fragile on his presentation. He was manipulating his computer with a move detector attached to his glasses, which read tiny movements of the right of his lips and eyebrows.

I think he was trying to take to make the best of his time to at least share his ideas (this one specifically was only 1 month old at the day of the presentation).

 

[marcus]

http://arxiv.org/find/hep-th/1/au:+Pasterski_S/0/1/0/all/0/1

Sabrina Gonzalez Pasterski
is listed as 22 years old in a July 2015 article about her. But earlier this year when she was written up, she was 21.
I understand she is a first generation Cuban-American raised in Chicago. Her parents would have emigrated from Cuba.
Chicago has a regional school for the gifted, she went to MIT for undergrad and IIRC graduated at the top of her class, or something amazing like that. She has done a lot of remarkable things like build and fly her own experimental aircraft. So as a 21 year old she was in the PhD program at Harvard, collaborating with Strominger and others on papers like this:
http://arxiv.org/abs/1502.07644
Higher-Dimensional Supertranslations and Weinberg's Soft Graviton Theorem
Daniel Kapec, Vyacheslav Lysov, Sabrina Pasterski, Andrew Strominger
(Submitted on 26 Feb 2015)
Asymptotic symmetries of theories with gravity in d=2m+2 spacetime dimensions are reconsidered for m>1 in light of recent results concerning d=4 BMS symmetries. Weinberg's soft graviton theorem in 2m+2 dimensions is re-expressed as a Ward identity for the gravitational S-matrix. The corresponding asymptotic symmetries are identified with 2m+2-dimensional supertranslations. An alternate derivation of these asymptotic symmetries as diffeomorphisms which preserve finite-energy boundary conditions at null infinity and act non-trivially on physical data is given. Our results differ from those of previous analyses whose stronger boundary conditions precluded supertranslations for d>4. We find for all even d that supertranslation symmetry is spontaneously broken in the conventional vacuum and identify soft gravitons as the corresponding Goldstone bosons.
24 pages

She also collaborated with Strominger and friends on some less explicitly related papers in 2014.

 

[MTd2]

Recently, Raphael Bousso came up with 2 breakthroughs in GR and holography:

http://arxiv.org/abs/1506.02669
http://arxiv.org/abs/1504.07660

His PhD adviser was Stephen Hawking.

I really like theories whose fundamentals and basic forms can be explored and expressed with high ratio of ideas/(math expressions).

 

[marcus]

...

http://arxiv.org/abs/1506.02669
http://arxiv.org/abs/1504.07660

His PhD adviser was Stephen Hawking.

I really like theories whose fundamentals and basic forms can be explored and expressed with high ratio of ideas/(math expressions).

I understand, but we are getting very far from the topic of the thread. I do not see that those two Bousso papers have anything at all to do with BH info paradox in general or with Hawking's idea in particular. At least in the case of Sabrina Pasterski, she co-authored a paper with Strominger on supertranslations earlier this year, and Hawking's proposal which involves supertranslations is actually the work of three people Hawking-Perry-Strominger.

http://backreaction.blogspot.com/2015/08/hawking-proposes-new-idea-for-how.html

 

[Physics Monkey]

It looks to me like http://arxiv.org/abs/1508.06577 by R. Penna, which just appeared last night, is a very closely related proposal.

BMS invariance and the membrane paradigm
Robert F. Penna
(Submitted on 26 Aug 2015)
We reinterpret the BMS invariance of gravitational scattering using the membrane paradigm. BMS symmetries imply an infinite number of conserved quantities. Energy conservation at every angle is equivalent to the fluid energy equation on the membrane (a conservation law at each point in the fluid). Momentum conservation at every angle is equivalent to the Damour-Navier-Stokes equation on the membrane. Soft gravitons are encoded in the membrane's mass-energy density, Σ(z,z¯). Fluid dynamics is governed by infinite dimensional reparametrization invariance, which corresponds to the group of volume preserving diffeomorphisms. This coincides with the generalized BMS group, so there is a connection between the fluid and gravity pictures at the level of symmetries. The existence of membrane fluid conservation laws at event horizons implies BMS symmetries also act on event horizons. This may be relevant for the information problem because it implies infalling information can be stored in Σ(z,z¯) at the horizon. The teleological nature of the membrane at the horizon may be related to the black hole final state proposal.

 

[Spinnor]

http://arxiv.org/find/hep-th/1/au:+Pasterski_S/0/1/0/all/0/1

From

https://www.google.com/search?safe=....1.1.0...0...1c.1.64.serp..0.1.86.sHZ9GL0qVMY

 

[MTd2]

I do not see that those two Bousso papers have anything at all to do with BH info paradox in general or with Hawking's idea in particular.

It's about the "Essentially he is claiming that our universe has holographic properties even though it has a positive cosmological constant, and that the horizon of a black hole also serves as a surface that contains all the information of what happens in the full space-time." http://backreaction.blogspot.com.br/

 

[Finny]

At least for the time being (in its present incomplete form) Hawking et al's proposal seems to have bombed. Bee writes:

"Hawking presented his idea Tuesday, based on joint work with Malcolm Perry (Cambridge) and Andy Strominger (Harvard)."

Seems a rather formidable trio be dismissing?

 

[Haelfix]

Hawking has been dismissed most of his career upon the first presentations of a new idea. Historically it has usually been a great mistake to do this, b/c more often than not he has been deeply in advance of his detractors and the ideas usually have much more oomph to them than it might naively seem.

His situation is such that it is very difficult for him to actually flush out an idea, or to have quantitative arguments about nitty gritty details. Instead he is blessed with very acute mental pictures of what takes place, and it's difficult for him to explain how this works in great detail. This unfortunate aspect gives his presentations a bit of an oracle quality and hence much of the crazy press.

This is usually a matter of great frustration within the community, especially since his ideas here (and those back in the mid2ks) are not necessarily new to people. The asymptotic symmetry group aspect of GR has been a very fruitful avenue of research since the early 80s and was a precursor foundation to Brown-Henneaux's work and ultimately to AdS/CFT. Many people have been following Stromingers work on this subject for the last few years. Likewise the business about decoding the hologram is one of the very central textbook aspects of the information paradox, and is well studied.

So of course we would like to know the details..

 

[Ben Niehoff]

Indeed, everything he says has a tendency to require quite a bit of unpacking. It will be interesting to see the finished paper. I don't think that Malcolm or Andy intend to make any claims that are not supported by calculations.

 

[MTd2]

Infinite symmetries, that is infinite charges conserved. I wonder if they can be use to regularize perturbatively GR.

 

[Richardx]

It seems to me that Hawking has pointed out something that should have been pretty obvious: if, from an outside observer’s viewpoint, infalling material appears to stop at the event horizon, then from the standpoint of everything outside the black hole, the material is stuck on the event horizon, so its ‘information’ is not lost, and the event horizon is not black at all, but a (colorful?) record of everything that has hit it. My question is: what happens as the event horizon expands?

 

[Berlin]

The expansion created more horizon surface to store the extra information I would guess...

 

[marcus]

... ‘information’ is not lost, and the event horizon is not black at all, but a (colorful?) record of everything that has hit it. My question is: what happens as the event horizon expands?

The expansion created more horizon surface to store the extra information I would guess...

According to the usual story, the event horizon shrinks as the BH evaporates. And eventually the horizon disappears in a final burst of H. radiation.
So it does seem that you need to refine your question: what happens as the event horizon contracts?
The information must somehow get off the event horizon and save itself by taking flight (either in the H. radiation, or encoded as variations in the gravitational field, or?)

That is, at least if it is meaningful for unitarity to be treated as an absolute requirement for all time.

 

[Chronos]

I think Hawking is ill and hoping to make a splash while he is still able to communicate.

 

[Ben Niehoff]

I think Hawking is ill and hoping to make a splash while he is still able to communicate.

What a terrible thing to say.

 

[Physics Monkey]

http://www.latimes.com/science/scie...-hole-information-paradox-20150826-story.html in the LA Times is enlightening. There are a few salient quotes from Strominger at the end of the article.

 

[marcus]

PM thanks for the link to those salient quotes from Strominger! They are worth excerpting:
==quote LA Times==
Contacted via telephone on Tuesday evening, Strominger said he felt confident that the information loss paradox was not irreconcilable. But he didn't think everything was settled just yet.

He had heard Hawking say there'd be a paper by the end of September. It had been the first he'd learned of it, he laughed, though he said the group did have a draft.

Whatever the team publishes, Strominger added, it's unlikely to be the final word.
==endquote==

The quote from Polchinski was also sobering:
==quote LA Times==
UC Santa Barbara physicist Joseph Polchinski, who has thought about the problem a great deal in the past, said that he, too would need to see Hawking's calculations to understand if the solution made sense.

"I don't think what Hawking and his collaborators are proposing is radical enough to solve the problem," he said. "But I haven't seen the publication, so I'm just speculating."
=endquote==

I thought the LA Times reporter did a good bit of journalism. It was smart to contact John Preskill at Caltech, and to talk with Strominger directly.
Here are a few more remarks from Strominger:
==quote LA Times==
"There's still much more work to be done to show that when something falls into a black hole that it leaves a record of exactly what it was. That is the part we still need to work out," he said. "Stephen is very optimistic that it's all going to work perfectly. But physics is a hard mistress. You have to get all the calculations to work perfectly and everything has to line up."

"Stephen is a smart guy," Strominger continued. "Maybe he's seeing all the way to the end. I'm certainly not."
==endquote==
http://www.latimes.com/science/scie...-hole-information-paradox-20150826-story.html

 

[Garth]

Would information be preserved through a 'Big Crunch' of a cyclical universe?

If so the entropy problem reappears.

Garth

 

[Ben Niehoff]

The conference participants have all sat down together to do a Reddit AMA. Might be entertaining to read:

https://www.reddit.com/r/IAmA/comments/3iuf6c/we_are_the_international_group_of_theoretical/

 

[marcus]

The conference participants have all sat down together to do a Reddit AMA. Might be entertaining to read:

https://www.reddit.com/r/IAmA/comments/3iuf6c/we_are_the_international_group_of_theoretical/

Great! Thanks for posting the link!
Here's a brief sample of discussion
https://www.reddit.com/r/IAmA/comments/3iuf6c/we_are_the_international_group_of_theoretical/cujq1qu
Francesca was active in Physicsforums for several years, and still occasionally drops in. She gave a talk at the the Stockholm conference and also participated in the Reddit later.
https://www.reddit.com/r/IAmA/comments/3iuf6c/we_are_the_international_group_of_theoretical/cujq8hr
Here's a very brief thread where both Carlo Rovelli and Malcolm Perry replied to a question about "super translations"
https://www.reddit.com/r/IAmA/comments/3iuf6c/we_are_the_international_group_of_theoretical/cujporr

==sample quote from Carlo and Malcolm==
CarloRovelli 12 points 2 days ago

Here is a zero-level version of what a "super translation" means. Take a big sphere and imagine many clocks on it, say all beating at the same time. Now make one of the cocks miss a bit. So now that particular clock is a bit later than all the others. Well, this change is (an elementary version of) a "super translation". It is a "translation" because it is like "translating in time". But it is a "super" translation because it does not translate all the clocks (like normal time translation would), but only some of them. Now it turns out out, or at least so suggest Malcolm and Stephen, that the "super translations" might code the information about how things fall in a black hole... but Malcolm can certainly explain this part better...

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MalcolmJPerryPHYSICIST 14 points 2 days ago

The original idea of a super translation relates to how to detect gravitational radiation. Imagine a collection of satellites orbiting the earth. As you look into the sky, these satellites will formake a fixed pattern. Now suppose that a burst of gravitational radiation passes through the system. The pattern the satellites makes will change. The mathematical description for this change is called a super translation. What is new is the discovery that can extend the idea of a super translation to the horizon of a black hole. Then the super translation will give information about what has fallen into a black hole. In this way, one can determine what goes to make up the black hole and hence resolve (or perhaps help to resolve) the black hole information paradox

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==endquote==

 

[marcus]

Would information be preserved through a 'Big Crunch' of a cyclical universe?

If so the entropy problem reappears.

Garth

I'm not sure that bounce cosmologies have an entropy problem, Garth, because entropy is observer-dependent. The observer's coarse grain map of what matters--what makes a difference and what doesn't. We depend on the fact that according to our coarse-graining map the entropy was very low at the bounce, or start of expansion.

But in a bounce cosmology, at the bounce itself there are no observers, so entropy is simply not definable. The observers are partitioned into two groups, those before and those after.

I don't speculate about "cyclic". That is a further topic of conversation. Just a simple one-bounce model cosmology as in the paper by Ed Wilson-Ewing and Yi-Fu Cai

 

[Ben Niehoff]

Here is Malcolm's talk, and I suspect Nordita has put up everyone else's talk as well:

 

[marcus]

Ben, I suspect Nordita will post the other talks as you suggest. At http://www.nordita.org/video/index.php
they have batches of talks from other events like this conference, and they have added an icon for this conference on that page.
So far when you click on it you get a menu with only 1 talk, Malcolm Perry's:
http://www.nordita.org/video/index.php?ev=hrad2015

But it is clearly set up to have videos of the other talks from the event added to the menu. We can check the menu later in the week and see what they have added to it.

 

[Ben Niehoff]

By the way, I'm impressed at the production value of Nordita's talk videos (at least Malcolm's above). Three different camera angles! I don't think most conferences do this. I only remember seeing one camera in the room at any conference I've attended.

 

[marcus]

Hawking now has a 3 page paper on arxiv covering his talk and giving references
http://arxiv.org/abs/1509.01147
The Information Paradox for Black Holes
S. W. Hawking
(Submitted on 3 Sep 2015)
I propose that the information loss paradox can be resolved by considering the supertranslation of the horizon caused by the ingoing particles. Information can be recovered in principle, but it is lost for all practical purposes.
3 pages. Talk given on 28 August 2015 at Hawking Radiation, a conference held at KTH Royal Institute of Technology, Stockholm

It's quite brief, the abstract (which you see here) plus 1 and 1/2 page of text, plus half a page of references.
I think basically just a verbatim transcript of the talk, which we have recorded on video. But it's nice to see specific references.

 

[0-fmg]

Inside a black hole there is gravity, matter and energy. The event horizon of a black hole is the limit between the black hole and the space. When the matter reaches the event horizon it turns into energy. E=mc2.

 

[anorlunda]

Hawking now has a 3 page paper on arxiv covering his talk and giving references
http://arxiv.org/abs/1509.01147
The Information Paradox for Black Holes
S. W. Hawking
(Submitted on 3 Sep 2015)
I propose that the information loss paradox can be resolved by considering the supertranslation of the horizon caused by the ingoing particles. Information can be recovered in principle, but it is lost for all practical purposes.
3 pages. Talk given on 28 August 2015 at Hawking Radiation, a conference held at KTH Royal Institute of Technology, Stockholm

It's quite brief, the abstract (which you see here) plus 1 and 1/2 page of text, plus half a page of references.
I think basically just a verbatim transcript of the talk, which we have recorded on video. But it's nice to see specific references.l

I read that paper, but I don't understand the premise. Hawking's approach is to analyze what happens when a particle falls in through the EH. But that does not address the information paradox with respect to mass trapped inside the BH as the star collapsed and which, therefore, never did pass through the EH.

My understanding of information conservation is that it is strict. Unless the paradox is resolved for every last particle, it remains a paradox.
Is that correct?