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Holey War's far from over

  1. Aug 1, 2008 #1

    marcus

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    http://www.nature.com/nature/journal/v454/n7204/full/454579a.html

    this is Nature mag's teaser. they give you some of Paul Davies book review of Black Hole Wars and then say if you want to continue reading this, pay $32.

    So here is a sample from their teaser:

    ==quote from Davies in Nature==
    The momentous conclusion that a black hole swallows and permanently obliterates physical information didn't bother Hawking, whose background was in gravitational theory and space-time geometry rather than particle and quantum physics. With theorist Roger Penrose of the University of Oxford, UK, he proved that space and time could have boundaries or edges, called singularities, at which information might enter or leave the Universe. The general theory of relativity predicts that such a singularity lurks at the centre of a black hole, where the gravitational field and space-time warp become infinite. As a consequence, the imploding star's information might disappear from space and time through the hole's singularity. Hawking was sufficiently confident to place a bet with theoretical physicist John Preskill at the California Institute of Technology in Pasadena...


    Is the matter laid to rest? I don't think so.
    Hawking justified his reversal by sketching out a calculation, but quantum gravity is still too unrefined for a rigorous proof. The weak point is that, in quantum gravity, the singularity can be replaced by a space-time region with a complicated and changing topology, allowing information to shift from one region of space-time into another disconnected one, perhaps from our Universe to a newly born 'baby universe'. Susskind dismisses this possibility, but the matter is far from resolved. It may be that if we consider the entire 'meta-verse' of all spatial regions, information is never lost. But if we restrict attention to a single universe, or connected region of space, then information can in fact leak out. Deciding the matter is a task for a future generation of theoretical physicists.

    To read this story in full you will need to login or make a payment...

    ==endquote==
     
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  3. Aug 1, 2008 #2

    marcus

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    OK as Davies says deciding the matter is a job for future generation physicists. and here are two future generation physicists Christian Boehmer and Kevin Vandersloot who have been tackling the job and working on it.

    They found that using the LQG model there is no BH singularity. What replaces the BH pit singularity, in the LQG context, they found to be a NARIAI-type universe. this is a welldefined type of universe first described by a guy in Japan named Nariai. Wikipedia has some stuff about it.

    Some people think the Nariai universe is unstable and something might cause it to blow up into our kind of universe. Expansion could spread out into all three spatial dimensions instead of remaining concentrated in one.

    Boehmer and Vandersloot argue that it will not. They say the Nariai universe that develops from the former pit singularity is stable. We will see.

    Anyway the wheel's still in spin regarding where the information goes that falls into a BH.
    A lot has been written this year and last---this Boehmer Vandersloot is just a taste of it:

    http://arxiv.org/abs/0709.2129
    Loop Quantum Dynamics of the Schwarzschild Interior
    Christian G. Boehmer, Kevin Vandersloot
    published in Physical Review D 76 (2007) 104030
    (Submitted on 13 Sep 2007)

    "We examine the Schwarzschild interior of a black hole, incorporating quantum gravitational modifications due to loop quantum gravity. We consider an improved loop quantization using techniques that have proven successful in loop quantum cosmology. The central Schwarzschild singularity is resolved and the implications for the fate of an in-falling test particle in the interior region is discussed. The singularity is replaced by a Nariai type Universe. We discuss the resulting conformal diagram, providing a clear geometrical interpretation of the quantum effects."

    http://arxiv.org/abs/0807.3042
    Stability of the Schwarzschild Interior in Loop Quantum Gravity
    Christian G. Boehmer, Kevin Vandersloot
    4 pages, 4 figures
    (Submitted on 18 Jul 2008)

    "In recent work, the Schwarzschild interior of a black hole was investigated, incorporating quantum gravitational modifications due to loop quantum gravity. The central Schwarzschild singularity was shown to be replaced by a Nariai type universe. In this brief report we show that this interior solution is stable with respect to small perturbations, in contrast to the classical Nariai universe."

    =====================
    Kevin Vandersloot is an Ashtekar PhD (2006?) now postdoc at Portsmouth, ESF Marie Curie fellow.
    Christian Boehmer is at University College London. I think he is from Berlin---2003 Diplomarbeit at Max Planck Potsdam (AEI).
    I don't know anything about him, would guess his PhD is from about the same time (2006?) as Kevin's
    This is why I tend to think of them as second generation quantum gravity research.

    A Nariai universe is not what anyone would have chosen.
     
    Last edited: Aug 1, 2008
  4. Aug 1, 2008 #3

    George Jones

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    What is the last sentence that you see? Is it
    If so, then the only thing $32 is
     
  5. Aug 1, 2008 #4

    marcus

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    Excellent! So this time the teaser actually includes the whole article! And yet they still invite us to pay #32 to get the whole article. It doesn't make sense but it's how it is.
    Thanks for letting us know.
     
  6. Aug 1, 2008 #5
    You do not need to pay the $32. The Preskill-Hawking bet is well documented on the internet (See http://www.google.co.uk/search?hl=en&safe=active&q=Preskill+hawking+bet&btnG=Search&meta= ) and hawking concedes he lost his bet that "Information can be lost forever in black holes" (possibly into other universes).

    In this article http://news.bbc.co.uk/1/hi/sci/tech/3913145.stm Hawking is quoted as saying "The black hole only appears to form but later opens up and releases information about what fell in, so we can be sure of the past and we can predict the future." (My emphasis) I wonder what hawking really meant by that last statement? It seams to agree with my personal (non conventional) view that blackholes of the type that have a singularity of infinite density never actually form in a finite time scale and that black holes are actually a hollow shell of matter asymptotically aproaching the event horizon. However the statement is somewhat anbiguous and can be interpreted a number of ways.

    Hawking outlined his new idea on blackhole's but Preskill's responce was "I'll be honest, I didn't understand the talk." A BBC program on the subject suggest Hawking had not really finalised his new concept of black holes so paying $32 will probably leave you none the wiser. "Deciding the matter is a task for a future generation of theoretical physicists." seems to confirm that.
     
  7. Aug 27, 2008 #6

    marcus

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    kev, you are referring to stuff I and others reported and discussed here at PF back in July 2004. The Dublin GR17 conference. Hawking conceding his bet to Preskill etc etc.

    that is not what I meant to focus on in this thread, it is old news.

    what I think has happened in the intervening 4 years is that the "baby universe" alternative has gotten a great deal clearer.

    More people have been writing about it. There are more definite results. If you want you can search by author with names like Pullin, Vandersloot, Steve Hsu... I can't list them all.

    The FQXi just gave a large 2-year grant to a trio of people aiming to look into this alternative (Alexander, Ashtekar, Bojowald). Two of those are big names in quantum gravity and the project description says they plan to involve other people as well.

    So what we are seeing is some research momentum building up, aimed at overturning Hawking's conclusion. It is not that, like Preskill, people just don't understand Hawking's would-be "proof". People attending GR17 in 2004 expressed doubts about it at the time and no one has saluted since then as far as I know (unless you count Lenny Susskind claiming victory :smile:) I don't just mean skepticism about what Hawking presented (and the later paper). what I mean is progress towards an actual solution that goes the other way---information actually going out of our section of the universe into another section.

    This final paragraph of the review by Davies is just a straw in the wind, in effect recognizing what other researchers are doing.
    http://www.nature.com/nature/journal/v454/n7204/full/454579a.html
    Here is the key sentence in the review. I will highlight it:
    allowing information to shift from one region of space-time into another disconnected one, perhaps from our Universe to a newly born 'baby universe'. Susskind dismisses this possibility, but the matter is far from resolved.
     
    Last edited: Aug 27, 2008
  8. Aug 27, 2008 #7

    wolram

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    Last edited: Aug 27, 2008
  9. Aug 27, 2008 #8

    marcus

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    Wolram, I don't know any expert who thinks that BHs have singularities. I mean the BHs that actually exist in nature. Nobody I know of says they have singularities. Maybe one of our PF posters can correct me.

    There is a separate question about General Relativity, the theory (not about Nature). Does GR have singularities? I think most people would agree that it does. But one can challenge this in some specific theoretical case. Say in the case of GR theoretical BHs. The thread you cited is George Jones' thread---you would best ask him what the consensus is about that recent challenge. Someone has claimed that with BHs in GR you don't get theory breakdown. Other people think you do get a BH singularity in GR. It's kind of academic.

    In any case I assume that in nature, with a real black hole, you wouldn't get a singularity.
     
  10. Aug 27, 2008 #9

    wolram

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    I think the singularity is a boil on the bum for GR, the most tested theory, and a major hurdle for QG, if you can get rid of the big one why not the (smaller) ones.
     
  11. Aug 27, 2008 #10

    marcus

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    :rofl:

    well put.

    Indeed QG cosmology models do get rid of the big singularity. That still leaves the problem of finding observations that can test them, but I expect that to come in time.

    So since the big (bang) one is taken care of, one would think that the little (hole) ones would be amenable as well.
     
  12. Aug 30, 2008 #11

    Haelfix

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    The standard problem for the information loss is not the singularity but rather the horizon. The singularity is a point or at least a small epsilon area. The problem is the information density in the rest of the blackhole.

    There is simply too much information spread around the bh and resolving the singularity (into say a remnant) won't suffice to ensure unitarity. It also violates a number of astrophysics bounds b/c an arbitrary number of very massive particles would exist and come into being after a blackhole dies. We'd see a massive amount of decays all over the place, and that is simply not observed. Also the problem itself is defined by avoiding the singularity by looking at slices before the blackhole is formed, and after it has evaporated.

    So the solution, whatever it is, must at the very least resolve both the problem of the horizon (giving it hair) as well as a smoothing of the singularity.
     
  13. Aug 30, 2008 #12

    marcus

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    Hmmm, sounds like you would disagree with Paul Davies, Haelfix. :smile:

    Also your viewpoint would seemingly disagree with Steve Hsu, a particle theorist who often co-authors with Tony Zee. He has also proposed this way of resolving the puzzle. Information leaks out into a large expanding universe. Actually number of people have considered this possibility, Steve Hsu and Paul Davies are just a couple who may be familiar to you. If you would like, I can find you the link to Hsu's paper.
     
    Last edited: Aug 30, 2008
  14. Aug 31, 2008 #13

    Haelfix

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    They know the objection(s) of course, by now the arguments are well documented and have been subject of back and forths for over a decade. But simply removing the spatial singularity doesn't solve the unitarity problem, which is already present long before the singularity occurs. Something really drastic has to occur, and has to occur over a large area such that causality is at least locally ensured.

    So for instance Davies is in the baby universe camp, which is a possible way of bypassing the issue, but most physicists are very skeptical of that sort of line of reasoning and there is no concrete mechanism in place for that to occur, nor is it clear if it even solves the problem (again the dynamics would have to extend much further than the singularity) in generality. You can imagine a very large blackhole where antipodal regions have large crossing times but that have an overdense central region near the singularity. So by hypothesis a baby universe could form somewhere from complicated QG interactions somewhere in that bulk, but its not clear why it would last long enough for it to accurately gauge all the entropy content of whatever mixed states are left over before the hole evaporates such that it keeps unitarity intact on the opposite end. You can actually move the energy scales around a lot in these sorts of exercises, which further makes things tough on them.
    Invariably many of those types of proposals have to wave their hands and posit some complicated global topology changing mechanism.
     
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