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New view of blackhole bounce

  1. Sep 14, 2007 #1


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    In the past two years work by Ashtekar and others in Loop cosmology has modified the LQG dynamics. Two postdocs at Portsmouth, one of whom is an Ashtekar PhD, have recently studied the Schwarzschild blackhole using the improved dynamics. They got some new results which seem to point in the direction of a bounce.

    Loop Quantum Dynamics of the Schwarzschild Interior
    Christian G. Boehmer, Kevin Vandersloot
    15 pages, 13 figures
    (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.

    For some general background here is Andy Hamilton page on Schwarzschild black/white holes

    One of Hamilton's conformal diagrams resembles one of the conformal diagrams in Böhmer Vandersloot's paper.

    Sidenote: if you are a US new QG PhD you pretty much have to go to Canada or Europe to continue career. (string monopolizes postdocs in the US, so no postdoc openings for QG in US). What Kevin did was win a coveted Curie postdoctoral fellowship from the ESF (European Science Foundation) which is normally just for UK and European applicants. He could choose any place in UK or Europe to take the fellowship and he chose Portsmouth.
    Portsmouth is strong in QG and Cosmology and also QC phenomenology (testing by observation). Roy Maartens is there and there is a special institute. So Portsmouth is a good place to go and it's not surprising that two postdocs like Böhmer and Vandersloot go there and meet up.

    I'm still trying to figure out what Kevin and Christian's new paper concludes about what happens in a black hole. The results, which are suggestive rather than conclusive, overrides the "singularity" which occurs in classical GR. They find two possibilities, both needing further exploration.

    Hi Kurt, thanks for the NewSci link--their article is a general introduction to the "baby universe" topic--and has pictures.
    You commented:
    That is certainly right and a BOOK has even been written about it called The Life of the Cosmos, plus also many scholarly papers.

    What is new about Kevin and Christian's work is they do new analysis, use a new QG dynamics, and run a lot of numerical work on the computer. They do not START with the idea that there is a bounce-baby, they start with a leading candidate model---the best currently available to replace GR at singularities IMO---and they SEE if there is a bounce. In fact in one case they do not get it, and in the other case they get the bounce. So they are trying out different versions of a LQG model blackhole to see what actually happens (with that model).

    The idea of a bounce-baby is not new (I think John Wheeler proposed it several decades ago) but now we are seeing more progress studying the details.
    Last edited: Sep 14, 2007
  2. jcsd
  3. Sep 14, 2007 #2
    This is an interesting theory, so, correct me im wrong, they believe, out of the mathematics, that the singularity is another universe. If this is correct, it would be interesting to see if this universe is still connected (like the first stages of a baby universe [see for more info (pic)


    Or if this Universe is like the last stages of a baby universe. One thing that is curious, if something falls into this black hole, what will happen, will the thing go into this new universe?

    This theory of a specific type of universe being connected to a black hole isnt relatively new theory (by relative, im referring to within the last 10 years).
  4. Sep 15, 2007 #3
    Hello Marcus,
    I got a bit lost when you mentioned bounce and bounce-baby. What exactly are you referring to?
  5. Sep 15, 2007 #4


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    sorry, I was speaking too informally and even a bit flippantly.
    the BH BOUNCE is the topic of the thread.
    The authors mention the bounce idea on page 7 of the paper we're looking at:

    it means the resolution of the singularity by replacing GR with a quantized version of GR which does not break down there-----where instead of a breakdown you get re-expansion

    So you get a new expanding region of spacetime often called a "baby universe"

    this is a pretty common idea these days and I think your earlier posts indicate you know about that idea. And you also pointed out the fact that the idea is NOT NEW. In fact it is old and I think goes back to J.A.Wheeler which would put it perhaps as early as 1970.
    Smolin was writing papers about the idea as early as 1993 and I seem to recall he cited Wheeler from much earlier.

    My unserious expression "bounce-baby" just puts the two terms together to refer to a BH bounce resulting in a baby universe. I don't mean to suggest that the baby universe has to be smaller or less massive just because it is a "baby". Babies could presumably grow. Although inflation in general is still something of a mystery.

    I am trying to think what might puzzle you about the term BOUNCE and perhaps you have not encountered it much in your reading yet. There is a large QG literature about it but it mostly is about the cosmological singularity. The QG models studied so far by Ashtekar, Bojowald, and their co-workers tend to replace the bigbang singularity with a bounce. Our region of spacetime, our universe, results from a prior collapsing region---during collapse the density reaches a critical level at which quantum corrections dominate and make the effect of gravity be repellent---collapse bounces and turns into re-expansion.

    There are many papers about this by many people, but since this thread is about a Vandersloot (and his co-author Boehmer) I will just cite a recent Vandersloot paper about the cosmological bounce. This will have references to other bounce-related papers and will serve as one example of many:

    The behavior of non-linear anisotropies in bouncing Bianchi I models of loop quantum cosmology
    Dah-Wei Chiou, Kevin Vandersloot
    15 pages, 10 figures
    (Submitted on 17 Jul 2007)

    "In homogeneous and isotropic loop quantum cosmology, gravity can behave repulsively at Planckian energy densities leading to the replacement of the big bang singularity with a big bounce. Yet in any bouncing scenario it is important to include non-linear effects from anisotropies which typically grow during the collapsing phase. We investigate the dynamics of a Bianchi I anisotropic model within the framework of loop quantum cosmology. Using effective semi-classical equations of motion to study the dynamics, we show that the big bounce is still predicted with only differences in detail arising from the inclusion of anisotropies. We show that the anisotropic shear term grows during the collapsing phase, but remains finite through the bounce. Immediately following the bounce, the anisotropies decay and with the inclusion of matter with equation of state w < +1, the universe isotropizes in the expanding phase."

    UPDATE TO REPLY to next post:
    Hi Kurt, as you know there's two kinds of writing on topics like this (1) books written for general audience and (2) research papers and books written for specialists.

    (1) the best general audience book I know of from a QG perspective about how the universe could result from a bounce is the one by Smolin called
    The Life of the Cosmos

    this is quite non-technical if I remember right. It was published in 1999 and the field has developed a lot since then so that there is a lot more mathematically detailed modeling of the bounce.

    however even without a detailed model he manages to make TESTABLE PREDICTIONS in this book based on assuming how the universe evolved. the predictions are subject to test by astronomical observation (e.g. measuring the masses of neutron stars) and have not yet been shown false.

    but there OUGHT to be some more recent general audience books about this and there aren't as far as I know, so we are down to

    (2) technical articles. For that, look in the references of that Vandersloot paper. There are plenty of articles reporting recent research by e.g. Bojowald and the group headed by Ashtekar.
    You might also look in this thread
    This gives a link to recent articles in the monthly journal Nature Physics that discuss the bounce, and also they are written for other scientists who are nonspecialists---so the style is not too technical.
    there's plenty more. but try those for starters
    Last edited: Sep 15, 2007
  6. Sep 15, 2007 #5
    Thank-you marcus,
    What puzzled me about the term bounce was that I have herd the term in a theory of the creation of the universe where our universe expands then contracts right back to the singularity the "bounces" back and re expands, in fact im pretty sure that its called a cyclic universe, here is an interesting paper on it [http://space.newscientist.com/article/dn9114] [Broken]

    if the link does not work, just in new scientist search the following:
    'Cyclic universe' can explain cosmological constant

    ah, i remember, its uses the word bounce in the first sentence. Now the term seams to make sense. Thanks

    You mentioned that there is alot of literature on QG which deals with the cosmological singularity, sounds interesting, whats the best book on this subject that you would recommend?

    You mentioned something along the lines of: Babies could presumably grow; but we dont really understand inflation.

    It would be interesting to know if our laws of physics i.e. the four fundamental forces would kinda leak or not so much leak but continue on with this baby universe or this baby universe would get an entire new set of laws. In this case anything could happen, one being that inflation would not work, presumably if inflation is due to the breakaway of gravity from the Super force, or, a more recent theory, no inflatons would exist, and then it would not expand as fast and, according to the theory, there would then be no dark matter, in which case the mass of the universe would be small, and that could lead to the universe collapsing on its self, but wait, it might not due to some "new" fundamental force that was issued to this universe.

    Whats your line of thought on that marcus? If you have not herd of the inflaton, which is a theorized particle, then here is the new scientist link on the subject

    Its a pretty interesting and new theory, what do ya think?
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