Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Quantum nature of big bang (new Ashtekar paper)

  1. Feb 22, 2006 #1


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    this just out


    final sentence of conclusions:
    "...our results show that the quantum geometry in the Planck regime serves as a ‘quantum bridge’ between large classical universes, one contracting and the other expanding."

    words leading up to the above:
    "...we constructed the physical Hilbert space, Dirac observables and semiclassical states, thereby extracting physics of the Planck regime, going significantly beyond the demonstration of singularity resolution..."


    here's the usual abstract information:
    Quantum Nature of the Big Bang
    Abhay Ashtekar, Tomasz Pawlowski, Parampreet Singh
    4 Pages, 2 Figures

    "Some long standing issues concerning the quantum nature of the big bang are resolved in the context of homogeneous isotropic models with a scalar field. Specifically, the known results on the resolution of the big bang singularity in loop quantum gravity are significantly extended as follows: i) the scalar field is shown to serve as an internal clock, thereby providing a detailed realization of the 'emergent time' idea; ii) the physical Hilbert space, Dirac observables and semi-classical states are constructed rigorously; iii) the Hamiltonian constraint is solved numerically to show that the big bang is replaced by a big bounce. Thanks to the non-perturbative, background independent methods, unlike in other approaches the quantum evolution is deterministic across the deep Planck regime."

    So Ashtekar has officially signed on deterministic bounce, connecting contracting regions to expanding ones.
    Where I think this is leading is that he---or someone continuing his line of investigation---may eventually take issue with Stephen Hawking's claimed resolution of black hole information "loss". If there is a bounce in the hole then information that appears "lost" comes out on the other side of the Planck regime to an expanding continuation of spacetime. No loss, it's just a fork in the road of time.
    Last edited: Feb 22, 2006
  2. jcsd
  3. Feb 23, 2006 #2


    User Avatar
    Science Advisor

    How did you reach to the conclusion that this has something to do with black holes? I did not understand the paper however I found no mention there about black holes, but about big-crunch.
  4. Feb 23, 2006 #3


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I presented that as my own hunch---just a guess as to where it's going

    there is nothing in the paper about black holes (as you point out).

    I have not reached any CONCLUSION (that's your word) but rather am guessing about a possible future development, to put this paper into context.


    The hunch, or inkling of possibility, that there could be connection between black hole and big bang events does not, of course, originate with me. It goes back in the scientific literature ten years or more----at least to Smolin's papers of 1994 and 1995 and probably earlier!
    The Fate of Black Hole Singularities...
    And Smolin (1994) cites John Archibald Wheeler.

    What we have seen in recent years is an increase in research activity (in loop gravity and cosmology) around the removal of bang and hole singularities---which are replaced in the loop model by a bounce.

    In 2004 and 2005 black hole bounce was written about by half a dozen people IIRC and the similarity to the "big" bounce replacing the cosmological singularity was pointed out.

    Ashtekar has been dropping hints about the possible connection between the two kinds of bounce, he is comparatively cautious. Since the connection between black hole bounce and cosmological ("big bang") bounce is, at this point, merely SPECULATIVE, based on a similarity of mathematical treatment, none of the new people will be too explicit.

    If you want to check out articles related to black hole bounce, do an arxiv search for authors like

    Leonardo Modesto
    Viqar Husain
    Oliver Winkler
    Martin Bojowald
    Parampreet Singh

    Most of the relevant papers appeared on arxiv in the past year (2005), some in 2004.

    Papers on the cosmological "big bang" bounce go back mostly to 2001, the field of loop quantum cosmology really got started with Bojowald's paper of that year, removing the cosmological singularity.


    hellfire, I would say that the important thing is not to attribute too much certainty to these things at this point. So far I see people mainly just pointing out MATHEMATICAL SIMILARITY between the two bounce regimes----they use similar mathematical models. And remember that the models themselves have to be TESTED, so there is quite a lot to do before this can be discussed with any degree of confidence.

    The people studying black hole bounce borrow their tools from the papers about cosmological bounce.

    Some occasionaly voice the suspicion that they may be dealing with the same thing------but there is still a lot of work to be done on black hole bounce.

    These things have been investigated with simplifying assumptions of symmetry. currently the job is to extend the analysis to more general cases, relaxing the assumptions.

    Would you like help finding arxiv numbers for some of the reasearch on cosmological and black hole bounce? You are an old hand at this and I suspect you may either already know some of the literature on this, or else can look it up on your own.
    Last edited: Feb 23, 2006
  5. Feb 23, 2006 #4


    User Avatar
    Science Advisor

    Please, don't take my comment as a criticism to you. People like me who are not very up to date in quantum gravity and quantum cosmology have sometimes difficulty to distinguish what is a well-founded conclusion and what is a speculative idea. Im my eyes, that paper by Smolin (actually that one I did already knew) is a wild guess compared to that by Ashtekar.
  6. Feb 23, 2006 #5


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    You are right! (IMO)

    there is a big difference between the 1994 Smolin and the 2006 Ashtekar.

    I should get you more links from the 2005 crop of papers, some of which dealt with removing the BH singularity.

    I have to run out on some errands now, but will get back to this.

    As I see it, the singularity removal, and the bounce business, is still somewhat speculative or at least inconclusive. But what impresses me is the gradual progress.

    Over the past 10 years the whole thing has been gradually firming up. More and more details of the mathematical models have been filled in. More people have started working on it.

    Besides the papers on arxiv, there are some online recorded seminar talks at Penn State from the Fall 2005 semester, by Parampreet Singh and others. One I think by Ashtekar.

    I want very much to help you find some recent papers because I think your critical reading will supplement mine and help evaluate this.

    I have become persuaded that this BH and BB bounce business is firming up to the point NOT that you can say it is RIGHT but that one can expect some kind of test. I don't know what the test will be, but the models are getting explicit enough that I think some way will be found.
    And then the loop picture of BH and BB could turn out to be falsified, or it might survive testing. But either way it is solidifying enough that I expect testable predictions from some aspect of it to come out.

    back later
  7. Feb 24, 2006 #6


    User Avatar
    Science Advisor
    Gold Member

    I agree with marcus on the implications regarding black holes. There is no information loss if an inverted universe results from the 'bounce' [WRT our reference frame]. This is a very interesting paper [Ashtekar, go figure]. I anticipate it will be heavily cited. My question: is there a causality break between the newly created universe and its 'mother'? I think there should be, but I admit that is pure speculation. Should the 'mother' black hole 'die' by evaporation or merger, I am concerned about the apparent paradox this would create for its offspring.
  8. Feb 24, 2006 #7


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I also think there should be (but am not certain) because if the conjecture is right (still a longshot but serious enough to be discussed and checked) then the black hole that gave rise to our spacetime region is entirely in our past.

    whatever happeneth to that "parent" BH can no longer affect us in the least, or so I suppose

    I emphasize that I can't answer confidently---this is just what I think. I imagine two BHs in our observable universe, where each collapse has given rise to a separate expanding continuation of spacetime and I imagine the situation which you suggested: they subsequently merge. I imagine that this merger cannot any more affect the two offshoot histories.

    because the merger happens in our spacetime region where we can see it, but for "them" in the extensions everything involving the BH is way in their past-----

    Times marches on (as GWB might say) and they get off scotfree.

    At least I hope so, Chronos:smile:

    it would terribly terribly awkward if a BH merger would retroactively merge the resulting spacetime histories----arrrrgh!:yuck:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook