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U from Black Hole Bounce

  1. Jul 28, 2004 #1


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    Smolin has presented a testable theory which
    offers a possible explanation for some parameters in the Standard Model
    and in Cosmology.

    In his recent paper he presents a handful of empirical tests which
    could shoot down the theory---that is, the theory is falsifiable: it
    makes predictions which can be tested with available tools and which
    if found not to be the case would invalidate the theory.

    The theory is fairly complicated and depends, among other things, on the idea that our universe is the result of a black hole bounce.
    According to Loop Quantum Gravity and allied approaches (Smolin cites personal communication from Martin Bojowald, but there is also the recent paper of Modesto) when the classical model black hole is quantized the singularity disappears and spacetime extends, forming another universe inaccessible to us from which we can receive no news. In a certain sense the new spacetime ballooning out from the BH "bounce" or quantum ex-singularity is actually in the future from the standpoint of everything in our spacetime (until and if the hole evaporates, upon which causal relation ceases totally).

    If universes are typically created from a black hole bounce, then certain postdictions can be made about the parameters of the Standard Model as well as some observational predictions. The reasoning is rigorous but subtle---best to read Smolin's latest article "Scientific Alternatives to the Anthropic Principle":

    See in particular pages 30-31 "Successes of the theory"
    also section 6.2 answering previous criticisms
    also 6.3 "Why a single heavy pulsar would refute the theory"
    and 6.4 "How observations of the CMB could refute the theory."
    and 6.5 "How early star formation could refute the theory."

    Some sources:

    "The fate of black hole singularities and the parameters of the standard models of particle physics and cosmology"
    http://arxiv.org/gr-qc/9404011 [Broken]

    "Disappearance of the Black Hole Singularity in Quantum Gravity"
    http://arxiv.org/gr-qc/0407097 [Broken]

    "Scientific Alternatives to the Anthropic Principle"
    http://arxiv.org/hep-th/0407213 [Broken]
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Jul 28, 2004 #2
    This seems awful familiar to me. Turok's and Steinhardt's homepage are listed in link as well. I am not forgeting the essence of the thread started Marcus.


    Who thought of these issues, or does everyone get a swing at it from a different perspective?
  4. Jul 29, 2004 #3
    awesome stuff!


    /:set\AI transmedia laboratories

    http://setai-transmedia.com [Broken]
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  5. Jul 29, 2004 #4


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    I agree
    and for me the overall most impressive thing
    is where Smolin says that finding even one pulsar above some mass
    would refute the theory.

    he has a specific model in mind, in other words, that is falsifiable and has some explanatory power.

    If universes really do bud
    thru black holes
    and if the parameters are like genes (constants of nature can change
    slightly as they go thru into the bud)

    then genes that lead to rapid reproduction (lots of black holes) will
    swamp the alternatives

    so evolution would fine-tune certain physical constants---those that govern star formation and gravitational collapse---and he lists some of them and what the effect of varying a bit either way would be on reproductive rate

    so the prediction is that your typical U will be a good black- hole-maker
    and he says some things which if we could find them would show that
    ours is sub-optimal---unlikely according to this theory---which would
    discredit the theory.

    It predicts something that can be looked out for---hence not pure daydreaming.

    so I'm impressed---cant say I want to believe the theory or disbelieve it---but it gets my attention more than any of the other "multiverse" stories.
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  6. Jul 29, 2004 #5


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    the real nuts and bolts multiverse

    It is an idea whose time has come I'd say.
    the key connection is what has been done in Loop Gravity
    getting rid of the BB singularity at the start
    and getting rid of the BH singularity so that a seamless JOINT
    can be made between the two models

    I dont know any other theory of gravity or theory of spacetime
    where you can weld the beginning of a universe onto the bottom of a black hole----maybe you do and if so please give me a link!

    The links here are Modesto 2004 and Bojowald 2001, I'll fetch them later.

    The key logical step is to make it falsifiable. Make it predict something that is already practical to check.
    Smolin has found the only way so far to do this AFAIK----have a testable multiverse. It depends critically on the role of black holes and this
    seamless connection of the two spacetimes. have to go, more later
  7. Jul 29, 2004 #6


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    the usual (non-predictive) multiverse story

    Except for Smolin's the usual multiverse story I've been hearing is not predictive and is invoked to solve some difficulty in string theory or in someone's inflation scenario.

    Like so-and-so's inflation scenario requires a very unlikely and finely-tuned scalar field ('inflaton') and no one can say how that could have happened. So we picture ourselves as a rare fortunate bubble, one of the few bubbles where a quantum hiccup gave just the right inflaton, or we say that somehow a good inflaton got started and has been passed along and we are one of an eternal sequence of inflations----the main thing is the guy is telling you this because his model requires an unlikely bit of luck that he cant give you an ordinary scientific explanation for.

    Or like there are 10100 possible distinct string theories and none has been found that has the right cosmological constant or dark energy density-----traditionally one would want a theory to explain why the CC has to be what it is----but we give up on that, say, and imagine a "landscape" of different string theories and imagine that one of them (that we dont know how to find mathematically) has the right CC----maybe there's a multiverse out there and we live in one of the rare inhabitable bubbles.

    What Smolin is doing is quite different. He is not trying to duck some problem with LQG (not trying to solve a crisis of too many vacuum or an unexplained inflaton)----LQG gives him a multiverse and he starts right away using it to make predictions which can be tested.

    If black holes dont have a singularity in them and the spacetime extends to form a new expanding region with similar (but not identical) fundamental constants then there's an evolutionary situation in which those sets of constants will win out that promote plentiful star formation and lots of collapsing to form black holes. The holiest universes will produce the most babies.

    So the prediction is not that parameters like ours are rare (as in some string multiverse stories----we are one in a jillion because thats the only one allowing "intelligent" life-forms----no no no! Universes with parameters like ours are extremely common! that is what the prediction says. Our physical constants are common because they accelerate the production of black holes

    Sound crazy? OK shoot it down. Find an example, Smolin challenges you, of just one physical constant which, if you made it a few percent different either way, would cause more black holes to form.

    Anyway, that's my take on it---let's hear some others' perspectives. I think Smolin's multiverse story is unique in that it is not a cop-out---not invoked to cover some theoretical embarrassment----and rather than dodging refutation, it courts it: this being the test of meaningful science.
    Last edited: Jul 29, 2004
  8. Jul 30, 2004 #7


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    So many papers have come out eliminating the Big Bang "singularity" that I have lost count
    Bojowald was the first, in 2001, but since then quite a few authors have confirmed the result and extended it to broader assumptions and used different methods to get the result and so on.

    What should the ex-singularity be called?

    In English, more and more frequently people are calling it a "bounce".

    that has the appeal of alliteration (which is favored in English at least in USofA) people can easily switch from "Big Bang" to "Big Bounce"

    Objectively I dont know if bounce is quite right. It is a crossover or transition from contraction to expansion. A reversal.
    A German journalist has called it a "turning inside out"
    which in English would technically be called an "eversion" that is what you do to a sock when you turn it inside out: you evert the sock.

    In fact in the quantum geometry model of the ex-singularity the volume element is turned inside out---I find this puzzling---at the moment of reversal.

    In a popular series of articles about Loop Quantum Cosmology and the new vision of the big bang---quantum bounce in place of classical singularity---Rudy Vaas called it
    "Der Umgesteulpte Urknall"

    knall is bang, Urknall is primordial bang
    stuelpe is something you turn inside out, like a cuff on pantsleg or shirtsleeve
    Umgestuelpte means, so I am told, "turned-inside-out"

    a lot of the progress in Loop Quantum Cosmology is being made in Germany these days, so maybe they have journalistic language rights on
    a piece of the action.
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