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Black hole universe

  1. Mar 22, 2005 #1
    I know little about this but supposedly there is some thinking coming from LQG that black holes might be new universes and that our own universe may itself be a black hole birthed from another.

    Black holes are constantly both gaining and losing energy. Assuming our universe is a black hole (which of course is assuming quite a lot) I wonder if this gain and loss of energy could somehow be observed from our perspective, maybe as something like the effects of dark energy say. Has this been at all discussed or is there some obvious answer? Any information, ideas, or comments?
  2. jcsd
  3. Mar 22, 2005 #2


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    if you havent already done so, take a look at Smolin's article
    http://arxiv.org/hep-th/0407213 [Broken]
    Scientific alternatives to the anthropic principle

    which Cambridge U. Press is publishing as part of a collection

    the important thing with a theory like that is that it be falsifiable in other words it has to predict something definite about a future experiment or observation so that it can be refuted if it turns out wrong

    otherwise it is empty, it has no predictive power if it is so mushy that it can accomodate any future outcome of any future experiment.

    the point about Smolin CNS (cosmic natural selection) model is that it is predictive so that it bets its life on its predictions and could be shot down next month or next year if something is found that contradicts.

    it is, however, an extremely farfetched and strange theory, so dont get your hopes up!

    it is based on the fact that LQG has succeeded in or is in process of removing the classical BB and BH singularities by quantum regimes of bounded (although uncertain) curvature and density which LOOK MATHEMATICALLY SIMILAR at least on some superficial level.

    more on this just came out last week with the paper by Bojowald et al
    http://arxiv.org/gr-qc/0503041 [Broken]

    the key thing is that while classical 1915 Gen Rel. fails to compute and generates infinities and generally breaks down and goes haywire at the classical "singularities" by contrast LQG does not break down and keeps on computing THRU where the other theory throws a fit.

    so mathematically one can see a bridge forming between the BH collapse and the onset of BB expansion.

    also in the LQG model inflation (with a graceful exit) turns out to be generic. it does not require a lot of extra paraphernalia or fine tuning, it just appears in the natural evolution at the proper time and then goes away after a brief spell of very rapid expansion.

    because inflation can create matter, in apparent violation of conservation laws, you dont have to worry about the offspring universes that bud off of our universe at its black holes growing up to be RUNTS
    even though only a few stellar masses of our matter goes into the hole
    a full universe worth of matter can come out in the resulting bigbang, because of inflation (which Alan Guth sometimes calles a "free lunch")

    the analysis getting rid of the BH singularity hasnt been completed, see the Bojowald et al paper about this
    and there are a lot of loose ends and things to clear up

    and even when (if) a consistent theory of this kind of universe is successfully constructed, which is what we see happening, it still has to be tested by experiment or observation AND IT STILL COULD BE WRONG

    but it does seem to be interesting, and one can watch the pieces gradually fall into place
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  4. Mar 22, 2005 #3


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    a black hole is a oneway street
    the timelike directions all point down the hole
    so whatever universe might expand down there cannot affect in any way what happens here, or send us any signals.
    Causally speaking, what is down there is entirely in the future of everything in our universe

    what happens to the budded off, branched off, forked off universe when the black hole in our universe evaporates?
    I dont know and i didnt see anyone tackle that question. the theory is not complete. the pieces are still being put together
  5. Mar 22, 2005 #4
    Chroot (Warren) will surely throw me out of PF now, but this post is so directly related to original post of this thread that I must give the essence of Appendix 3 of Dark Visitor (www.DarkVisitor.com for more). Please note that this is just interesting "playing around" not the strictly valid physics in rest of book. (A physic text, disguised as a scary story, trying to attract bright "pre-law students" etc. to physics, despite the lower salaries, etc.)

    I surely would be allowed to cite this reference, if I were not the author of it. Note you can read entire book for free -instructions at the webpage - so this is not an effort to profit, but as explained there, to help strengthen science in the western world, save good jobs, etc..

    Let a proton, some distance from Black Hole fall half the remaining distance towards the BH. (step 1)
    The work done on it in step 1 is greater than force of gravity acting on it at beginning of the step time times the distance of travel (Call it W1) This is a "floor estimate" for energy gain by the proton in step 1.
    In step 2 it also falls half the remaining distance, (half of step 1 distance) but the force acting on it at the start of step two, used in the "energy floor estimate" is 4 times larger, so in step 2 the energy gain W2 is at least twice W1, but assume it was only W1 again.
    Repeat same analysis for step 3 and step n - every step gives at least W1 to the infalling proton, but it never gets to point singularity of the BH in any finite number of these "half the remaining distance steps."

    W1+W1+W1+ ..... is a divergent sum. That is, each particle that joins the singularity gains infinite energy - "Infinite energy" in "zero volume" is very much like the big bang that started our universe. Just a speculation, but interesting to think that each black hole could be some other universe's Big Bang. Physic is more complex that this simple model, but you get the idea.

    Book deals with some complex physics, (See list at web site.) but threre as here, it keeps it simple enough (no calculus etc.) for highschool student, especially because the ones not interested in science, but smart, are my target reader and I hope to scare them with my possible cosmic disaster story enough to become interested to know if it is possible that the ice age might return soon.
  6. Mar 22, 2005 #5


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    I have the same problem with BH evaporation. What is unknown, and probably unknowable, is if any causal connection remains between this universe and what lies inside the event horizon once a BH forms. What ultimately evaporates in this universe may be no more than an empty egg shell.
  7. Mar 22, 2005 #6


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    sounds like an idea. i'll think about it.
  8. Mar 23, 2005 #7
    Thanks for the information Marcus I'll definitely take a look at those links. My main question, put a little differently, is as the black hole in our universe grows or shrinks what happens from the perspective of the black hole universe? You pretty much address this I think with your very interesting scenario of a black hole completely evaporating. So the theory at this point doesn't seem to know whether there is any connection at all between universes yet. One scenario I suppose has at the moment the black hole forms the entire universe, from birth to death, fully described like a photograph taken in an instant. Another scenario could have only initial conditions and a bang being decided at the black holes initial formation allowing for signals from the host universe to influence its evolution. Maybe there is even a possibility that at every moment, in our universe, of a black holes life a new universe is born of that black hole in the snap shot fashion based on its current condition.. or (perhaps more likely) is there something special that happens at the very moment of a black hole coming into existence that is not happening from one moment to the next in a black holes life? Anyways, this is pretty much where I'm at :tongue:
    Last edited: Mar 23, 2005
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