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Black hole bounce comes out of the closet

  1. Sep 20, 2005 #1


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    This is a long-awaited paper.

    Quantum geometry and the Schwarzschild singularity
    Abhay Ashtekar, Martin Bojowald
    31 pages, 1 figure
    IGPG-05-09/01, AEI-2005-132
    "In homogeneous cosmologies, quantum geometry effects lead to a resolution of the classical singularity without having to invoke special boundary conditions at the singularity or introduce ad-hoc elements such as unphysical matter. The same effects are shown to lead to a resolution of the Schwarzschild singularity. The resulting quantum extension of space-time is likely to have significant implications to the black hole evaporation process. Similarities and differences with the situation in quantum geometrodynamics are pointed out."


    "Results of the last two sections support a general scenario that has emerged from the analysis of singularities in quantum cosmology. It suggests that the classical singularity does not represent a final frontier; the physical space-time does not end there. In the Planck regime, quantum fluctuations do indeed become so strong that the classical description breaks down. The space-time continuum of classical general relativity is replaced by discrete quantum geometry which remains regular during the transition through what was a classical singularity. Certain similarities between the Kantowski-Sachs model analyzed here and a cosmological model which has been studied in detail [10] suggest that there would be a quantum bounce to another large classical region. If this is borne out by detailed numerical calculations, one would conclude that quantum geometry in the Planck regime serves as a bridge between two large classical regions. Space-time may be much larger than general relativity has had us believe."

    In the past, Ashtekar has been cautious about broaching this possibility. IIRC about a year ago he gave a seminar talk about LQG quantum black hole and his work with Bojowald. The two later published a paper on BH evaporation ( http://www.arxiv.org/abs/gr-qc/0504029 ) which was worded in a very reserved way.

    In this paper he comes closer to saying that spacetime might re-expand from the pit of a black hole, forming another tract of the universe by another bang. In my view, he still does not say this unreservedly. There is another paper in the works, reference [10], with Parampreet Singh.
    Last edited: Sep 20, 2005
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  3. Sep 20, 2005 #2


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    Yes, the seminar Ashtekar gave was exactly a year ago
    20 September 2004
    at Penn State, on topic of BH evaporation
    http://www.phys.psu.edu/events/index.html [Broken]
    select Fall 2004 from the menu and scroll down to 20 September.

    You can download the Audio and Slides for this talk

    This talk seemed to me to evade the issue of black hole bounce.

    then there was the Asht. Bojo. paper on BH evaporation
    and that, in my estimation, just vaguely hinted at it, obliquely.

    then Bojowald came out with something on his own that confronted the possibility a little more definitely
    Nonsingular Black Holes and Degrees of Freedom in Quantum Gravity
    Martin Bojowald
    4 pages
    Phys.Rev.Lett. 95 (2005) 061301
    "Spherically symmetric space-times provide many examples for interesting black hole solutions, which classically are all singular. Following a general program, space-like singularities in spherically symmetric quantum geometry, as well as other inhomogeneous models, are shown to be absent...."

    "Key features are that densitized triads as basic variables in quantum geometry provide us with a local internal time taking values at two sides of the classical singularity, combined with a quantum evolution that connects both sides. No new ingredients are necessary for inhomogeneous singularities, only an application of the general scheme to the new and more complicated situation.... Since the difference equation for psi has the same form as that in homogeneous loop quantum cosmology, the number of quantum degrees of freedom is formally related to the initial value problem of quantum cosmology. A possible physical meaning is to be checked in explicit examples... "

    In this solo paper Bojowald says the degrees of freedom match up between a BH collapse and a BB expansion, in the simplified models he is discussing, and that a possible meaning is to be checked. But he doesnt come right out and say maybe the pit of a BH continues into a BB.

    Now we have this Asht./Bojo collaborative paper which explicitly says "black hole bounce" opening up another huge region of spacetime

    and Ashtekar further says he has a paper ("reference [10]") with details in preparation with Parampreet Singh. so things are moving along at a nice deliberate pace.
    Last edited by a moderator: May 2, 2017
  4. Sep 20, 2005 #3


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    Marcus, the recurring issue I see here is there is no way a singularity, once formed, can ever be made to mathematically go away. They appear to be eternal [at least within their own reference frame.] A pretty powerful, if obscure argument favoring the CNS conjecture in my mind.
  5. Sep 20, 2005 #4
    I actually removed the "perceptional-bounce" from this thread some years ago:https://www.physicsforums.com/showthread.php?p=160158#post160158

    see Vast's reply #39 ?

    But as you know I have been banding this around for a number of years, Iam actually on my 'fourth- road' as far as handles go!

    I have expected this for some time, its the "natural" progression for the theory I have:Theory Of Entropic States.

    Which I am NOT going to discuss!

    Just a point of historical fact, I have a number of really interesting threads from these very forums, that go back a long time,and all my posts have been copied, one reason I have removed some parts of my really interesting threads, is that I have had to wait for academics such as Bojowald to cotton on to the 'obvious' problems of Universal Singularity, and the Galactic Singularity, being not "one-and-the-same".

    Back to the paper, I am as you know a really..really great admirer of Parampreet Singh, the fact that I have highlighted many of his papers here as on other forums, gives me great pleasure, as It must you.

    I will hopefully finish some things I have to do, and read the papers you have highlighted, thanks again for keeping up to the minute for linking relevant papers marcus.
  6. Sep 20, 2005 #5
  7. Sep 20, 2005 #6


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    Easy does it. go easy on yourself
    most of OUR job is just to wait, albeit alertly and mindfully

    BTW the "in preparation" paper is

    "[10] Ashtekar A, Pawlowski T and Singh P 2005 Quantum nature of the big bang: An analytical and numerical study Preprint in preparation"

    what I think is happening is this: Bojo original study of BB (removing singularity and extending back) was done with a simplified model

    homog and isotropic-----so a very uniform model with only a few degrees of freedom, suggestive of what the full theory would do, but not the full theory.

    working in the full theory is computationally difficult----people normally have to resort to numerical (computer) methods---running case after case and plotting results

    the same is true for the BH, to do a really satisfactory job one cannot make these simplifying assumptions-----after all BH spacetime is not homogenous! and matter should be included, and so on.


    we watchers expect that if they do a good job of modeling the Bang (drilling into mountain from the East side)
    and if they do a good job of modeling the Hole (drilling into mountain from the West side)

    that their two tunnels will meet inside the mountain and join up.

    so then the two Bugaboos of anti-science reaction will have merged and bigbang cosmology will become a variety of Ev:surprisedluti:surprisedn

    creationist Throw-backs will be pissed, they will have to regroup and make another papier-maché parade-float divine principle
    and naturalists like me can sing songs and dance around the circle

    But there is no urgency. It will take Astekar and his Postdocs many a moon to drill these two tunnels into the mountain.
    Last edited: Sep 20, 2005
  8. Sep 22, 2005 #7
    So is a black hole a one,two,three, or four dimensional object beyond the event horizon ???
  9. Sep 22, 2005 #8


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    the Schwarzschild spacetime is a 4D spacetime
    I find it real hard to visualize how the lightcones go towards the singularity.
    would be great if someone else could provide some intuition

    somehow it is a 4D spacetime in which the singularity is in everybody's future (everybody who is inside)

    somehow you cant SEE where you are going either, you can't see your future (Haelfix or somebody correct me if I am wrong) because light from what is up ahead cannot get to you
  10. Sep 23, 2005 #9
    so it is spherical then ???

    as in, if viewed from another place on the opposite side of where we see it from, it would still register as a hole and look exactly the same ???

    I'd always thought of it as a 2d veil or maybe just a 1d temporal object
  11. Sep 24, 2005 #10


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    you need a website where there are pictures
    (I too, I would like a website like Andy Hamilton's Uni Colorado one PLUS some "penrose-diagrams" that one sees in the slides for seminar talks at Penn State archive of seminar talks. I would like to beef up my intuition. BHs are not easy to understand, I think)

    but you need pictures even more, I think.
    Maybe I can get some links, but the best would be if Haelfix volunteered---he is a graduate student in astrophysics at Penn State and comes here sometimes.

    If he does not volunteer, then I advise you to start a thread in Astronomy forum that says simply
    "Help. I need spacetime diagrams for black holes."

    then probably SpaceTiger will come and give you links. or Hurkyl, being a mathematician he may know where helpful BH diagrams are

    Dmbgga, you must know what is a "spacetime diagram"
    This is a TWO DIMENSIONAL simplification that you can draw on a piece of paper. TIME is in the up down direction (up is to the future)
    and space is collapsed to just one horizontal right-left direction

    the 45 degree line is how light goes----this is a convention everyone uses---so the forward and backward lightcones are simply triangles with 45 degree sides

    If it is a diagram of a black hole then the space direction corresponds to RADIAL DISTANCE and the diagram is very unrealistic and distorted but it is just a schematic that helps people discuss things and in this case it is called a PENROSE DIAGRAM or sometimes called by some other name that I forget.

    And the singularity is drawn as a horizontal jagged zigzag line, like the PAPER WAS TORN there

    and from every point inside the event horizon the two 45 degree lines that go out (describing the lightcone or the future from that point) both go to that jagged tear, to that 'rip' in the picture-----this shows that all the lightcones go to the singularity

    one can imagine that in a more realistic picture the lightcones are curved and their sides come together and they all FUNNEL to the singularity and one can imagine more picturesque things, but this penrose diagram is like a CONFORMAL picture in which the lightcones have straight sides. It has been stretched out and deformed to make a simpler picture---and the price paid for this is that the singularity has been stretched out to be a horizontal line segment. NO PICTURE COMPLETELY MAKES SENSE and no one image will serve all purposes.

    but I advise you to find a website with these penrose diagrams and study them a little.
    Last edited: Sep 24, 2005
  12. Sep 24, 2005 #11
    congratulations Marcus...

    ...dumbugga is correct :biggrin:

    but is not the rip you speak of in the 2d paper diagram supposedly resolved in this new Ashtekar/Bojowald paper such that the singularity is removed thus making the diagram inconsequential as the lightcone doesn't collapse to the singularity in a blackhole ???

    re: my last post i just asked 2 simple questions requiring a yes/no answer.

    I understand the analogy to a funnel type descent of light to a singularity as in water swirling vortex like towards a point in a whirlpool...

    ...so does that men if you got behind a black hole you would see a funnel like appearance of blackness and imply that we can then only see black holes perpendicular to our point of view ???

    Am I right to assume in this paper that a black hole is a one dimensional planck size point in spacetime which sucks energy in the form of light out of our universe like a bubble deflating and blowing it out into another by a white hole ???

    Going back to the whirlpool analogy...

    Instead of water descending funnel like towards a point beneath the surface, it would be as if the centre of the vortex were on the surface of the water. The build up waiting to get sucked through a pinpoint causes a black appearance in spacetime when applied to light no matter where you view it from meaning a blackhole must be spherical in appearance from all sides. Must it not ???

    Imagine spherical pools of water rippling and getting sucked towards towards the centre but only taking the hydrogen atoms first.
  13. Sep 24, 2005 #12


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    it collapses to something so small that we would think of it as a point

    but it is not a SINGULARITY

    in mathematics a "singularity" is a place where the theory breaks down

    when I say that in LQG the star does not collapse to a singularity, what i mean is only that the theory does not break down-----it still goes to something very like a point

    maybe it has millimeter radius (ONLY NOT ZERO)

    maybe it has planck density, similar to what people talk about density at big bang time (ONLY NOT INFINITY DENSITY)

    maybe it is 1090 times denser than water, but not infinitely denser
    maybe it is 1025 times hotter than the core of the sun, but not infinitely hotter

    so we can still do physics, and we find that it continues out the "bottom" into a big bang-type expansion


    it is conditions at that edge that it is very hot, and very dense, and where quantum gravity----quantum spacetime dynamics----takes over, and it is what Ashtekar calls the "quantum regime" that the material of the star must pass through and prepare conditions for another energy-creating and spacetime-creating inflation

    If I remember correctly the figures for temperature and density (which I recall only approximately) were estimated in a paper by Ganeshyam Date and Golam Mortuza Hossain called

    Genericness of Big Bounce in isotropic loop quantum cosmology

    or else the one by the same authors called
    Genericness of inflation in isotropic loop quantum cosmology

    But what they said is what other writers say too: that at a LQG bounce the temp goes up to around planck temp and the density goes up to around planck density. (that is why I say 1025 times the suncore temp and 1090 times standard density) the pressure is also reckoned to be very high but not infinite)

    This stuff is very preliminary and there is plenty of chance of it being wrong. But anyway that is what to think of replacing the torn edge of the piece of paper with.
    Last edited: Sep 24, 2005
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