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Big Bang Question

  1. Feb 17, 2008 #1
    By definition, the gravitational force associated with a black hole precludes anything, even energy, from escaping once inside the event horizon, hence the name. If all of the matter and energy which exist in the Universe today were supposedly once contained within a space no bigger than a proton wouldn't that equate to a single enormous black hole? How did the Universe escape from it?
     
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  3. Feb 17, 2008 #2
    I think that has something to do with the theory that once matter is at a certain density (80% Plank) it has the ability to repel, which would then allow the universe to expand. I'm not sure though, and I'm very new to this stuff so I'd wait for someone else to reply, but there's my 2 cents. I'm not sure if those definitions and statements are exactly right that you said, but I'll wait for someone else to say so.
     
  4. Feb 17, 2008 #3

    marcus

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    No, because the universe was expanding.

    I don't accept that modern cosmology says "all matter and energy which exist in the Universe today were supposedly once contained within a space no bigger than a proton ".

    Expansion may have started with a considerably larger, or even an infinite, volume. What you say sounds like a popularization or a misconception to me. But this doesnt matter. Density was in any case extremely high at start of expansion, according to pretty much any model.


    A very high density region that is not expanding will collapse, and the formula for the Schwarzschild radius which you may know about does apply in that case.

    But if the region is expanding it is a whole other ball game.

    So there is no problem about the Universe "escaping" from its initial high density state.

    Expansion was roaring along at an almost inconceivable rate at that point.
    =============================

    what I am telling you is just what you get when you take a model based on our best law of gravity (Gen Rel) and fitting the observational data, and run it back in time.

    The classical model only goes back to right after expansion began and doesnt explain how it started. Some recent quantum models go back to before expansion began and explain how it could have gotten started.

    We don't know yet what the right model is of the very early universe and the start of expansion. Some do a pretty good job of explaining but they need to be tested. I'm in a kind of wait and see mode, myself.

    But certainly what you are worried about is a non-problem. Any model we use says the Hubble parameter was huge enough at early times to completely overwhelm any tendency to make a black hole :smile:
     
  5. Apr 11, 2008 #4
    Thermodynamics, gravity, etc

    The definition is correct BUT the situation for the Big Bang is different than the normal formation of a black hole. Consider the possibility that the universe could collapse. The black hole created in this collapse do not collapse to an infinitely small diameter. The second law of thermodynamics requires that as more matter is added to a black hole it gets BIGGER not smaller. Thus the situation at the Big Bang cannot be obtained.

    However, the Big Bang expansion implies that the initial entropy was larger than that required for a black hole of the same diamter. Thus expansion would take place to reach this thermodynamic equilibrium. Also at Big Bang starting dimensions Einstein's theory of gravity has a replusive part related to the energy. This would force an expansion. Third, inflation theory would cause expansion due to the negative pressure involved.

    The question is: Are these effects enough to drive the expanding universe past the corresponding black hole diameter. As far as I know, this is not known.
     
  6. Apr 11, 2008 #5

    marcus

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    I don't understand what you are asking, Golfer.
    What do you think "the corresponding black hole diameter" is?

    What universe distance do you think should be compared to that? Do you have an estimate of the diameter of the universe?
     
  7. Apr 11, 2008 #6
    That is a great question, it got me to ponder!
    From what I understand that is the problem with the Big Bang Theory, its called the Singularity. Our universe laws did not exist; therefore we cannot explain why it happened.

    Although I seam to remember reading about M theory having to do with the Singularity but I don’t remember much of the details.
     
  8. Apr 11, 2008 #7

    marcus

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    Just to be clear I'll repeat. No.
    It would not "equate to a single enormous black hole".

    There are a bunch of different solutions to the equation of GR which involve very high density. The black hole solution is just one, and it can't accomodate rapid expansion.

    You can think of it intuitively like this (Wallace correct me if I'm wrong here) expansion at the rate that must have prevailed initially would *tear apart* any black hole that tried to form, before it could even start collapsing.

    According to standard expansion cosmology (the Big Bang, in pop-talk) it doesnt make sense to equate the initial conditions at the start of expansion with a black hole.
    (However in quantum cosmology, the possibility does tentatively arise that the expansion of our spacetime was preceded by gravitational collapse in a prior region---quantum gravity allows for gravity to reverse at very high density and cause a "bounce". I am not talking about quantum cosmology here, just the standard picture.)
     
  9. Apr 11, 2008 #8
    One cannot simply stitch Schwarzschild-deSitter solutions for high density regions inside a FRW model.
     
    Last edited: Apr 11, 2008
  10. Apr 11, 2008 #9

    marcus

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    Thanks Jennifer, that is certainly correct! And it supplies further justification for what I was trying to get across. We have been thru this several times already. simply because the "big bang" early universe contains very dense regions does not mean it contains black holes or is contained in a black hole.

    However to be fair to the original poster, in the non-expanding case, a region with sufficiently high density WILL collapse. He's got that part right :smile:.
    It is just that you can't insert that into the FRW picture of the early universe.
     
  11. Apr 12, 2008 #10

    wolram

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    We lack the single most important fact to have any idea if any model of cosmology works, a physical measurement, in my opinion cosmology is just hand waving without one.
     
  12. Apr 12, 2008 #11

    Chronos

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    Early universe models do not behave 'classically'. Inflation has no observational parallels in our current universe. The laws of physics may not have been fully emergent in the 'beginning' allowing events not currently permitted.
     
  13. Apr 12, 2008 #12

    wolram

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    And the lady with the bulging shopping trolley beats you to the single item isle, quantity is no substitute for quality.
     
  14. Apr 12, 2008 #13

    jal

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  15. Apr 13, 2008 #14

    Chronos

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    Your point escaped me, wolram.
     
  16. Apr 13, 2008 #15

    Wallace

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    And me. I'm not sure if you missed the last 80 years of physical measurements in cosmology!
     
  17. Apr 14, 2008 #16
    Not the early universe

    It is obvious that the gist of my question was not clear. I am talking about the expansion of the universe reversing and compacting. This compaction should result in the 'mother of all black holes' which is probably much larger than original volume of the early universe. Once all matter is collected in this black hole, will there be a rebound?
     
  18. Apr 14, 2008 #17
    Sorry for the confusion, So far there is no evidence "I know of" for the Big Crunch. The univers is expanding at a increasing rate! If there is enough matter in the Universe eventually gravitaional forces will stop its expansion. When this happens gravity will cause the universe to reverse its direction and begin to collapse under its own weight. This phase of the Universe's life is known as the Big Crunch.
    Eventually all of the matter in the Universe will collapse into a super dense state and possibly even collapse into an unimaginably massive black hole. Some theorize that the Universe could collapse into the same state that it began as and then blow up in another Big Bang. In this way the Universe would last forever but would continually go through these phases of expansion and contraction, Big Bang and Big Crunch and so on...
     
  19. Apr 16, 2008 #18
    Yup, thats how I see the universe, on a continual cycle of Bangs and Crunches.

    Maybe each time it happened more matter was converted from energy to get to what it is today, a lonnggg expansion that only just gets to contract?
     
  20. Apr 17, 2008 #19
    new physics

    Both of the above comments imply that the black hole would [suddenly] expand and disappear. What is the physics for such an occurance?
     
  21. Apr 17, 2008 #20
    I read there's no point one can consider the centre of the universe. The Big Bang started from a singularity of infinite density, right?

    Maybe once it reaches a critical mass, i.e. all the matter in the universe, gravity (or another force) becomes repulsive. Feel free to enlighten me :)

    One thing I'd like to know, is how the maths cope with zero mass particles and infinite properties.
     
    Last edited: Apr 17, 2008
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