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Are Singularities Possible?

  1. Jan 30, 2008 #1
    Hi

    I'm not very clued up on the mathematics behind these things and I tried searching for relevant threads but everything I found was a bit over my head so sorry if this has come up loads of times before but I was hoping someone might be able to explain in simple terms the reasoning behind them.

    Anyway, I've been thinking about singularities and can't understand how they could exist. If you were at the centre of gravity of an object like a collapsing star, or anything else for that matter, you would be weightless. No matter how small the object became there would still have to be a centre of gravity with no net gravitational pull. So how could a singularity ever come about? surely if the centre of a mass has zero gravity
    then singularities are impossible.

    And therefore the big bang can't have come from a single point either, is this correct?
     
  2. jcsd
  3. Jan 30, 2008 #2

    chroot

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    Most physicists feel that singularities are not possible in nature, and simply represent failures in our current models. In other words, most physicists hope that a generalized theory which combines both quantum mechanics and general relativity will eliminate the singularities present in each in isolation.

    - Warren
     
  4. Jan 30, 2008 #3

    marcus

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    that's my impression too, from what I've read and the people I've spoken with. A singularity is the breakdown in the mathematical model used in some manmade theory.
    Where the model fails to compute or gives infinities instead of meaningful answers.

    So I agree with Chroot that hey arent normally considered to be something that occurs in nature----they happen in formulas, mathematical model and stuff like that.

    But Chimps, what are you actually asking? You seem to think that something at the center of a collapsing star wouldn't feel crushed by enormous pressure! You are arguing that because there is no gravity force in any direction right at the dead center.

    If that is what you are saying, you've been misled somehow. A collapsing star (when it forms a black hole) does not actually collapse down to a mathematical point, but the quantum gravity models people study these days have it collapse to something pretty darn small. The pressure would be stupendous.

    The density, or matter per unit volume, doesnt actually go to infinity (as it does in the classic theory's breakdown)---so it is technically not a singularity---but the density is still pretty darn high. I remember that in some quantum gravity computer modeling recently it was going as high as 1093 times the density of water. These results haven't been ruled out. We can't say for sure but it could be that a whole star, when it collapses to BH, gets compressed down to something the size of an ordinary uncompressed atom, which you could think of as for all practical purposes a single point. This is pretty weird and I don't claim to understand how it could be, but it's not ruled out. We have to consider it a serious possibility.

    So even if singularities don't exist in nature, in the sense of points with infinite density, there could still be points where at least momentarily very high density is achieved and the whole material of a star is compressed down into a bewilderingly small space.

    If I am mistaken about this, I hope others like Chroot, SpaceTiger....will correct me.
     
    Last edited: Jan 30, 2008
  5. Jan 31, 2008 #4

    Chronos

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    I'm still voting for the Planck density as nature's limit. Black holes still exist, but, have ponderable properties.
     
  6. Jan 31, 2008 #5

    wolram

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    If this is correct, would it rule out the possibility of white holes?
     
  7. Jan 31, 2008 #6

    marcus

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    I didn't mean to give that impression. I think it is an open question what happens in gravitational collapse.
    In some models there is a bounce: a state of very high density is reached followed by re-expansion (out the back door so to speak) forming a new region.

    So in that case a singularity (a breakdown of theory) is avoided by bounce and re-expansion. But that is not the only model, nor the only possible outcome. There is another case----a guy at Portsmouth in the UK writes about this one---where there is no bounce. The process stops at a state of extremely high, but not infinite, density.

    This could be pictured as a new material, much denser than neutron star material but not infinitely dense. A material, or a condition of space, that we don't have any conception of so far.

    I find it interesting that people using different quantum gravity models come to different conclusions about the result. I hope that differences between the models will also translate into different predictions about observable physics----so that it will be possible to rule all or some of the models out.

    Maybe it will turn out that a bounce can occur in some circumstances and not in others.
     
  8. Feb 4, 2008 #7
    I read all your comments and found them very interesting but nobody seems to have addressed the 'big bang'.

    Working backwards it is the same thing, so why does the big bang carry any weight? Clearly the whole idea is bunk. Unless of course most physicists don't accept an objective universe. So where does that leave us? A virtual universe?
     
  9. Feb 4, 2008 #8

    chroot

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    We don't know all the answers yet, but that doesn't mean our current models are 'bunk.' Are you suggesting that we throw away the model we've spent decades developing and researching, simply because it's not yet done?

    - Warren
     
  10. Feb 4, 2008 #9
    Well, there is the contradiction. On one hand you deny the existence of singularities in nature yet you still want to believe the big bang (singularity) is a valid theory.

    I have no problem throwing it away because I don't think it will ever be 'done'.
     
  11. Feb 4, 2008 #10

    chroot

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    You are quite wrong. The big bang model is currently incomplete, because we lack the physical theory (a generalization of both quantum mechanics and general relativity) to describe it. Most physicists feel that this theory, when it is found, will eliminate the singular nature of the big bang, black holes, etc.

    - Warren
     
  12. Feb 4, 2008 #11
    Yeah I also feel that if the answer is found then the answer will be found. That is pretty darn obvious. Sorry, but constantly repeating that theories are incomplete doesn't get us anywhere.
     
  13. Feb 4, 2008 #12

    chroot

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    What alternative do we have but to recognize the limits of our theories, and continue to refine them with thought and experiment?

    - Warren
     
  14. Feb 10, 2008 #13

    cristo

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    What about Newtonian Gravity? That got us pretty far, but is not a complete theory.
     
  15. Feb 22, 2008 #14
    What exactly does Newtonian physics have to do with this discussion? We are discussing the implications of singularities here.

    The big bang theory, as incomplete as it is, leads us to a very important question. Is the universe objective? according to the big bang theory it can't be. It must be virtual. That is what the big bang implies.

    Why can't the hidden variables in quantum physics be found? The answer could be because the variables are 'on the outside'. The more we learn about the universe the more this seems to be the case.
     
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