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Black Holes : Zero Volume, Infinite Density

  1. Jul 13, 2011 #1
    I didn’t believe it when I first heard it. I don't know how to reconcile this fact with what I understand about the known laws of physics. It appears to be one of the grandest mysteries I can think of. I understand that most of the universe is empty space but zero volume is different. Anyways, here are my thoughts on the subject.

    1) Philosophically, if it has zero volume, how can one say that it even exists? (Aside from the obvious like gravitational effects and the light surrounding). BHs are the polar opposite of what is considered empty, and yet, they're ‘empty’ (or devoid of space/matter) as well. I can’t think of anything else in the universe that has no volume but can still interact with other objects.

    2) Based solely upon my intuition (which doesn't count for much here), I would expect a different outcome from extremely dense collections of mass... i.e. once enough matter has accumulated, rather that imploding into a BH it either idles or EXplodes since it can't handle any more stress.

    3) When you consider that BHs have zero volume, it doesn’t seem to make sense when you compare one with another. BH masses can differ but isn’t that mass really just the accumulation of the mass around it? If so wouldn’t that make all BHs the same size?

    4) Since space-time is expanding more rapidly than light can travel, doesn't this imply that our universe exists within a BH? If so doesn't this hint at the potential fate of the matter pulled into a BH?

    5) Let’s pretend that massive collections of matter don’t form BHs, and instead, blink out of existence once enough mass is present to create one. This would send matter careening out into space away from where the BH would normally form. What I’m wondering is what type of buffering effect a BH has on the universe, specifically on how it alters the rate of expansion/contraction.

    6) Last one… what happens to a BH when it ‘dies’ (if that’s even possible)...? does it revert back to the critical mass required to create one? Or does it just blink out of existence without much of a show?

    Thanks for reading. Comments are welcome.
  2. jcsd
  3. Jul 13, 2011 #2
    well, black holes dont have zero volume. google the schwarzchild radius.
  4. Jul 13, 2011 #3


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    As RK1992 has pointed out Black Holes have a non-zero volume. Gravitational Singularities are usually referred to as having zero volume however as I understand it contemporary thought is that this prediction is a result of incomplete theory. There was a thread about this recently https://www.physicsforums.com/showthread.php?t=511693
  5. Jul 13, 2011 #4
    The schwarchilds radius isn't the black hole itself though, its a length proportional to the mass of the black whole which expresses how far light can't escape. The mass itself of the black hole does not reside inside this radius, it is all concentrated at a singularity with infinity density and zero volume. So the mass of the black hole itself still has zero volume.
  6. Jul 14, 2011 #5


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    I would refer you to my above post. Contemporary understanding is that the zero volume, infinite density singularity model is wrong, for a better understanding we need to develop new science. This is discussed in the thread linked above.
  7. Jul 14, 2011 #6

    i should probably send my old physics teacher an email- although the odds are she knew and was just telling me 'white lies' since the actual answer would have been over my head.

    thanks for your insight i will check out the thread you suggested.
  8. Jul 14, 2011 #7


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    We deal with zero volume items all the time: For example, to the best of our knowledge electrons are point particles with zero radius, yet they have a finite mass. Of course we know that quantum effects conspire to blur the location of the electron so that it occupies a non-zero volume of space - on average. Quantum physics saves the day and calms our fears of the infinite :smile:

    It is suspected that quantum effects are going to do something similar to the singularities at the hearts of black holes, so that the "smooth" physics of classical General Relativity will have to be discarded or at least modified at some scale in the close proximity to the singularity. But it will be a pretty small scale compared to the volume inside the schwarzchild radius. General Relativity should apply quite nicely to the vast majority of the region inside the radius.
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