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If the strength of gravity levels off, could black holes be unphysical?

  1. Mar 12, 2010 #1
    In GR, the strength of gravity goes to infinity at singularities.

    But what if in nature, gravity increases up to a certain cut-off, and does not continue to increase. If the cut-off is sufficiently low, could it be gravity is not strong enough to overcome pauli exclusion principle, and therefore, a neutron star or something similar cannot form black holes?
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  3. Mar 13, 2010 #2

    Vanadium 50

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    I'm not sure where you are going with this. Your question seems to be "if gravity were weaker, would it act weaker?".
  4. Mar 13, 2010 #3
    I think he's asking if there's an upper limit to how strong gravity can be. If that's the case then the answer is no.
  5. Mar 13, 2010 #4
    yes I'm wondering if there is an upper limit on strength of gravity.
    no as in no black holes? Perhaps a new state of matter results beyond neutron stars.
  6. Mar 13, 2010 #5

    Jonathan Scott

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    Within the geometrical approach of General Relativity, this is a bit like asking whether there is a maximum value to the tangent of an angle - there obviously isn't!

    I personally think black holes probably don't exist. I find it much easier to believe that General Relativity isn't quite right in that sort of extreme case than to believe in the weird physics claimed for black holes, especially given various unsatisfactory theoretical aspects of GR (such incompatibility with QM and Mach's principle and a failure to provide a practical model for overall conservation of energy) and the fact that it fails to explain the universe on a galactic or cosmological scale unless supplemented by dark matter and dark energy. There are also some experimental results which are difficult to explain within GR without bending existing theory to its limits (such as apparent intense intrinsic magnetic fields around quasars and relativistic jets).

    It's even been suggested that GR itself doesn't necessarily lead to black holes without additional assumptions about constants of integration and/or boundary conditions first made by Hilbert (and it's certainly true that Schwarzschild's paper describing his original solution made different assumptions). I've not been totally convinced by arguments on either side here, which appear to amount to "my assumption makes more sense than yours" rather than any sort of proof, but perhaps experimental results will eventually prove it one way or the other.

    In the mean time, I keep seeing references to "massive black holes" being found by astronomers. This is very irritating. What they are actually finding is usually supermassive objects which are extremely luminous in at least some part of the spectrum - about as far from black as one could get! According to the usual (Hilbert) interpretation of GR, these are theoretically expected to have undergone gravitational collapse, but I've not heard of any direct evidence that this has in fact happened. In the case of stellar-mass black hole candidates, there are certain types of X-ray emission from the surfaces of dense stars which are absent in certain cases, and this could perhaps be due to there being no surface, due to gravitational collapse, but there are plenty of other possibilities too.
  7. Mar 14, 2010 #6
    I was thinking along QCD where shorter distances, the strong force gets weaker. Also, there may be conflicts between QM and GR that black holes are an unphysical extrapolation.
  8. Mar 14, 2010 #7


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    (Forgive me if my paraphrasing leads to an incorrect interpretation of your post.)

    What other possibilities? Do you have some ideas about what scientists are seeing when they look for example at Cygnus X-1?

    The possibilites would have to be backed up by plausible models.
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