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Could a black hole "pump"?

  1. Sep 10, 2014 #1
    Hello Everyone,

    This is my first post, I hope I've picked the right forum for this question.

    Could a black hole be "pumping" space/time/matter back into the quantum foam?

    I guess this is asking could it compress whatever falls into it down past plancks constant?
  2. jcsd
  3. Sep 10, 2014 #2


    Staff: Mentor

    Welcome to PF!

    The short answer is we don't have a theory of quantum gravity and so can't know what happens beyond the event horizon of a black hole. Any explanation would be purely speculative.

    As far as we know the smallest quantum unit is planck length and so I would guess thats the limit of compressibility.

    We do have some understanding that black holes evaporate meaning that eventually the matter inside will come back out and you can read about it here:

    Last edited: Sep 10, 2014
  4. Sep 10, 2014 #3


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    Gold Member

    As far as I am aware, a Plank length is a man-made construct, like the meter, the second and so forth and does not constrain the universe in any way.

    Since a Plank length is something like 20 orders of magnitude smaller than anything we can measure now, it's a bit hard to tell for sure. I HAVE read that it is the smallest length that can be measured, even theoretically, but that's a measurement problem, not a constraint on reality.

    I am merely parroting what I have read on this and do not have any real knowledge of the physics involved in making that determination, so it would not stun me to find that I am wrong, but I would surprise me.
  5. Sep 10, 2014 #4


    Staff: Mentor

    That's not really accurate; for a black hole that's large enough, spacetime at the horizon is still well within the classical regime--i.e., spacetime curvature is small enough that quantum corrections should not be important. Only when you get close to the singularity does the curvature get strong enough that quantum effects have to come into play.

    There are speculations about quantum effects like "firewalls" that would come into play at the horizon even if the spacetime curvature were still weak there. However, these are speculations; I don't think they justify making a blanket statement that we need quantum gravity to extrapolate anywhere beyond the event horizon.
  6. Sep 10, 2014 #5


    Staff: Mentor

    I'm not sure what that means. Is this something you've read about, or are you basing it on something you've read? If so, a reference would be helpful.

    I assume you mean the Planck length. We don't really know without a theory of quantum gravity, and I'm not sure there is even a single "best guess" view at this point. Some physicists appear to think that the Planck length is just a "natural" unit of length, but doesn't constrain the physical size of objects, so it would be perfectly possible in principle to compress something to be smaller than the Planck length (though it would probably be very difficult in practice). Others appear to think that the Planck length is an actual minimum possible length, so that lengths smaller than that would have no physical meaning. We won't know for sure until we have a theory of quantum gravity.
  7. Sep 10, 2014 #6
    Hello Peter,

    Thanks for your reply.

    Nope nothing I read about. Just some thoughts I've been having in relation to dark energy and where maybe it comes from. I was thinking that the multiverse (if that is in fact real) could be some closed loop system where energy is channeled via black hole (gravity at its best) => sub planck length quantum foam (dark energy).
    Where this "channel" connects across other or possibly the same universe with in the multiverse.

    Apologies, yes I meant plancks length.

    Looks like I'll be doing some more investigation into Quantum Gravity.
  8. Sep 10, 2014 #7


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    Staff: Mentor

    Please do remember the PF rules about speculation and personal theories...
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