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I What happens to the stuff that enters a black hole?

  1. Nov 25, 2017 #1
    I've read some articles about Hawking radiation, The holographic principle and obviously I'm well aware of the law of conservation of energy. Is there any research up to date that points toward a possible answer? Is Hawking radiation really a thing? Is it possible for matter/anything to actually escape a black hole? The thought of that if something enters a black hole it's gone forever, seems vague to me. I don't believe it. Wouldn't it break the law of conservation of energy?
  2. jcsd
  3. Nov 25, 2017 #2
    Another way it is looked at is "information", as in:
    Black hole information paradox
  4. Nov 25, 2017 #3


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    nothing that passes the event horizon and goes into the black hole leaves the black hole ... it all adds to the mass of the black hole and the black hole grows in size
    Hawking Radiation doesn't come from beyond (within) the event horizon. It comes from photon interactions near the event horizon




  5. Nov 25, 2017 #4


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    Hawking radiation is very likely a thing. We have never actually observed it, but we weren't expecting to because all known black hole candidates are large enough that their predicted Hawking radiation will be undetectable (in fact, they are net absorbers of energy - the outgoing Hawking radiation is much smaller than the incoming heat from the cosmic radiation background, even though the CBR is only a few degrees above absolute zero). However, Hawking's calculations are quite convincing and there's no reason to doubt that they're right and the Hawking radiation is there even though we can't yet detect it.

    It's not gone forever, it's just beyond our reach forever. There's no violation of energy conservation here because whatever mass/energy falls into the black hole still exists, just not where we can reach it.
  6. Nov 26, 2017 #5
    Okay. With that being said, is it possible that two connected black holes might be the entrance/exit of a wormhole? If not, do they ever disappear?
  7. Nov 26, 2017 #6


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    There is no such thing as two "connected" black holes. You either have one black hole or you have two black holes (which, if they are anywhere near each other, will eventually become one black hole).
  8. Nov 26, 2017 #7


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    I believe that the expectation is that black holes will eventually evaporate through Hawking radiation. We need to wait until the CMB has cooled to below the temperature of the black holes, though, which is far longer than the current age of the universe.
  9. Nov 27, 2017 #8
    What I meant by "connected" black holes, was actually "entangled" black holes.
    What I should've wrote earlier: is it possible that two entangled black holes might be the entrance/exit of a wormhole?

    Last edited: Nov 27, 2017
  10. Nov 27, 2017 #9
    Meaning: We may never find out?
  11. Nov 27, 2017 #10


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    There's nothing in the geometry of the universe that supports the concept of "connected" or "entangled" black holes. And, although you can play about mathematically with "wormhole" geometries, these require negative energy density, which again is in the realm of science fiction.
  12. Nov 27, 2017 #11


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    Not with stellar mass black holes, no. Smaller mass holes are expected to evaporate faster, but I don't think we know any way for them to form. I'm not an expert, though.
  13. Nov 27, 2017 #12
    Agreed. The whole concept seems impossible/far fetched. Who knows, maybe we'll figure something out?

    I guess we're back where we started.

    a) We don't know any way for smaller mass holes to form (?)
    b) We may not live long enough to experience the "collapse" of a stellar mass black hole.

  14. Nov 27, 2017 #13


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    I'm not sure the concept is so far-fetched, but it doesn't follow from the observed and theoretically predicted nature of our universe. The mathematics of GR and black holes is not simple, but it's not that complicated either. There's nothing in that theory that suggests that you would emerge from a black hole somewhere else.

    If you could dig a tunnel through the Earth, however, you would come out on the other side. That is consistent with our model of a spherical Earth.

    Physics is about finding a model for what we already know and then trying to make new predictions with that model. There is some guesswork involved but it's generally focused rather than entirely speculative.

    One of the Feyman lectures on "Seeking New Laws" might be worth watching:


    In fact, his opening words are about "how one goes about guessing". This might be useful in understanding the difference between scientific speculation and science fiction.
  15. Nov 27, 2017 #14
    I'll look into it. Thanks.
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