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Blackholes and entanglement

  1. Jun 21, 2010 #1
    I was watching a show on TV about physics and a question popped into my head that I can't find an answer to. I remember hearing it may be possible to create tiny blackholes in the LHC, so maybe you can test this, I don't know. Here is my question...

    What would happen if you took two entangled particles and put one in your lab and shot the other one into a blackhole? Would you be able to observe what happens inside a blackhole by observing the particle in your lab?
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  3. Jun 21, 2010 #2


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    This is a very good question, and I certainly don't know the answer. Maybe nobody does. Any black holes produced at the LHC would have a lifetime far too short to try the experiment, so I'm afraid that this is a "gedankenexperiment" for now, but I'm fascinated to know if anyone has a proposed explanation for what would happen.
  4. Jun 21, 2010 #3


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    What would you expect to see exactly? It's not like there is any signal to receive.

    I would expect that the interaction of Alice with the black hole would lead to a collapse of her wave function. That would in turn lead to a collapse of Bob's as well. Not a lot to be gained from that, unfortunately.
  5. Jun 21, 2010 #4


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    This is a possible explanation, but why should this happen? We know that an observer passing the event horizon sees nothing unusual, and does not even notice that they have passed the event horizon. Also, the gravitational field at the horizon can be made as low as desired by increasing the mass of the black hole. So what would cause the collapse of the wave function?
  6. Jun 21, 2010 #5


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    OK, then alternately Alice doesn't see her wave function collapsed. And then we measure Bob. No difference in what we see.
  7. Jun 21, 2010 #6

    George Jones

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    A Physical Review Letters paper, Alice falls into a black hole: Entanglement in non-inertial frames, written by I. Fuentes-Schuller and R. B. Mann looks interesting. The paper's last sentence:
  8. Jun 21, 2010 #7
    I am sure there are subtleties associated with entanglement in curved space-time. Still as DrChinese answers' convey, we have no reason to expect anything useful from the experiment. There might be correlations between the results of Alice and Bob according to theory, but if they do not communicate classically with one another, they can't know those correlations experimentally.

    With a horizon between them, although you still have the correlations, Alice and Bob cannot talk to one another and so they cannot measure those correlations. I fail to see why this is a "good question" in this respect. To me this is rather an "academic question".
  9. Jun 21, 2010 #8
    See these:

    Einstein-Podolsky-Rosen correlation in gravitational field

    Authors: Hiroaki Terashima, Masahito Ueda
    Abstract: For quantum communication in a gravitational field, the properties of the Einstein-Podolsky-Rosen (EPR) correlation are studied within the framework of general relativity. Acceleration and gravity are shown to deteriorate the perfect anti-correlation of an EPR pair of spins in the same direction, and apparently decrease the degree of the violation of Bell's inequality. To maintain the perfect EPR correlation and the maximal violation of Bell's inequality, observers must measure the spins in appropriately chosen different directions. Which directions are appropriate depends on the velocity of the particles, the curvature of the spacetime, and the positions of the observers. Near the event horizon of a black hole, the appropriate directions depend so sensitively on the positions of the observers that even a very small uncertainty in the identification of the observers' positions leads to a fatal error in quantum communication, unless the observers fall into the black hole together with the particles.

    The EPR correlation in Kerr-Newman spacetime

    Authors: Jackson Said, Kristian Zarb Adami
    Abstract: The EPR correlation has become an integral part of quantum communications as has general relativity in classical communication theory, however when combined an apparent deterioration is observed for spin states. We consider appropriate changes in directions of measurement to exploit full EPR entanglement for a pair of particles and show that it can be deduced only up to the outer even horizon of a Kerr-Newman black hole, even in the case of freely falling observer.
  10. Jun 21, 2010 #9
    So the correlations may be modified, possibly to the point where they are expected to be completely washed out. But it does not change (if only to make the situation even worse) the primary problem IMHO that the OP does not realize that classroom perfect correlations already can not be used for communication.
    Last edited: Jun 21, 2010
  11. Jun 21, 2010 #10
    Well, there is a possibility that it actually does something quite interesting. Namely, from the point of view of deBB theory, the entangled pair that falls into the event horizon may in fact be thrown out of quantum equilibrium and then superluminally signal its state to the external entangled pair:

    Black Holes, Information Loss, and Hidden Variables

    Authors: Antony Valentini
    "We consider black-hole evaporation from a hidden-variables perspective. It is suggested that Hawking information loss, associated with the transition from a pure to a mixed quantum state, is compensated for by the creation of deviations from Born-rule probabilities outside the event horizon. The resulting states have non-standard or 'nonequilibrium' distributions of hidden variables, with a specific observable signature - a breakdown of the sinusoidal modulation of quantum probabilities for two-state systems. Outgoing Hawking radiation is predicted to contain statistical anomalies outside the domain of the quantum formalism. Further, it is argued that even for a macroscopic black hole, if one half of an entangled EPR-pair should fall behind the event horizon, the other half will develop similar statistical anomalies. We propose a simple rule, whereby the relative entropy of the nonequilibrum (hidden-variable) distribution generated outside the horizon balances the increase in von Neumann entropy associated with the pure-to-mixed transition. It is argued that there are relationships between hidden-variable and von Neumann entropies even in non-gravitational physics. We consider the possibility of observing anomalous polarisation probabilities, in the radiation from primordial black holes, and in the atomic cascade emission of entangled photon pairs from black-hole accretion discs."
  12. Jun 21, 2010 #11
    Re the paper above, see section 2.4 for the specific argument for why quantum equilibrium may not be stable across the event horizon of a black hole.
  13. Jun 21, 2010 #12
    Hidden Variables... hmmph. I don't think this would be useful at all as an experiment. There seems to be some serious drift from the OP's question, which has been answered in the two possible ways: wavefunction go bye bye, or you wait arbitrarily long period of time and nothing changes.
  14. Jun 21, 2010 #13
    Interesting to whom ? In 6 years, the paper has been cited only once by another author than the original one, and this citation is a speculative dissertation on non-locality not even published in a peer reviewed journal either, but in Oriti's collection "Towards quantum gravity". Do you know whether Valentini attempted to publish it ?

    I personally find it entertaining or cute, but certainly unhelpful to the OP.
  15. Jun 21, 2010 #14
    If Valentini's prediction is correct, it would/should be highly interesting to anyone who thinks unitary evolution should be preserved inside a black hole - because it would imply that unitary evolution is not preserved inside a black hole, and it would give us conclusive evidence that hidden variables exist.

    As far as I know, no, not that particular paper. However, he did publish another paper in which he does discuss the same idea (see section 5):

    Astrophysical and Cosmological Tests of Quantum Theory
    Authors: Antony Valentini
    Journal reference: J. Phys. A: Math. Theor. 40 (2007) 3285--3303

    I think it's actually quite relevant to the OP's question, as Valentini's proposal suggests a possible means by which an EPR pair could indeed tell us (via superluminal signaling from a nonequilibrium state inside the event horizon) what is going on inside the event horizon of a black hole. Sure, it's speculative, but no more so than the OP's original question.
    Last edited: Jun 22, 2010
  16. Jun 21, 2010 #15
    From another perspective, this is just placing and pushing for dBB-type approaches where nobody called or needed it.
  17. Jun 21, 2010 #16
    Now I remember this paper. Thanks for pointing that out, since you wish to discuss it, maybe you can enlighten me : considering the uttermost importance of the claims in this paper (namely make of dBB a testable theory instead of a mere difficult interpretation), how come in nearly 5 years nobody quoted it ?
  18. Jun 21, 2010 #17
    While a deBB-based approach may not have been explicitly called for, the fact remains that it suggests a novel and relevant answer to the OP's question. And that, IMO, is reason enough to mention it. Also, don't forget that I initially posted two papers that answer the OP's question using standard approaches to QM and GR. So I've actually presented a diversity of approaches to the OP's question. Also, I think it often gets forgotten that no one particular formulation or interpretation of QM has a monopoly on physics. If someone has a reference which gives a different answer to the OP's question from, say, a Consistent-Histories approach, I wouldn't be opposed to it being mentioned as well (even though I personally don't take Consistent-Histories very seriously).
  19. Jun 21, 2010 #18
    I don't know, that's more of a sociological question, but here are some possible reasons:

    (1) Most string theorists probably think that the holographic principle can preserve unitary evolution across the event horizon of a black hole, and thus they would not be likely to have a reason for considering the possibility of a breakdown of quantum equilibrium.

    (2) Most field theorists are not aware of the existence of nonrelativistic deBB theory, let alone its field-theoretic generalizations (which, by the way, have only really had significant advances within the past 5-10 years).

    (3) Most field theorists probably think that the motivation for hidden-variables is dubious or disproven to begin with (for example because of a misunderstanding of what the violations of Bell's inequalities actually imply); so just by seeing the phrase 'hidden variables' in the title, they might be less inclined to read further.

    (4) Even within deBB theory research, there are people (particularly the Rutgers-based 'Bohmian mechanics' group) who don't think it's fruitful to look for quantum nonequilibrium, who have a personal dislike of Valentini, and who have tried to downplay Valentini's ideas without much critique.

    (5) There might be physicists who disagree with Valentini's arguments, but chose (for whatever reasons) not to write a paper critiquing it.

    There might be other reasons, but those are the ones I can think of off the top of my head. Anyway, this is getting off topic now.
    Last edited: Jun 22, 2010
  20. Jun 21, 2010 #19
  21. Jun 21, 2010 #20
    Thanks for you answers Maaneli, I appreciate.
    Note that my question was genuine, I am really surprised that such an important claim receives so little attention. Hopefully Valentini will take care of testing his ideas, would data become available (there has been recent claims of uncontrolled errors in WMAP power spectrum BTW).
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