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I ER=EPR baby steps: causation or not?

  1. Nov 28, 2018 #1

    nomadreid

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    The questions concern the extension of the holographic principle to the identification of a wormhole between two black holes with negative cosmological constant and an entangled pair on its boundary, included in the conjecture known as EPR=ER ( Maldacena, Susskind). I refer to https://www.nature.com/news/the-quantum-source-of-space-time-1.18797 and https://en.wikipedia.org/wiki/AdS/CFT_correspondence.
    My three questions:
    (a) since anti-de Sitter space does not correspond to our physical universe, is this theory meant to be anything more than a handy calculating tool? That is, there would not be any such wormholes in our physical space, so this would not directly explain any physical phenomenon. ??
    (b) The boundary referred to is for anti-de Sitter space, but since it seems no one has figured out how to define a boundary for de Sitter space, then this would be another reason not to extend this correspondence directly to physical phenomena. ??
    (c) OK, given that the correspondence exists. But the entangled pair on the boundary are connected by a non-causal link, where it is meaningless to talk about what would constitute the "between" in the link, whereas the wormhole connection between the two black holes would be a space in which a "between" in which causal links would make sense. How does this discrepancy wash out in the correspondence?
    Any indication for any of these questions would be greatly appreciated.
     
    Last edited: Nov 30, 2018
  2. jcsd
  3. Dec 3, 2018 #2
    Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.
     
  4. Dec 4, 2018 #3

    stevendaryl

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    I don't understand it very well, either. The claim (and I'm not sure whether this is a conjecture, or whether there's some calculation behind it) is that if you could somehow create an entangled pair of black holes in the way that you can create an entangled pair of elementary particles, then the two black holes would be connected by a wormhole. I'm not sure whether the opposite is supposed to be true, as well, that EVERY maximally entangled pair of particles is connected by a wormhole?
     
  5. Dec 11, 2018 at 6:21 AM #4
    I think the big idea here is that "spacetime is made of entanglement" (somehow). I suppose it's like asking what the relationship between space-time and Hilbert space is. Because AdS/CFT gives a relatively tractable version of quantum gravity, questions can be posed and answered there with some precision. Probably there are analogous perspectives on flat space and de Sitter space, but we don't yet possess those perspectives and so don't know how they differ from the AdS case.

    With respect to causality, the wormholes pinch off internally before a signal can get through (although signals from both ends can meet in the interior, they just can't travel from one end to the other), this is part of the correspondence.
     
  6. Dec 13, 2018 at 5:47 AM #5
    A different but related topic - I thought I would mention it here rather than start a new thread - a new description of Schwarzschild black holes and Hawking evaporation in M(atrix) theory, which is an approach to M-theory in flat space (but in an infinitely boosted reference frame) which reduces to second-quantized matrix dynamics. In effect, the NxN matrix describes N 0-branes (along the matrix diagonal) and the strings between them (in the off-diagonal entries).

    String theorists have found it difficult to describe the kind of black holes we believe our universe contains, which form and then completely evaporate. Instead string theory has focused on eternal black holes with no net evaporation. This paper looks like it contains important progress, and the model of black hole microstructure is very intriguing. They liken it to a polytope in which the faces represent bound collections of the constituent 0-branes, and the edges are "a condensate of off-diagonal matrix modes that act as scaffolding". The bound states exchange 0-branes in a chaotic process, space-time is regenerated as evaporation occurs...

    These are rather amazing statements for a string theory paper. It's a bottom-up combinatorial picture more reminiscent of loop quantum gravity... Another notable thing is that it's in flat space, not AdS. There have been many works proposing combinatorial holographic models of AdS space, such as Preskill et al's quantum error correcting codes. This is in flat space for once, and while it's still somewhat heuristic - not completely derived from the fundamental dynamics - it looks quite solid to me.

    They don't cite ER=EPR, but do mention entanglement later in the paper. I haven't ventured that far, but there's numerous tantalizing glimpses to be had. Each bound collection of 0-branes has as many members as there are dimensions of emergent space, the state information includes entangled supergravity polarizations, and the qubit content is built up from these. I don't know when I'll have time to digest this paper, quantum gravity is not my focus, but it looks important (at least for string theory).
     
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