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  1. Jun 9, 2017 #1
    I joined this site because I had questions and wanted to discuss topics on the subject of black holes. Lenny Susskind's lecture of this topic raised quite a few question a and ideas in my mind. I did write my concerns in the comments for the video, but I'll just paste that here as well. Here's the video:

    if someone managed to create a pair of entangled black holes, according to the current understanding of quantum entanglement, the instant you insert anything (including Bob) it changes the state of the black hole and should destroy the entanglement right? so regardless of the "complexity" inside of one of these black holes, it should be impossible to traverse through a pair of entangled black holes. any thoughts?"


    also even if the entanglement isn't destroyed, where would the interior of the wormhole be? is the black hole creating new space? even if the existing space is curved to allow the ER bridge to form, there must be some sort of space in which to propagate through. or is the existing space used and stretched to form the wormhole/bridge? I guess the gravitational forces from a black hole could, in theory, affect spacetime surrounding the respective black holes in a way that could form a bridge or system that would have a delta function in 3 dimensions with no dependence on time. I don't know. let's figure this out


    another thought; if entanglement is either equivalent or related to the ER bridges, could that eliminate the idea of "spooky action at a distance" due to actual physical connections through the ER bridge? or since "complexity" behind the horizon restricts trans-wormhole communication, is it still "spooky action"?

    Help me out...
  2. jcsd
  3. Jun 9, 2017 #2


    Staff: Mentor

    The video doesn't give the actual math, as far as I can see, and your questions can't really be answered without the actual math. Unfortunately, the actual math is quite complicated, and also the math we currently have isn't known to be right, it's speculative, because we don't yet have a good theory of quantum gravity.

    One thing to keep in mind about ER bridges: the classical ER bridge solution has the bridge (wormhole) collapsing too fast for anything to go through it; an object that falls into one side would get stuck inside the black hole and be destroyed in the singularity before it could get out the other side. So whatever mathematical solution is being used in these speculative quantum scenarios, it can't be that one, at least not in its usual classical form. The spacetime diagrams that get drawn look like the ones for the usual ER bridge, but nobody ever seems to talk about how the actual solution must differ in order to allow anything to traverse the wormhole.
  4. Jun 10, 2017 #3


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    That point is actually crucial for the consistency of the proposal. The original system that was being studied is ADS-Schwarschild, and the conjecture is verified in precisely this form (when things are most classical) assuming Ads/Cft. If an observer was allowed to cross the Einstein-Rosen bridge, you would have displayed superluminal signalling and violated the EPR side. Instead the point is that if an observer jumps into one side of the throat, unless he violates the averaged null energy condition, the throat will quickly pinch off before he gets to the other side. Now, what can happen, is that an observer jumps in on one side, and another observer jumps in on the other and they could (at least in the idealized scenario) meet in the interior and compare notes (right before they're crushed by the singularity). However no observer can traverse the wormhole end to end without breaking it.

    The very interesting thing about this proposal is that it is an exact state (called the thermofield double state) that satifies all the conditions for a firewall to appear (as written down in the original AMPS paper) but explicitly doesn't (the two observers comparing notes both agree there was no firewall). It's an idealized but interesting loophole.
  5. Jun 14, 2017 #4
    I get that much. My thinking was that maybe it's the breaking of the entanglement that causes (or is) the collapsing wormhole.
    And another idea (totally speculative) is that the "singularity" inside is the ripping or separating of space. Any insight on these types of ideas? These are just things I thought about but it wouldn't be the first time that I thought I had "theorized" something that had already been being researched for 40 years..... also I think gravity is an emergent property of composite matter. Ill just leave that there....
  6. Jun 14, 2017 #5


    Staff: Mentor

    The "totally speculative" should be a clue that this is not a suitable topic here; personal speculations are off topic per the PF rules.

    If you are asking whether the singularity being the ripping or separating of space is such an idea, the answer is no.
  7. Jun 14, 2017 #6
    Firstly, thanks for posting replies.
    It's not off topic. My original post was a list of questions. I'm still asking questions, not providing answers. The PF rules don't restrict the questions I can ask.

    another question I have is exactly what effect does a singularity have on space itself? I understand that the time dimension is altered in some way inside a black hole, but this one puzzles me.
  8. Jun 14, 2017 #7


    Staff: Mentor

    Look at the quote from your post to which I responded about personal speculation being off topic. It's a declarative sentence, not a question.

    Also, since personal speculation is off topic, asking questions that are based on "totally speculative" ideas you have can become off topic if you do enough of it. PF discussion is supposed to be based on mainstream science, as published in textbooks or peer-reviewed papers. That means the questions you ask are restricted to questions about those things. Questions of the form "is this idea I just came up with something that's already been studied?" can qualify, but it's a fine line.
  9. Jun 14, 2017 #8


    Staff: Mentor

    None. The singularity is a moment of time, not a place in space. More precisely, it's a moment of time that is to the future of every event inside the black hole's horizon.

    This is not the best way to think of it. The best way to think of it is just that, as I said above, once you are inside the horizon, the singularity is in your future no matter what you do. That is why you can't avoid reaching it. But until you reach it, "time" works for you just the same as it always did: your clock runs just fine, your bodily processes continue normally (although as you get closer to the singularity and tidal gravity gets stronger, that will affect the structure of your body--but that's not an effect on "time", it's just ordinary tidal gravity stretching and squeezing you).
  10. Jun 14, 2017 #9

    Zafa Pi

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  11. Jun 14, 2017 #10
    Apparently my original post is somewhat confusing or difficult to understand. What I am trying to do here is better understand these topics through discussion. I have done somewhere between zero and no experiments so there are no theories to be given here. I am simply trying to dissect Lenny Susskinds lectures.
  12. Jun 14, 2017 #11
    @Zafa Pi I read those articles and yes that's pretty much what I was getting at. So this research could, possibly, shed some light on the "spookiness" of entanglement. And maybe even gravity. Do you know of any good sources for new information regarding this topic?

    This interests me as well. I'd like to see black holes and black hole models utilized more often and more seriously than in the past. Black holes were considered science fiction for a long time but they're now being treated seriously. Its crazy how such good physics can come from speculation.
  13. Jun 14, 2017 #12


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    True but irrelevant to the mission statement of this forum, where personal speculation is expressly forbidden. PF is not here to develop new physics but to explain known physics.
  14. Jun 14, 2017 #13


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    The best approach, measuring best as most likely to get you the most accurate description of knowledge to date, is to quote specific snips from the lectures and ask your questions around those specific snips.

    A lot of well intentioned threads end up dead ended either because the poster, not on purpose, is using imprecise language, or the poster is expecting that this is a place to discuss / explore the viability of their own speculations. If you start a question with a specific snippet from Susskind or any quote from a peer reviewed publication, it helps to avoid those potential pitfalls.

    I've started more threads than I'd like to admit that have ended up going nowhere mostly because the language I am using makes sense only to me.
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