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B Kim et al, 1999 experiment and causality

  1. Dec 7, 2017 #21
    Thanks again! =) so, there's no intuitive way to a lay person to understand the relation exposed in the Kim 's experiment other than the obvious wrong retrocausal intuition. So, if I start studying calculus and quantum mechanics, in about five years or so, I will look into an equation and say "man, it's obvious now that I don't need retrocausality to explain why this happened"!

    Is that it?
  2. Dec 7, 2017 #22
    Thanks a lot Zonde! I will read all the material you pointed! =)
  3. Dec 7, 2017 #23


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    There is nothing more to learn that will help you to rule out the possibility of retrocausal/time symmetric/observer dependent interpretations/models. No one actually knows the underlying physical structure. Strilanc, for example, is correct that QFT describes what occurs as best possible. But this is clear: The context of many quantum experiments explicitly includes the choice of measurement basis by an observer in the future. You get the wrong answer otherwise!

    Whether or not this means anything "flows" from the future to the past is pretty much philosophical past that. But the future does figure into the equation, even if nothing "retrocausal" occurs. In the quantum world, there is no classical causal order.

    There are a number of time symmetric and acausal interpretations of QM that are viable. There is nothing that selects these over other interpretations past your personal preference.
  4. Dec 7, 2017 #24
    It's all subtle a bit.

    I already provided you with some sort of causal explanation, i.e. the point on which the first photon was detected determines the probabilities of the other photon hitting D1 or D2. On this level it should be clear that retrocausality may be avoided and this level of understanding may be supported either by understanding how QM equations work for this particular case or may be (?) with some intuitive explanation on some more popular level.
    Now, whether the situation with entangled particles, including their behavior in Kim's experiment is REALLY understood - is a different story. I.e. it is not clear what is "under" these equations, "No one actually knows the underlying physical structure" (DrChinese). We just know that equations are working and they do not imply retrocausality (nor causality, btw, even though I "used" it in my explanation). What natural phenomena stays behind all this, whether it includes causality, retrocausality, time and space at all - is an open question.

    So in the end you may still remain without true understanding of this stuff, just on some higher level where you'll see that the old-fashioned notions of wave vs particle behavior and attempts to understand QM experiments with their help are a bit naive.
    Last edited: Dec 7, 2017
  5. Dec 7, 2017 #25
    You are wonderful! All of you that helped me! Helping a total stranger gets a better understanding of our reality without asking for nothing in return.

    Besides everything we see on the media that shows how bad human nature can be (wars, corruption), things like sharing knowledge without asking nothing in return shows how beautiful human nature can be!

    Thanks again everyone!
  6. Dec 8, 2017 #26


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  7. Dec 8, 2017 #27
  8. Dec 12, 2017 #28


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    You don't have to think of any 'thing' moving backwards in time when discussing retrocausality. The idea that present outcomes depend on future boundary conditions is probably best understood adynamically as a pattern in the block universe. That is, block universe explanation trumps time-evolved explanation, so while most phenomena accommodate time-evolved explanation, there are some phenomena better left to the more fundamental block universe explanation. Here is an Insight on retrocausality I wrote a couple years ago https://www.physicsforums.com/insights/retrocausality/. This followed a 5-part series entitled "Blockworld and Its Foundational Implications" that starts here https://www.physicsforums.com/insig...time-dilation-length-contraction/#toggle-id-1 . In that series you'll find many examples of the power of adynamical explanation. That series was the precursor for an entire book written on this subject for Oxford UP that is due out in Feb 2018 https://www.amazon.com/Beyond-Dynam...sr=8-1&keywords=beyond+the+dynamical+universe. My point is that viewed adynamically, retrocausality is perfectly reasonable -- we just have to give up our dynamical bias.
  9. Dec 13, 2017 #29
    Thanks a lot Ruta! I will look into that and post my impressions! I'm gonna start reading it right now!

    I've been watching some the Feymanns introductory lectures and I'm trying to understand the Schrodinger equation and I've got an idea, and I would like that my forum friends tell me if I'm in the right direction or the wrong one.

    Here it is, as the photon is fired, there is an equation that could have many limited numbers of solution. But there's no solution to that equation that the photons could reach detector 0 in the "particle only" spot and his entangled pair reach the "don't know which way" detector, so the photon simply doesn't do that.

    I say that because, as far as I know, Schrodingers equation allows many solution to a given quantum state, but many of that solutions has such a low odd of happening that it's irrelevant. Also, there are some impossible solutions, like the idler photon coming to Brazil and hitting my eye.

    Am I in the right path?

    Thanks! =)
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