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Answer to einsteins paradox

  1. Mar 25, 2009 #1
    an atom goes through a particular nuclear reaction and emits a left-handed and right-handed particle. after the particles have traveled to opposite sides of the universe, if you measure the handedness of one you instantly know the other's which is information moving faster than the speed of light. what was the answer to this paradox?
  2. jcsd
  3. Mar 25, 2009 #2


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    I believe you are referring to the EPR paradox (Einstein is the E, Podolsky and Rosen are the other 2). The short answer to the paradox is that their intuition about reality did not hold up. They thought that QM could not be a complete theory because it led to "spooky" predictions. However, modern tests show that these spooky things happen.

    I might point you to my page on Bell's Theorem which discusses the 1935 EPR paper.
  4. Mar 25, 2009 #3
    That's one way of looking at it.

    EPR's conclusion was that the quantum theory was an incomplete theory of physical reality -- and, depending on what one takes 'physical reality' to mean, then it either is or isn't. For EPR, physical reality included a causal reality underlying instrumentation and detection -- and in this sense quantum theory is an incomplete theory of physical reality.

    But quantum theory includes everything that's known wrt the physical reality revealed to our senses via the instrumental data. So, wrt that physical reality it's a complete theory. It accurately predicts statistical probabilities and correlations without a complete accounting of the underlying dynamics.

    If by "modern tests show that these spooky things happen" you mean that quantum experimental phenomena are somewhat mysterious in that the underlying structures and causal dynamics are not fully understood, then I agree. If you mean that 'instantaneous-action-at-a-distance' and/or ftl propagations have been experimentally demonstrated, then I disagree.

    There's no paradox because as far as anybody knows there's no information moving faster than the speed of light.

    For each individual biparticle emission trial:
    If you know that the filters-detectors are aligned, then if you know the result at one end of the universe, then you can deduce (~instantaneously) the result at the other end.

    If you don't know how they're aligned, or if you know that they're not aligned, or even if you know how they're not aligned, then if you know the result at one end of the universe, then all you can say about the result at the other end is that it has 1/2 chance of being a detection and a 1/2 chance of being a non-detection.

    For accumulations of large numbers of individual trial results:
    If you know how they're not aligned, then the accuracy of the qm prediction regarding the frequency of coincidental detection increases as the size of the data set increases.
    Last edited: Mar 25, 2009
  5. Mar 26, 2009 #4


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    I think the OP needs a starting point on the subject before getting into the interpretations. I wasn't trying to make any comment on those by using the word "spooky".

    OP: Learning about EPR, Bell and Aspect would be a good starting point for you before continuing the discussion. Googling those terms should be a good start too.
  6. Mar 26, 2009 #5
    Physical reality is what exists independent of our possibility to observe it. QM does not even make claims what is this reality. Is the wave function real or not? What else, if anything, is real too? These questions are simply not answered. Thus, it does not make sense to claim that QM is in some sense a complete description of reality.

    In realistic theories, we make guesses about it (all our theories are such guesses, so there is nothing wrong for a theory being understood as a guess).

    What "everybody knows" is not relevant.

    Fact is, there are simple realistic explanations of the violations of Bell's inequality in terms of realistic hidden variables and hidden FTL information transfer. But there is no realistic explanation of the violations of Bell's inequality without FTL. Moreover, we have a theorem, that there cannot be such explanations without FTL.

    This is the ideal situation of falsification of a theory. No theory can be falsified in a more rigorous way. Instaed, usually almost every theory can be saved, given some falsification, by some (at least formally realistic) ad hoc explanation. But here there is no such ad hoc explanation - no realistic explanation is possible in principle.
  7. Mar 26, 2009 #6
    No single-history realistic explanation is possible,
  8. Mar 26, 2009 #7
    MWI is something I do not count as an explanation. As well as "God's will is unexplanable". (Is there a difference between the two?)
  9. Mar 26, 2009 #8
    It is newbies question so its is not the place for MWI vs CI.
    I just wanted to say that based on the recent polls, MWI is now #1 - the mainstream interpretation, or at least it is as popular as CI, so you can hate MWI if you want, but lets play fair and give info about all interpretations.

    You need to sacrifice something: determinism, realism, causality, single history. If you can sacrifice single history then you can use MWI - it is realistic and deterministic, and only sacrifice is a single history.
  10. Mar 26, 2009 #9
    Hey Dmitry, I wonder which polls you are referring to, and what demographics of the physics community they represent, because MWI is surely not the most accepted interpretation in the enitre working physicist community. I'm aware of a single poll from a specific sampling of theorists that gives this result and several others that give opposite results, with MWI placing second and even last. I'm just say the MWI adherants should guard against being overzealous.
  11. Mar 26, 2009 #10


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    I suspect the real #1 'interpretation' is the one I adhere to: the "Who the heck needs a damn interpretation?" interpretation.
  12. Mar 27, 2009 #11
    That interpretation already have a name:
  13. Mar 27, 2009 #12

    There was also a poll on this forum in 2005 but I dont remember exactly the name of the thread - I tried to find it but got too many results...
  14. Mar 27, 2009 #13
    You don't need to sacrifice anything from your list: The pilot wave interpretation is deterministic, realistic, causal, and has a single history.

    What is sacrificed is not in your list: It is the speculative idea of Minkowski that a particular symmetry, which appears as an effective symmetry in every wave equation, should be fundamental.
  15. Mar 27, 2009 #14


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    Is there a theorem that proves this statement? I don't think so because there is a counterexample to this (Bohm).
  16. Mar 27, 2009 #15
    Ooops, I forgot about it - for me this is worst interpretation: pure handwaving, plus even not relativistic. I was thinking it had been proven to be false a long tie ago:


  17. Mar 27, 2009 #16
    Sorry, I forgot to add "hidden variables-free"
  18. Mar 27, 2009 #17


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    This is nonsense. The measurement of motion of the muon disturbs the MUON, so the Bohm model predicts that the muon moves when its motion is measured, in agreement with experiments.
  19. Mar 27, 2009 #18


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    First, as I repeated many times, it can be made relativistic. Second, I don't know what do you mean by "handwaving", but all new features of Bohmian mechanics are strictly DERIVED from postulating one additional EQUATION. If you call it "handwaving", then all the best theories in physics are "handwaving" too.
  20. Mar 27, 2009 #19
    No, you just measure the lifetime of muonium, you dont measure the muon itself.
  21. Mar 29, 2009 #20
    Of course, not. Have you ever heard about such things like equivalence theorems? There is one which proves that the predictions of pilot wave theories in quantum equilibrium agree with the predictions of standard QT.

    Note, this is not handwaving, but a theorem. The only nontrivial assumption used there is that the pilot wave beables allow to distinguish macroscopically different states.

    And the "not relativistic" is also only pure polemics. There are a sufficient number of variants of pilot wave theories for relativistic field theory. With the same equivalence proof working as well.

    Whenever you meet some claim about "BM falsified by observation": Crackpot alert. There is a theorem of equivalence with QT. So, the title would be (if BM would really be falsified) "QT falsified by observation". If a paper claiming experimental differences does not explain in detail what is wrong with the equivalence theorem, it should be put into the folder with trisections of angles, quadratures of the circle, perpetuum mobile constructions and other constructions which violate well-known theorems.
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