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B Can QM interpretations be reconciled?

  1. Feb 3, 2016 #1
    Is there already consesus in the (mainstream) scientific world that the various interpretations of QM can't and won't be reconsiled? (unless, perhaps, they find a completely different mathematical framework?)

    And what is the cause of that? :smile:
     
    Last edited: Feb 3, 2016
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  3. Feb 3, 2016 #2

    jfizzix

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    There is at least consensus as to the predictions of quantum mechanics, and we can use it to predict the results of many experiments to surprising accuracy.

    However, since the interpretation of quantum formalism is tied up in philosophical debates in the foundations of science transcending quantum mechanics (such as, whether a Bayesian of a Frequentist interpretation of probability is more sound), I don't think we will ever have a broad consensus as to precisely what relation our mathematics has on elementary properties of the real world (beyond the minimalist stance that we can use it to calculate things we want to know).

    Rarely, but occasionally, someone actually derives a testable consequence of a particular kind of interpretation, and in doing so, we can sometimes rule out certain interpretations. In particular, the experimental violation of Bell inequalities rules out local hidden variable interpretations of quantum mechanics.
     
  4. Feb 3, 2016 #3
    Suppose there would be found an entirely different interpretation covering all others, perhaps accompagnied by a slight change in math. Would such a thing be conceivable?
     
  5. Feb 3, 2016 #4

    jfizzix

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    It is conceivable that we could find a better model for physics than quantum mechanics (i.e., give more accurate predictions), but interpreting this new trans-quantum formalism may well be at least as difficult as interpreting standard quantum mechanics because the interpretation has to make sense of the same experimental data (such as the diffraction and interference of atoms).
     
  6. Feb 3, 2016 #5

    Strilanc

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    The extra details added by interpretations are mutually contradictory. Collapse says only one outcome survives, many-worlds says all the outcomes continue to be tracked.

    The closest thing to an interpretation covering all of them is their intersection: the raw math of quantum mechanics. The "shut-up-and-calculate" interpretation.
     
  7. Feb 3, 2016 #6
    @ jfizzix

    I am thinking of the probabilistic nature of the quantum world; is this probabilistic nature a fundamental property of of the quantum world? With respect to this thread: does the nature of nature prevent us per se (in any case) of knowing certain things about it? And consequently, does this uncertainty dictate (limit) the theories we develop about it?
     
  8. Feb 3, 2016 #7
    I heard that expression come along very often. :wink: Does that mean that the math of QM is so good, that we don't want nor need a different one? Or: is it (almost) self-evident, logical, symmetrical, etc.? I am really wondering about this, for as a layman, it all seems so complicated! :wink: And your answer to that would really help me a lot! :smile:
     
  9. Feb 3, 2016 #8

    jfizzix

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    Thus far, we have never seen an experimental measurement that contradicts the predictions of quantum theory. This doesn't mean the current formulation of quantum mechanics is manifestly "correct", but only that it fits the data we see from the situations we've been able to look at. In more extreme situations (ultra high energies, black holes, etc) it may be that our current quantum theory fails to give accurate predictions, and a better theory may lay yet undiscovered.
     
  10. Feb 3, 2016 #9
    So the fact that the interpretations contradict each other shouldn't worry us very much, right? It just occurs to me why the fact that they do shouldn't be a driving force behind developing a consistent and comprehensive theory? (I just don't seem to get it yet :wideeyed: )
     
    Last edited: Feb 3, 2016
  11. Feb 3, 2016 #10

    jfizzix

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    Since the interpretations don't give different predictions of experimental results, there's no need to be worried.

    Somehow, physicists have hit upon "something" that appears to work really well.
    Perhaps someday we'll have a way of integrating quantum theory into a satisfying conceptual model of reality.
    That will be a good day.
    Until then, quantum mechanics will likely be as hard to learn as a foreign language where most of the words have no English translation, so you're stuck going over it again and again until you start getting the gist of what they mean.
     
  12. Feb 4, 2016 #11

    A. Neumaier

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    Yes, the math of quantum mechanics is in an excellent state (if one neglects some yet unsolved problems in quantum field theory that don't affect anything in the interpretation of quantum mechanics). While not self-evident, it is simple, logical, elegant, efficient, and comprehensive, hence has all the attributes something permanent should have.

    Of course it is complicated for someone not well educated in math. But it is not more complicated than any other subject that requires a number of years of concentrated study to be mastered.
     
    Last edited: Feb 4, 2016
  13. Feb 4, 2016 #12

    vanhees71

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    In short: Interpretations are a philosophical or metaphysical issue of pretty little relevance to physics. The physical part is pretty convincingly solved with the just achieved loophole-free Bell experiments. All unanimously lead to the conclusion that local realism is ruled out and quantum theory is correct. The physical part of the quantum theoretical interpretation, i.e., the minimal interpretation is unique and thus the various ideas of metaphysics behind the formalism are very interesting but irrelevant for physics as a science. It's of course of high relevance for philosophy.
     
  14. Feb 4, 2016 #13

    vanhees71

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    I'd say the math of the QM 1 lecture is even simpler than the math for classical electrodynamics. You just deal with a scalar field and with differential operators like the Laplacian. For E&M you need pretty all of the vector calculus and a bit of tensor calculus either. At least when I think back to my undergrad studies the electromagnetics lecture was mathematically more challenging than the QM1 lecture. What's of course way more difficult is the physics, because QT is much more abstract than all of classical physics (point mechanics as well as field theory), where you have a pretty simple one-to-one mapping of the mathematical objects to the physical ones, i.e., the quantities in the formalism are linked to the observables directly via operational definitions ("Meßvorschriften"). This is different in QT: Here you have an abstract level of description in terms of a (rigged) Hilbert space and (unbound) linear operators on it, and the link between these abstract objects and observables in the real world is pretty complicated via the probabilistic meaning of the quantum state.
     
  15. Feb 4, 2016 #14
    I have a layman idea (not a theory!) that I've never seen discussed elsewhere yet. In short it proposes having global realism rather than local realism. Now my question is: is there an interpretation that endorses global realism? (by that I mean that decoherence into macro objects (the universe itself) has to be taken into account considering outcomes of measurements) I hope I am clear enough. I can't share the details, but I'd really like to know is such kind of interpretation exists! :smile:
     
  16. Feb 4, 2016 #15

    Nugatory

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    If by "global" you mean "non-local", dBB is non-local and realistic.
    Decoherence is a prediction of the mathematical formalism of QM, so it happens with all interpretations.
     
  17. Feb 4, 2016 #16
    Thanks!
    But does there exist a model involving spacetime-stamps-labeling (information) when decoherence in the form of entanglement takes place?
     
  18. Feb 4, 2016 #17

    bcrowell

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    It sounds like you're visualizing the wrong Venn diagram here. The intersection of CI and MWI is MWI; that is, the postulates we use for MWI are a proper subset of the postulates we use for CI. Here's a good discussion of that: http://www.preposterousuniverse.com...hanics-is-given-by-the-wave-function-squared/ . Because of this structure, no experiment can disprove MWI without disproving CI as well. In fact, the postulates of MWI are so generic to quantum mechanics that any violation of them (e.g., a violation of unitarity) would probably disprove quantum mechanics in general, including all its interpretations.
     
  19. Feb 4, 2016 #18

    A. Neumaier

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    This is not only specific to the MWI but to all interpretations of quantum mechanics that deserve this name. If there are predictions that differ from canonical quantum mechanics one speaks of a modification of QM (as, e.g., in the Ghirardi-Rimini-Weber objective collapse theory), not of an interpretation in the strict sense.
     
  20. Feb 4, 2016 #19

    stevendaryl

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    I don't actually see a huge difference between the various interpretations. If you start with ManyWorlds, then you can, at any time, make the pragmatic decision to throw away any "possible" world that is not reachable from yours (by "yours", I mean the one that is consistent with your memories). That pragmatic decision looks like a collapse. If you do this purging of unreachable possible worlds every time you make a measurement, what you're doing will be indistinguishable, for practical purposes, from Copenhagen.

    I've heard an argument that Bohmian mechanics can be interpreted via ManyWorlds, as well, where you split up the ManyWorlds according to positions of particles, and then just declare one of those to be "the real world", and the others are only relevant through the quantum potential.
     
  21. Feb 4, 2016 #20
    One difference is that in Copenhagen you can postulate the Born Rule of probability as an additional law beyond the unitary evolution of the state. In deterministic conceptions the probabilities must somehow be derived from "first principles", leading to much debate whether this is possible in MWI, and some debate in dBB as well.
     
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