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Insights How I Stopped Worrying and Learned to Love Orthodox Quantum Mechanics - Comments

  1. Aug 30, 2017 #1

    Demystifier

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  2. jcsd
  3. Aug 30, 2017 #2
    Nice article. Thanks!
     
  4. Aug 30, 2017 #3

    Physics Footnotes

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    Thanks for the stimulating read. I too have come to the conclusion in recent years that anyone serious about the Foundations of Physics must thoroughly acquaint themselves with Bohmian Mechanics; not necessarily because it will turn out to be correct, but because it provides the most coherent and well fleshed-out alternative to the usual bare-bones view of QM.

    I find your idea of taking QM as fundamental, while QFT as emergent, particularly interesting, except for one thing. You talk of non-relativistic particles, but I'm not sure how such things could exist, since we know spacetime, even locally, is not Galilean. Wouldn't the fundamental theory, in your assumed view, have to relativistic QM rather than non-relativistic? To put it a different way, how could we have particles existing in the world which respect Galilean spacetime, but not Minkowskian spacetime, when the latter is the one we know to actually be the case (or at least to be closer to the truth than the former)?
     
  5. Aug 30, 2017 #4

    atyy

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    Are you worried about the chiral fermion problem, which seems to me the remaining problem in realizing the standard model using non-relativistic QM?
     
  6. Aug 31, 2017 #5

    Demystifier

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    I consider it to be a technical problem, with some proposed solutions already existing. So I do not worry too much.

    But I would still like to see your insight article about the chiral fermion problem. Any chance that you write it down one day? :smile:
     
    Last edited: Aug 31, 2017
  7. Aug 31, 2017 #6

    Demystifier

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    What we know is that spacetime does not appear Galilean at "large" distances (e.g. distances much larger than the Planck distance). How does it appear at very small distances, we don't know that.
     
  8. Aug 31, 2017 #7
    "What does have Bohmian trajectories are some more fundamental particles..."

    Above, at, or below string level?
    Multiples of multiple types?
    Multiples of one type?
    One each of multiple types?
    One only of only one type? It would have to really get around, but how elegant.
     
  9. Aug 31, 2017 #8

    zonde

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    Well said.
     
  10. Aug 31, 2017 #9

    zonde

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    It is interesting that possibility of relativity principle not being fundamental is generally not considered.
     
  11. Aug 31, 2017 #10

    Demystifier

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    There are 3 possibilities:
    1) String theory is wrong. In this case the hypothetical fundamental distance ##l_{\rm nr}## at which Nature starts to look non-relativistic is not related to the string scale ##l_{\rm string}##.
    2) String theory is correct, but only as an effective theory. In this case ##l_{\rm nr}\ll l_{\rm string}##.
    3) String theory is correct as the fundamental theory of everything. In this case my theory is wrong and there is no such thing as ##l_{\rm nr}##.

    Sorry, I don't understand the questions. Any hint?
     
  12. Aug 31, 2017 #11

    Demystifier

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  13. Aug 31, 2017 #12

    atyy

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    I think a variant of (2) is that string theory is correct only as an effective theory, but when string theory fails, there is no more spacetime, so ##l_{\rm nr}## does not exist, eg. gauge/gravity where the gauge theory is emergent from non-relativistic QM.
     
  14. Aug 31, 2017 #13
    Sorry, what I meant was have you excluded any of these possibilities for the more fundamental particle(s) ?

    Multiple particles of multiple types?
    Multiple particles of one type?
    One particle each of multiple types?
    One particle only of only one type?
     
  15. Aug 31, 2017 #14

    Demystifier

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    Sure, in principle 2) has an infinite number of versions, including this one.
     
    Last edited: Aug 31, 2017
  16. Aug 31, 2017 #15

    Demystifier

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    I still don't understand what do you mean by "one particle". That the whole universe contains only one particle? That's excluded.
    Concerning the number of particle types, I cannot exclude any possibility.
     
  17. Aug 31, 2017 #16
    Isn't that strings in a nutshell?
     
  18. Aug 31, 2017 #17

    Demystifier

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    No. For instance, a string can split into two strings.
     
  19. Aug 31, 2017 #18

    vanhees71

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    What I find not so convincing about the final conclusion of the article is the fact that obviously nature is not Newtonian but relativistic, as is shown also in the domain of physics, where classical approximations are valid. There seems to be really a limiting speed, ##c##, and it seems to be universal no matter of which system is studied.

    Of course, you have also in non-relativstic (condensed-matter) physics quasiparticles with relativistic dispersion relations and a lot of quite "exotic" features (Weyl fermions, magnetic monopoles, anyons ans what not has been discovered in the sense of quasiparticles but seem not to exist on a fundamental level), but these are only valid in the quasiparticle approximation and in fact describe collective low-energy excitations of the matter as a whole. At some point the non-relativistic approximation breaks down, and you have to use relativistic models.
     
  20. Aug 31, 2017 #19

    Demystifier

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    It seems, but we don't know if this persists at even smaller distances than available by current experimental technology. The default hypothesis is that it persists, but a hypothesis that it doesn't is also legitimate and Bohmian mechanics is not the only motivation for such a "heretic" hypothesis. See e.g. Horava gravity.
     
  21. Aug 31, 2017 #20

    vanhees71

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    Well, I don't see any merit of Bohmian mechanics to begin with. It just assumes unobservable "trajectories" in non-relativistic QT and otherwise predicts the same thing as QT in its minimal quantization. So this argument doesn't convince me too much. I've to check out what Horava gravity might be.
     
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