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I What is the difference between cfd and realism?

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  1. Dec 29, 2017 #21

    bhobba

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    Its glad to know I am not the only one that feels that way about Bohr. To me his response is - how to express it - a bit mumbo jumbo'ish - like much of Bohr's writings are to me. Maybe its a bit like David Bohm. When he was good he was very very good - when he was, let's say not quite exact as in his implicate order writings, he was - well terrible. In his defense though I think Einstein understood Bohr - his objections were I think more wryly stated when he said - nearly everyone's refutation of it was different.

    Really interesting was when Dirac visited Bohr - totally different in style:
    http://www.ams.org/notices/201109/rtx110901278p.pdf

    Actually to me Dirac was clearer than Bohr.

    Added Later.

    To see what me, Dr Chinese and Vanhees mean see the following:
    https://philpapers.org/rec/WHITEP
    For many years after Bohr's response to the EPR argument, Bohr was considered to have provided an authoritative rebuttal of the ideas of the paper, and more generally of Einstein's stance on quantum theory. More recently, however, there has been great difficulty even in achieving general agreement on Bohr's meaning. Two recent papers, by Dickson, and by Clifton and Halvorson, have sought to establish the structure of Bohr's argument. In the present paper, the papers of EPR and Bohr are re-assessed in the light of these recent papers, and also in light of the development and presentation of quantum information theory.

    Only recently o0)o0)o0)o0)o0)o0)

    Oh dear. I wont spell out what that suggests to me - my respect for the scientists involved is far too great. Suffice to say perhaps similar to Von-Neumann's proof of no hidden variables that everyone seemed to agree with, but hardly anyone took the time to check. Or think about it clearly enough - I didn't know of Bell etc when I read his book - Mathematical Foundations of QM and didn't see the error - bad boy, bad boy :nb):nb):nb):nb):nb):nb):nb).

    Thanks
    Bill
     
    Last edited: Dec 30, 2017
  2. Dec 30, 2017 #22

    vanhees71

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    Sure, Dirac was the typical no-nonsense math physicist. You can take his papers and bind them together to a textbook, and his own textbooks are all masterpieces (not only the most famous one, The Principles of Quantum Mechanics, but also his very brief but concise GR book). In the early days of QT there were indeed these two types of physicists: namely the ones using the math and presenting a physical theory (Born, Jordan, Pauli, Sommerfeld, Dirac, also Schrödinger, but with a flawed interpretation of the quantum state) and the more philosophically inclined type tending to blurr the subject by gibberish statements about some kind of "deeper meaning" of QT (Bohr, Heisenberg, partially also von Neumann, whose interpretational part is completely flawed, while his work on the mathematical foundations of non-relativistic QT is a cornerstone of the theorie's development). Bohm is somewhat in between: On the one hand he has written a very good textbook on the subject (not to mention his original work, including the Aharonov-Bohm effect) on the other hand he has presented his non-local pseudo-deterministic additions, now called "Bohmian Mechanics". I consider this also as flawed since the claimed trajectories of particles are not observable, and anything that is observable is equivalent to standard QT. For relativistic QFT, the Bohmian approach is at least difficult, if not self-contradictory.
     
  3. Jan 1, 2018 #23

    Fra

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    I think there is GREAT value both in cleaning up the mathematical formalisms, AND understanding the constructing principles that led to current formalisms, and that might lead us to improvements in the formalisms.

    I always enjoyed BOTH the more formal "right to the point" books, to learn the theories, and the "behind the scenes" thinking especially of the original founders.
    From the point of view of mastering an established theory you can surely skip what you call "gibberish", and read the "cleaned up" writings. But if you have the ambition to undersand they theory conceptually in order to find the right angle to solve some of the open questions such as unification and quantum gravity, the gibberish of the original founders might well be gold worth as well.

    As I understand it, I think Bohr's point in the 1935 paper is to try to convey why the idea of Einsteins local realism is fallacious when applied to "atomic physics" as bohr calls it. And the reason is complementarity that as per the "quantum of action" that is significant for "atomic physics", and that implies that it is impossible to actually make a proper "preparation" in a way that fulfills the local realist description - without disturbing the system.

    Sure, it is obvious, given history that this is hard to grasp for many physicists. Im my view, Bohr takes the concept of "measurement theory" truly seriously.In this sense i think noone ever was more clear than Bohr. IMO bohr takes on the minimalist stance here, and suggest that if we are to consistently talke about measurement theory, even the "preparation" is a kind of measurement. And there is not really any room for the old style realism. It is fundamentally incompatible with what Bohr thinks is the "essence of QM", and i fully share that view!
    Bohr has an interesting remark in the end of his paper where he compares the "complementarity" with "relativity". I cant tell from that paper alone how deep insight he had about this, but I think that association is probably just the right way to TRY to adress things to Einstein, as beeing the father of relativity in the first place. The possible parallell here is that relativity, with its observer associated frames of reference, conceptually could be expanded to consider more general "observers", where the machian relativity ideas, could well be applied also to measurements.

    Somehow i would be curious to hear what Bohr and Einstein would say about todays situation, and about stuff like "GR=QM", "EPR=ER". I sometimes get the feeling that there in history are "lost ideas" that was just grossly misunderstood by contemporary scientists. After all, people grow old, and even a genious can only do so much progress in a lifetime.

    I suspect that Einsteins take on "realism" would be different today, and probably more reflect the reality of law as opposed to evolution of law. I also wonder what Einstein would think today about the idea that his field equations are to be seen as an equation of state.

    Conceptually these things are all very closely related to the original topic in the epr paper, and its a pity we cant hear their what their opinions today would be. And which should not be hard to understand, these conceptual issues - at this immature point - are not yet clear mathematical problems simply because we do not know (except i know some of you beg to differ) how current theory needs to be deformed or changed in order to realize the presumed vision bohr is hinting at to unifty "complementarity" and "relativity" in the observer-observer sense.

    /Fredrik
     
  4. Jan 2, 2018 #24

    Demystifier

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    "Truth and clarity are complementary."
    - Niels Bohr
     
  5. Jan 2, 2018 #25

    Demystifier

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    For my taste, Duncan is even better than Weinberg. I particularly like how Duncan demystified the Haag's theorem.
     
  6. Jan 2, 2018 #26

    vanhees71

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    I think the problem is that Bohr hadn't a "translator" who transformed his ingenious insights to clear mathematical analyses. For Heisenberg that role has been played by Pauli. Pauli's and Heisenberg's approach to physics and their entire livestyle were indeed "complementary", and together they brougth (quantum) physics a huge step forward, while the entangled pair "Heisenberg-Bohr" amplified the mysticism of each other.
     
  7. Jan 2, 2018 #27

    vanhees71

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    It's not better but fills the gaps in Weinberg's treatment. I've been always a bit mystified about the fact, why Weinberg doesn't even mention the problems addressed by Haag's theorem.

    My present recommendation for how to learn relativistic QFT is

    Start with working through M. Schwartz, QFT and the Standard Model to learn the physics and how to really calculate S-matrix elements, including renormalization. Then read Weinberg's books to understand why QFT looks the way it looks from the point of view of first principles (symmetries + causality requirements) and finally study Duncan for the finer details of the mathematics behind it, including all the trouble with LSZ, Haag, etc.
     
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