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Feynman's New Zealand lecture, Inca astronomy, rule and reason.

  1. Aug 7, 2013 #1
    In Feynman's New Zealand lecture,



    he points out how the Inca Indians were able to predict the motion of major heavenly bodies but did not understand the physics behind these motions (Let us assume that is true. We don't have, as Feynman points out, much recorded Inca history so it is possible they contemplated a sun centered solar system with planets, moons, and other stuff orbiting the sun and may have even come up with Newton's law of gravitation, big ifs).

    I think Feynman pointed out that like the Incas we can predict much experiment, and like the Incas we have no picture (in the spacetime that the experiments occupy) that implies the quantum physics of nature.

    Did Feynman consider such a picture tough or impossible to come up with? I think Feynman answers this question at the one hour, 8 minute mark of the video above, very tough.

    Have any of our best physicists and mathematicians made any stabs at such a picture?

    Any suggested reading would be welcome!
     
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Aug 7, 2013 #2
    Feynman talked a good deal about the "pictures" he and other quantum physicists use to understand quantum theory. (From "No Ordinary Genius" by Christopher Sykes, a sort of compilation of random things by and about Feynman.)

    I guess my feelings would somewhat echo Feynman's: I think in order to understand quantum physics, quantum physicists use a set of pictures which are abstract mathematical pictures similar to the diagrams in math books, along with some pictures of the classic QM experiments (e.g. tunneling, double slit, stern gerlach). But it's sort of a piecemeal picture since you can't easily put it all together into one nice neat master picture of what really goes on in the full formalism of quantum theory.
     
    Last edited: Aug 7, 2013
  4. Aug 7, 2013 #3

    bhobba

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    I think the issue with QM is not so much we cant get an intuitive grasp, and even 'pictures' of whats going on - I think we can. But they are different from our everyday intuition and pictures we have of the classical everyday world.

    I posted in another thread how I picture QM:
    Here is a way of looking at QM at a foundational level that may make it clearer. Suppose you have a system and some observational apparatus that has n possible outcomes and you associate a number with each of the outcomes. This is represented by a vector of size n with n numbers yi. To bring this out write it as Ʃyi |bi>. Now we have a problem. The |bi> are freely chosen so nature can not depend on them. We need a way to represent it that does not depend on that. The way QM gets around it is to replace the |bi> by |bi><bi| giving Ʃyi |bi><bi|. This is defined as the observable of the observational apparatus. It says to each such apparatus there is a Hermitian operator whose eigenvalues are the possible outcomes of the observation. This is the first axiom of QM. The second axiom says the expected outcome of such an observation is Tr(PR) where R is the observable of the observation and P is a positive operator of unit trace called the state of the system. This can be proven by what is known as Gleason's Theorem if we assume something called non contextuality that you can read up on if you wish. So while the second axiom is not implied by the first it is strongly suggested by it - depending on exactly what you think of non-contextuality.

    The thing is its a picture in a mathematical sense based on a key idea - the outcomes of observations should be expressed in a coordinate free way. I do not think it can be done in terms of everyday pictures.

    Here is another way of picturing it that brings out the essential importance of entanglement:
    http://arxiv.org/abs/0911.0695

    To me its not that we lack pictures - its that they are of a different sort.

    Thanks
    Bill
     
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