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What's wrong with CM? and QM?

  1. Nov 10, 2005 #1
    Hi,
    There is one question that couldn't answer when studying physics (or found in any text): Where originally did Classical Mechanics went wrong?
    QM texts just go straight into the details and nuts and bolts of QM without touching this question, and
    general physics texts do talk about phenomena such as interference, light particle/wave duality, etc... without actually stating a phenomenon showing the discrepancies between calculations done by CM, QM and empirical data.
    It could be that I haven't read all the books carefully enough :frown: or haven't read the right sort of thing... so if anyone can clarify this for me that would be incredible. :!!)
    And similarly, what is the problem between QM/Rel and putting the two together?
    Thanks!
     
  2. jcsd
  3. Nov 10, 2005 #2

    ZapperZ

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    Then you must have come across only awful texts. Most modern physics text that I have dealt with will start off with showing you the blackbody radiation problem and the ultraviolate catastrophe. These two are historically the dominant problem that classical mechanics could not solve until Planck's work.

    Zz.
     
  4. Nov 10, 2005 #3
    If there's nothing wrong with it, then maybe you could suggest a scheme for putting the two together?
     
  5. Nov 11, 2005 #4

    jtbell

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    Also the photoelectric effect and the whole question of the structure of the atom, which were puzzles before Einstein and Bohr applied Planck's work to them. Much of the development of quantum mechanics was motivated by trying to explain the emission spectrum of hydrogen and other elements.
     
  6. Nov 11, 2005 #5
    That is actually a very good question. The classical NO GO arguments in standard textbooks quantum physicsts love to embrace are way too simple and naive. Now, there is one way to distiguish QM from *BELL local* realist theories and that is by doing EPR experiments; these are so far inconclusive since the experimental setups are not refined enough yet to create the ideal theoretical situation. To make the quantum lobby happy here: QM is still superior over local realist theories so far but (a) has its own problems (the eighty years old untamed cat) which will require a fundamental modification of QM (b) this superiority is mainly due to a stream of positivistic madness in the years 1920 which made every further investigation into classical theories almost impossible (albeit very smart people in that time certainly found that worthwhile). Now, I hold it entirely possible that local realism in the end is not sufficient and that there is some non locality in nature, but this (a) is not by any means a fact and (b) does not imply at all that a deepening of our understanding of CM one the microscale is a worthless persuit (on the contrary).
     
  7. Nov 11, 2005 #6

    ZapperZ

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    Before you decide to open another can of worm and possibly hijack this thread into another different avenue that has already been covered in SEVERAL threads in this forum, REREAD the original post, especially the passage that goes

    [my bold]

    I interpret this (and so did everyone else responding to this thread except you) that the OP is asking for the HISTORICAL impetus in the introduction of quantum physics.

    I am very certain that DrChinese and everyone else would be more than happy to entertain you on the issue that you wish to discuss in the already-existing threads.

    Zz.
     
  8. Nov 11, 2005 #7

    ahrkron

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    As others have already pointed out, without the quantum hypothesis, Thermodynamics makes predictions for the radiation of a "balck body" that are clearly wrong. Once you adopt the idea of quanta, the difficulty disappears and the radiation can be described very precisely.

    Also, without the quantum hypothesis, atoms are expected to disintegrate quite fast, and the photoelectric effect is hard to explain.
     
  9. Nov 11, 2005 #8
     
    Last edited: Nov 11, 2005
  10. Nov 11, 2005 #9

    DrChinese

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    I am still waiting (licking my chops more like it) for Careful to start a thread on the subject which he/she so obviously wants to discuss...
     
  11. Nov 17, 2005 #10

    vanesch

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    Ok, before this makes everybody nervous, let us start a new thread on this, and keep this one for the standard argumentation of why it was needed to switch to QM from the Maxwell+classical particle point of view.

    I'll start it... with the title "revival of CM ?" if that's ok with you guys , and move the posts by reilly and Careful there; refrain from having this discussion in this thread.

    https://www.physicsforums.com/showthread.php?p=828375#post828375
     
    Last edited: Nov 17, 2005
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