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What's Wrong with QM?

  1. Mar 22, 2005 #1

    reilly

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    After 75 or so years of phenomenal success, some folks have apparently severe problems with Quantum Theory. In fact, this physics forum would not, could not exist without the fruits of QM -- semiconductors and all that.

    Granted, at the margins there are formal issues about measurements. But the plain fact is that we understand measurements well enough to do them and interpret them with substantial success. Many say, and I agree, that QM is the most successful and tested physics theory ever.

    So what's the problem?

    Regards,
    Reilly Atkinson
     
  2. jcsd
  3. Mar 22, 2005 #2

    ZapperZ

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    You missed it by about 25 years, Reilly! :) 1999 was the Centenial year of QM.

    The people that you are complaining about confuse the issue between "interpretation" and "formalism". They seem to think that "Ah, we find so-and-so puzzling and in contradiction to what we believe" as "proof" that QM is wrong. They are confusing "tastes" with valid observation. Often, they do not understand, or have never worked though, the QM formalism in detail.

    As I've said elsewhere, the most convincing evidence of the validity of QM comes from the very devices we use every single day. Condensed matter physics/solid state physics/material science would not be what they are today without QM.

    Zz.
     
  4. Mar 22, 2005 #3

    reilly

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    ZapperZ--We are on the same page. For better or for worse, I started with the development of wave and matrix mechanics, but you are quite correct about more than 100 years for the whole package.

    As I've said, you learn QM by doing it.

    Regards,
    Reilly
     
  5. Mar 22, 2005 #4
    QM has a dirty, empirical history. Using QM to predict results is similar to using Keplers 3 observations to track the motion of the planets. Of course, the tracks have been erased and the logical presentation is now quite slick; but the fact is that QM was guided more in its development by experiment than by actual physics.

    What we really need is someone (It was Newton in the Kepler analogy) to find some real physics that explains why we observe what we do. Instead we have a bunch of Keplers, happy to chart the stars, that have given up finding the cause of their observations,

    Another problem (not with the theory itself) is that it is common for people to talk as if there was "a quantum world" where motion is not continuous, and funny things happen. Then there is the asinine copenhagen interpretation, which says that electrons and such are not even in a particular state untill we observe them! Shrodingers cat paradox disproves the copenhagen interpretation, but many QM zombies continue to tell the Shrodingers cat story not as a paradox, but as a "spooky story about the quantum world". All this stuff bothers me because it is not supported by QM.

    Another irritating point is that people think QM events are ontologically (really) random, which they are not (simply observationally indeterminate like a coin flip). QM has no impact what so ever on the philosophical doctrine of Causal Determinism, but it is often brought up in such a discussion.
     
  6. Mar 22, 2005 #5
    QM is just so confusing, it doesn't make much sense to me.
     
  7. Mar 22, 2005 #6

    ZapperZ

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    And this is BAD?

    What area of physics was NOT guided by experiments? String, superstring, and M-Theory? And we know how "valid" those are, don't we?

    I've just finished listening to a seminar by Harry Lipkin, who himself is a quite well-known theorist. He, of all people, questioned the need for "theorists" in his rather amusing essay "Who Ordered The Theorist" in an issue of Physics Today.[1] The majority of major advancement and new physics have come out of experimental discovery that no theory has predicted. This includes superconductivity, fractional quantum hall effect, and even CP violation. So being "guided" by experiments is not a drawback, but rather a NECESSITY!

    I'm sorry, but Newtonian laws actually "explain" the physics that we observe? Since when? Every time we are able to describe an even lower level of a phenomenon, someone is going to come in and ask "why?". This is not unique to QM only, thankyouverymuch.

    How does the Schrodinger cat disproves CI? Not that I'm that much of a fan of CI, but it "disproves" it? You mean that an electron is not in two simultaneous location in an H2 molecule to produce those bonding-antibonding bonds? Or that the Stony Brook SQUID experiment did not really measure a supercurrent simultaneously going in BOTH directions to produce that energy gap?

    Again, as I've stated earlier, none of these objections have anything to do with experimental evidence. Rather they have everything to do with a matter of tastes and preferences. Nothing has changed or is new here.

    Zz.

    [1] http://www.physicstoday.org/vol-53/iss-7/p15.html
     
  8. Mar 22, 2005 #7

    ZapperZ

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    Then maybe you need to consider the words of one Albert Einstein who said:

    "Common sense is the collection of prejudices acquired by age eighteen."

    Zz.
     
  9. Mar 22, 2005 #8
    Special Relativity is the best example of this. Another good example is Maxwell's addition of the displacement current to Ampere's law; this term is necessary to predict EM waves.


    I believe that nothing is more relevant to this case than the analogy of Kepler, or else maybe Lorentz.

    Keplers laws are based on observation. The lorentz transformations are based on the Michelson Morely experiment. Newton created Universal Gravitation to explain kepler's laws. Einstein created Special Relativity to explain the observed length contraction.

    Is it obvious the distinction that I am trying to draw? Einstein and Newton are the ones who saw through the dark, Kepler and Lorentz just played with puzzle pieces.

    It is obvious why we disagree on this point. Your heroes are the ones who found it first; Kepler, Lorentz, Rydberg. My heroes are the ones who explained what was found: Newton, Einstein, Bohr.

    It seems to me that physics, and history in general, have remembered Newton, Einstein and Bohr much more than Kepler, Lorentz and Rydberg.

    It is not simply a matter of taste, physics is about explaining things.

    Listen to yourself! Of course Newton's laws explain Keplers Observations, don't play naive. It sounds like your attitude is: we can't explain anything so lets not try, physics is only about predicting observables.

    Schrodingers cat disproves the CI because it is absurd to say that the cat is both alive and dead untill it is observed! Because of this contradiction, CI is false. I admit "proof" is too strong of a word, and that your experiments will have to be explained some other way.

    Take comfort in Feynman's quote, which sums up all of the problems with QM:

     
    Last edited: Mar 22, 2005
  10. Mar 22, 2005 #9

    jtbell

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    Is there any experimental evidence for your position, or do you just "know" it to be true?
     
  11. Mar 22, 2005 #10
    If I undertand the original poster, what's wrong with it is that it's difficult for
    people to accept and understand a theory which is so radically at odds with
    everyday experience.

    There's nothing wrong with it as an emperical prediction tool- in fact its quite
    spectacular.
     
  12. Mar 22, 2005 #11
    Your right, I stated my position too strongly. What I mean to say is:

    "Another irritating point is that people think QM events are ontologically (really) random, which there is absolutely no reason to believe. "

    To clarify my position (since I seem to be the antagonist), this is not my problem with QM. My problem is that it is lacking in real explanative power and is likely to be superceded by a physical theory, just as Newton superceded Kepler.
     
    Last edited: Mar 22, 2005
  13. Mar 22, 2005 #12
    To understand: I don't think reilly thinks there's anything wrong with not understanding everything under QM.

    To accept: I aswell find it weird that QM gets such zealous opposition. A theory is to explain and predict, QM has done both and done them well. I don't see a reason for the amount of opposition QM recieves from some people. At times this forum seems to be a place for desperate attempts to disprove QM rather than a way to learn about it.
     
  14. Mar 22, 2005 #13

    dextercioby

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    Untill u give an example of an experiment in the "range" of QM which the latter cannot account for,i disagree.

    And about "likely",how come that in the last 80 yrs,(almost) nothing has changed...?We still have to quantize theories.Which means applying the formalism of QM (either Dirac or Feynman) to all sorts of models culminating with superstrings.


    Daniel.
     
  15. Mar 22, 2005 #14
    Despite recent progress in taming the problems of the pardoxes of wave function collapse, EPR, Schrodinger's cat, etc. in quantum theory, a fundamental question which still remains is the "objectification problem" in that, from the possibilities, why does one event occur and not another?

    We don't know if apparently chance events actually have something behind them. As Murray Gell-Mann says, it's just easier to believe that they are random.
     
  16. Mar 22, 2005 #15

    dextercioby

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    Because,at microscopical level,even for very simple systems,NATURE has chosen to be PROBABILISTIC and simply follow blindly the 6 axioms of Dirac's formulation.
    It's like asking why the speed of the car u're in is 60Kmph and not other value.The answer is that NATURE behaves in such a way that,each time u measure the speed,the # u get is 60Kmph.

    Daniel.

    P.S.WHY WAS THE UNIVERSE (assuming it is only one) CREATED AND BY WHOM??(if u're really interested in phylosophical questions).
     
  17. Mar 22, 2005 #16
    Maybe you are not speaking english very well, but this statement is ludicrous! Imagine the young Newton being taught:

    "Because when it comes to the planets, NATURE has chosen to be ELLIPTICAL and simply follow blindly the 3 axioms of Keplers formulation."

    Rubbish! Quantum theory itself is acceptable, but the terrible thing is that many professional physicists see no need to progress beyond it!
     
  18. Mar 22, 2005 #17

    dextercioby

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    We have no theory in which Dirac's axioms are theorems.If we did,it's just the same theory,but in von Neumann's formulation or Feynman's...

    So,i'm looking forward till the day QM's axioms would become theorems/consequences of other axioms...

    I may not live that day.Maybe your grand-grand-grandnephews would tell mine that their grand-grand-granddaddy was wrong 200 yrs before.

    Daniel.
     
  19. Mar 22, 2005 #18

    reilly

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    There's one thing I've never understood about the Schrodinger cat problem. It has nothing to do with QM, and everything to do with standard probability matters. A horse in a horse race certainly is not simultaneously winning and losing. When my kids were born, we did not know the sex of the kid until actual birth. It is absurd to say that throughout the gestation period the child was both male and female. The point is in anything that is described by probability -- or not-- that you don't know until you look. Indeed anybody can claim the cat is simultaneously dead and alive, but why do so? To the best of my knowledge, no one has ever seen a dead/alive cat. It seems to me that the justly famous Occam would say: it's either dead or alive, as we know cats to be, and when we look we'll find out what its state is. Any other view just complicates the matter.

    Copenhagen? What that means to most of us is that the absolute square of a normalized wave function is a probability density, as Born suggested. As far as I can figure out, classical probability is as subject to collapse as QM. That is, measurement simply tells us at that moment what is, whether an electron in a scattering experiment, or the price of IBM stock, a sales forecast, or what you will have for dinner in two weeks.

    If you work with QM, you develop physical intuition about how it works, you learn that it is good physics with immense explanatory power. Use scattering theory, the Lippman-Schwinger Eq., compute the coherent field that a classical electric current produces, compute nuclear decay rates. For a particularly intuitive physical approach to QM, study all the work behind the theory of chemical bonding -- Linus Pauling's book on bonding is absolutely brilliant, and there are many physically based arguments about the QM involved. Work through the BCS theory of supercoductivity, Cooper pairs, etc, etc. etc. I suspect that many who seem offended by the precepts of QM have not worked with it much. The claim that QM has no explanatory power is absurd.

    Further, why do any of Newton's Laws work? People during the Greco-Roman times or during the Dark Ages would have felt Newton's work was preposterous; they had an enormously different world view. If QM is strictly empirical, simply a tool to compute, then the same must be said about Newtonian mechanics. In the final analysis why are Newton's Laws, in practice, different than the Schrodinger Eq. After all our acceptance and comfort with Newton comes simply from years of experience -- Aristotle, brilliant as he was, would have had an equally difficult time making any sense of Newton or Schrodinger.

    So it goes. But I'll say again: you learn QM by doing it.

    Regards,
    Reilly Atkinson
     
  20. Mar 22, 2005 #19

    ZapperZ

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    I'm sorry, but SR is NOT guided by experimental observation? Einstein was very troubled (as were the rest of the physics community) with the non-covariant form of Maxwell Equation under galilean transformation. This is simply contradictory to ALL experimental observations. And Maxwell Equations themselves came out of experimental phenomenology. Coulomb's law was certainly NOT derived out of First Principles, and neither did the rest. They are certainly very strongly guided by experiments.

    Newton didn't "explain" anything. Newtonian laws are phenomenology. They connect seemingly unconnected phenomena, but it still doesn't explain why things are "attracted" or the nature of forces. It is simply one "level" down from Kepler. I could say the same about QM, where it "explains" HOW certain things work that classical mechanics could not. However, I won't, because if one were to examine it closely, all we have in physics are just descriptions.

    My heroes? You mean I don't get to choose my heroes, but rather get assigned to them by you?

    My "hero", if there ever is one, is John Bardeen.

    Look carefully. Newton Laws only goes one level deeper than Keplers. It still "explained" nothing! Newton laws left large holes in terms of explanation. It still only describes things. There is a huge difference between "explanation" and "accurate description". Just because you can come up with a theoretical model to describe a set of observation, doesn't mean you have explained it.

    It is absurb because you are trying to force a square object through a round hole, and then blaming the hole for not fitting with your square object. If SR has taught us anything, it is that our cherised prejudices may not fit when we go beyond the boundary of classical physics. Why can't the same thing happen at the QM scale? Why would "position", "momentum", "energy" etc the way we defined it classically make any sense at the QM scale? It seems that we are forcing nature to accept those concepts, and then when she spits out things that simply don't gell with our classical concept, we blame her instead of the fact that those concepts simply do not fit!

    Superposition principle is alive and well (simultaneously). Chemists have seen these effects WAY before QM was formulated, and have been unable to figure out a rational description for them. Material scientists make use of various bonding-antibonding bands in looking at band structure of materials all the time (example: the split bands in dual-layer Bi2212 high Tc superconductors). You simply cannot brush this aside and hope to explain this "some other way". There has been no "other way".

    Again, physics has never been challenged by "preferences" or tastes. Every single challenge to expanding it into new areas have always been done by valid experimental observations. There have been none, no experimental observations that so far have contradicted QM. I would LOVE to find one! As an experimentalist, I love nothing better than to find something that squish a theory or idea.

    Again, what you have brought up is nothing new. Search PF if you don't believe me. We periodically get this all the time on here where someone either question the validity of QM, or not happy with what it does (or doesn't do). So far, all of them have accomplished nothing but tired fingers.

    Zz
     
  21. Mar 22, 2005 #20
    Thank you for admitting this, it is my main point. We would all like to see a theory which supercedes quantum mechanics. Except for ZapperZ, who would like to discourage any progress in physics:

    If at first you don't succeed, try try again. Because giving up is not winning.
     
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