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Shortcomings of quantum theory

  1. Sep 5, 2010 #1
    What do members think of the idea that the philosophy which began quantum theory in the first place was inadequate to explain and describe reality in a sufficiently deep way, so that we now have a theory which in many ways fails to describe the reality which we experience in the world?
     
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  3. Sep 5, 2010 #2

    tom.stoer

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    There was no philosophy of quantum mechanics which misguided physicists. There were some classical concepts (and related philosophical reasoning) which were unable to explain the quantum world. So instead of keeping inadequate classical concepts quantum theory had been invented.

    QT has been proven to be the correct decription of nature, in the sense that its predictions agree with experimental results (or al la Popper: no experimental falsification of QT predictions has been observed).

    At a later stage one tried to establish philosophical reasing, adjusting certain philosophical concepts etc.

    So it is NOT the case that QT fails to describe reality! It's the other way round: our classical concepts regarding "reality" DO NOT FIT to the quantum world. It's nature that tells us that our classical philosophical concepts failed!
     
  4. Sep 5, 2010 #3
    And which philosophy was ever adequate?
     
  5. Sep 5, 2010 #4

    tom.stoer

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    Any interpretation of QM is adequate in the sense that it respects proven facts. But that does not mean that these interpretations are adequate in a philosophical sense. Personally I accept QM as a theory describing nature, but don't LIKE any interpretation I have seen so far.
     
  6. Sep 5, 2010 #5
    Who cares about "philosophical sense". And what it is anyway? There are as many "philosophical senses" as there are philosophers, and probably many more.
    Instead of talking generalities ask a particular question and perhaps someone who knows the subject will answer your question.
     
  7. Sep 5, 2010 #6

    tom.stoer

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    Did you aks me? or woolyhead?

    Anyway, you seem to believe in the shut-up-and-calculate philosophy. But even this IS a philosophy, so there's no escape.

    OK, here's my question: does the moon exist even if nobody is looking at it?
     
  8. Sep 5, 2010 #7
    "does the moon exist even if nobody is looking at it?"

    What it has to do with the title of this thread which is not astronomy but quantum theory? Ask astronomers and they will laugh at you.
     
  9. Sep 5, 2010 #8

    tom.stoer

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    The question is just a warm up for the next one: does an electron exist even if there's no measurement observing it?

    It is just to exemplify that there are questions which may seem to be ridiculous in a physical (positivistic) context but which deserve philosophical reasoning. Remember: the first question in this thread was about quantum mechanics and philosophy.
     
  10. Sep 5, 2010 #9

    DevilsAvocado

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    Welcome to PF woolyhead!

    I understand what you mean, but I think that the "shortcomings" you are talking about, depends on what you set out to achieve from the beginning. This was the scientific goal for Niels Bohr:
    "It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature."

    "Our task is not to penetrate into the essence of things, the meaning of which we don’t know anyway, but rather to develop concepts which allow us to talk in a productive way about phenomena in nature."

    "There is no quantum world. There is only an abstract quantum physical description."

    Now, to me it seems a little 'peculiar' if we happened to live in that century which had fastest technological revolution (so far), and besides that – found the final answers of everything.

    I don’t make sense...

    And we know it don’t make sense since Einstein’s General Relativity is not 100% compatible to Quantum Mechanics. One or both must be slightly 'incomplete'. That’s a fact.

    This by no means indicates that QM is wrong. In fact, QM is the most precise theory we got. But to make a parallel; before Einstein’s relativity, Newton’s law on gravity was the only one, and it worked (almost) perfectly... and then Einstein came up with his theory, that is 100% backward compatible to Newton gravity, but makes new predictions about 'extreme' situations.

    My guess is that we will see something similar in the future, in a new theory that will merge QM & GR, and be 100% "backward compatible".
     
  11. Sep 5, 2010 #10

    tom.stoer

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    I think the question was not about physical shortcomings of QM (there aren't any, except perhaps for quantum gravity) but a clash of quantum mechanics and "reality which we experience".
     
  12. Sep 5, 2010 #11
    Exists? Please, define "exists" in this particular context.
     
  13. Sep 5, 2010 #12

    tom.stoer

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    "Exist" in just the same way as the moon exists even if nobody is looking at it.
     
  14. Sep 5, 2010 #13
    This is not the same context. Electron can not exist in "the same sense" as Moon exists. But why do you have doubts about existence of electrons? They have mass, they have charge, they have spin, they are just tiny-ting and hard to observe the same way as you observe the Moon. And when you say "nobody is looking", you mean "human being"? Will a cat count? Or a frog?
     
  15. Sep 5, 2010 #14

    tom.stoer

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    I just want to clarify that there are philosophically reasonable questions outside the physical world.

    You say that the context for the moon and for the electron is different - why? Both are physical objects, both have mass, charge, angular momentum etc. Both can be described by quantum mechanics in principle (even so for teh moon it's rather complicated).

    The problem is that "existence" cannot be defined within physics. If you define "existence" in a positivistic sense (according to phenomenology) than you cannot explain why "objects" can exist even if nobody is looking at them. If you define existence in an ontological sense then you must explain what existence means beyond phenomenology.

    In quantum mechanics you cannot define the "existence of an electron". All you have are state vectors and operators. But an electron IS neither an operator nor a state vector. It can be DESCRIBED by a state vector but it certainly IS not a state vector. So the question is what this IS means.

    This has been discussed by Einstein, Bohr, Heisenberg, Schrödinger, Bohm, Wigner, Popper to mention just a few. They all agreed on the mathematical foundations of quantum mechanics, how to apply them in order to make physical predictions. But they did not agree on "existence", "IS", "realism" etc.

    I do not doubt that the electron exists, but I insist on the fact that neither you nor me can explain what it MEANS that the electron EXISTS. That's beyond physics.
     
  16. Sep 5, 2010 #15
    Well, that depends on which quantum mechanics. There are variants. Does space and time exist in quantum mechanics? They are not state vectors and operators. Yet few people doubt that they exist. On the other hand in Bohm's version electron exists and moves along a nonclassical trajectory. Which particular version will give a better agreement with observations is yet to be seen. Different formalisms are still under development.
     
  17. Sep 5, 2010 #16


    The question is that NOBODY(esp. you) knows the answer to the question how qm relates to the world outside. You can keep asking and advising others to ask, but this can only serve to kill time and so that it passes by.
     
    Last edited: Sep 5, 2010
  18. Sep 5, 2010 #17
    These 'variants' are just pure hypothesises and idle speculation. Do you understand that there is a difference between "knowledge" and "speculation"?



    You have a LOT more to learn before ou can make such sweeping generalizations, as to who doubts what.



    It's still a classical-like trajectory.What's your point?



    I think you need to tone down your statements towards Tom(an actual physicist), as he's way more knowledgeable than you. The different formalism that you seem to imply has trouble with relativity and places ALL the mystery of qm into the pilot wave, thus 'removing' the other mysteries. If you are advocating this approach, be warned that it's not considered quite mainstream science here by the mentors.





    Astronomers are the last group of physicists who'd be qualified to take on this question.





    So what that electrons have charge, mass and spin AT measurements? What is that supposed to tell us about unmeasured, superpositional electrons? Does it make sense to think that you are the first person to propose common-sense lay reasoning to iron out the paradoxes of the quantum world?
     
    Last edited: Sep 5, 2010
  19. Sep 5, 2010 #18
    Quantum mechanics is a theory formulated by human beings in order to describe the world outside. So it relates by its very construction.
     
  20. Sep 5, 2010 #19

    The question is:

    What does its construction say about the world of cars and Moons(on top of giving us predictions about measurements)?


    If you don't have means to prove empirically what you want to propose as the True interpretation(which of course you don't), leave the others(esp the more knowledgeable) to ponder what it all means for the world outside. There are some of us that love to hear their considerations.
     
  21. Sep 5, 2010 #20
    Mainstream science? What is your definition of this term? Don't you know that the standard qm has also troubles with relativity?
     
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