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Quantum theory vs String theory (Who's the best?)

  1. Oct 11, 2012 #1
    Just about few hours ago,my friend and i argued about which theory is the best theory nowadays ever existed. I claim that string theory is the only game in town as what i heard from Dr. Michio Kaku's TV shows, while my friend strongly disagree with it. He claimed that quantum theory is the best theory which agrees with experimental results whereas string theory is just a theory without any evidence.

    Is that true about what my friend just said?

    Are there any experimental proves for the sting theory (or even m-theory) till today?

    Which theory describes the entire universe better? Quantum o String?
     
  2. jcsd
  3. Oct 11, 2012 #2

    Nabeshin

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    The term 'string theory' itself refers to the quantum theory of strings. The distinction, as you and your friend seem to have understood it, does not exist.
     
  4. Oct 11, 2012 #3

    marcus

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    Are there any experimental proofs for string theory? No.
    The theoretical framework has not given us any clear firm predictions of new phenomena by which it could be tested. The theory sort of predicts that there would have been supersymmetry seen at LHC levels of energy---some string theorists expressed confidence SUSY would be seen, but it wasn't. There was also some expectation of observing evidence of extra dimensions, but that did not materialize either.

    By contrast Quantum Mechanics (QM) is an enormously successful physical theory, perhaps the most successful in human history. It has made thousands of predictions concerning hundreds of different sorts of phenomena and has always been right.
    The beginnings of QM go back to around 1926 and earlier. It is now an old well-established theory that has passed a lot of tests and has a lot of success to its credit.

    The trend has been to build out from QM and make quantum theory apply to more and more things, get into more areas of nature, at higher energies, to more different kinds of particles, at smaller scales and so on.

    There is no competition between QM and String. String is a comparatively recent research program which might eventually succeed (as some hope) or might fail (as some think it already has).

    Neither QM nor String gives a complete description of Nature. There is no contest between them. The String research program does not aim to rival QM or to replace QM. If it were to be successful it would simply be an extension of QM. If someday the String program comes out with a single clear unique theory it will actually be a QUANTUM THEORY OF STRINGS.

    And if String fails there will probably be some other extension of QM that succeeds. Quantum Theory looks like it is here to stay. That gives you my perspective on it, which is about the only way I can respond to your question.

    There is really no comparison between the two things. they are vastly different sorts of theory.

    If your friend likes QM and wants to learn more about it, encourage him. It may stand him in good stead in his further education. QM will still be around when people have forgotten all the hype and hot air of today's TV science.
     
    Last edited: Oct 11, 2012
  5. Oct 12, 2012 #4

    Nabeshin

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    By this do you simply mean all physical theories should be thought of as effective theories, or simply as models for physical reality?
     
  6. Oct 12, 2012 #5
    Does it mean that string theory is a subset of quantum theory?
    Anyway what is the major difference between quantum n string??
    :confused:
     
  7. Oct 12, 2012 #6

    atyy

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    String theory is a subset of quantum theory. There are quantum theories of particles, fields and strings. At low energy, quantum string theory is approximately a quantum theory of fields, which at low energies is approximately a quantum theory of particles.

    We know that our world is well-described by a quantum theory of fields. Although string theory at low energy produces a quantum theory of fields, we don't know if the fields match those in our world.
     
  8. Oct 12, 2012 #7

    Demystifier

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    I like the idea that particles are just a low energy approximation of strings, while fields are only an auxiliary mathematical tool that is not really necessary in particle physics. To see how to get effects of QFT directly from quantum particles and without quantum fields see e.g.
    A. O. Barut, I. H. Duru, Phys. Rep. 172, 1 (1989)
    http://arxiv.org/abs/hep-th/0311180
    C. Schubert, Phys. Rep. 355, 73 (2001)
     
    Last edited: Oct 12, 2012
  9. Oct 12, 2012 #8

    atyy

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    OK, how about if I said "fields"=particles with particle creation, while "particles"=particles without particle creation?
     
  10. Oct 13, 2012 #9

    tom.stoer

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    Quantum theory means a class of tools like 'quantization', Hilbert spaces, state vectors and wave functions or functionals, operators and observables, path integrals, propagators, S-matrix, ... which can be applied to various models of nature. So the specific applications are non-rel. quantum mechanics, quantum field theory (including gauge theories, standard model, ...) and (quantization of) string theory - and other theories like loop quantum gravity.

    It's like asking for the difference between 'mechanical engineering' and a 'hammer drill'.

    Therefore you may ask for the difference between quantum field theory and string theory; that's a reasonable questions.
     
  11. Oct 15, 2012 #10

    Demystifier

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    It would be fine.
     
  12. Oct 15, 2012 #11

    haushofer

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    Why? String theory is from a lot of perspectives a two-dimensional QFT.
     
  13. Oct 15, 2012 #12

    tom.stoer

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    In post #1 the question was about the difference between quantum theory and string theory. That does not make sense. String theory is an application of quantum theory (like quantum mechanics and quantum field theory). That's what I wanted to make clear.

    So I wanted to stress this difference whereas you want to stress the common features.

    My question to you is this: is string theory a two-dim. QFT only from a lot of perspectives? or is (every) string theory identical (equivalent, dual, ...) a two-dim. QFT?
     
    Last edited: Oct 15, 2012
  14. Oct 15, 2012 #13

    haushofer

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    I admit I was a bit vague on that :P I think that every string theory (whatever kind of fluxes, Calabi-Yau compactification, etc.) should be derivable from the world-sheet point of view, and hence should be a two-dim. QFT. But this is very hard to proof. I believe, but I'm not an expert, that this is one reason why e.g. it is not clear if certain flux compactifications make sense at all.
     
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