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I Is string theory dead or still valid

  1. Apr 18, 2016 #21


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    I'm not sure what you mean with "Einstein's theories". GR? In that case I don't agree; that theory only contains one parameter kappa, which is fixed by the correspondence principle.
  2. Apr 18, 2016 #22
    oh I understand. You mean because of the 10 ^500 universes as parameters. Parameters are different to these 10 ^500 universes. If we would want a SUSY for QM then we would have over 200 constants as parameters and not less than 50. In stringtheory we have only very few, if any at least. I was talking about predictions. It was impossible and unimaginable to detect, that the clock 20 meters above is running faster than the clock on the ground. For the physicists in this time highly speculative
  3. Apr 18, 2016 #23
    but not impossible to detect that something strange and inexplicable with current theories was happening to the orbit of Mercury.
    GR successfully explained this.
  4. Apr 18, 2016 #24
    Moduli stabilization remains an active issue.
    When scanning for dS vacua in string theory one problem is that we don't keep any SUSY complicating the result.
    Another is that often there are quantum corrections which we cannot calculate.

    Also the 10^500 is an old, very crude number based on Calabi-Yau, flux compactifications. This is a small subset of solutions which cannot be de Sitter as a matter of fact since CY three-folds are ricci flat. (Ricci curvature scalar of internal manifold should be negative)
    More on the landscape

    haushofer's first reply was a bit tongue-in-cheek by the way (if I'm not mistaken)
  5. Apr 18, 2016 #25
    we can have different opinions on that. Witten is not of fan of landscape topologies. It is an open field, we need to examine more detailed. But that we have the possibilities to think in that ways is alltogether stringtheory, we wouldn't have in QM. This is showing the powerfull framework we have now
  6. Apr 18, 2016 #26
    I agree, I'm working with group manifolds and the coolest thing happened, I reduced the possible manifolds that might allow dS vacua to 4 (compactification to D=6, trying to find a toy model).
    It turns out I get almost exactly the same equations (unsolved for now) for each manifold. This suggests something deeper could be happening but I haven't seen it yet. (my advisor and his collaborators has a hunch but its far from conclusive)

    That's the deal with string theory and supergravity, often we have a feeling and need to investigate more but going deeper takes time (which I no longer have).

    I'd say the answer to the OP is that it's not dead but there are some issues we don't fully understand.

    And my opinion wrt other candidates for a theory of quantum gravity is that we need some authorities that know two of the theories very well.
    Who knows one could use ideas from other theories in whatever flavour they like best.
  7. Apr 18, 2016 #27
    Similar to my opinion. We need a 3rd and fourth revolution. I guess also, we will get these inspirations from complete different fields to string theory. We will see.
  8. Apr 16, 2018 at 5:28 AM #28


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    Then you surely must have seen this one,


    To me, it becomes a bit suspicious how every time something initially bad for string theory turns out to be good. Just sayin'.
  9. Apr 16, 2018 at 8:04 AM #29
    Is it true non-perturbative string theory or M-theory cannot be reduced to QFT except in some limits? Why?

    What are the most complicated forces/new fields of nature that QFT can be valid and where it is not (then M-theory or something more complicated takes over)? Any reference of the limitations of our vintage QFT?
  10. Apr 16, 2018 at 8:53 AM #30


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    Can you name any testable predictions made by M-theory and tell us how the results compare to observations? I would not consider it "valid" until it is an actual theory where one can do calculations and compare the results to observations. I do not think that this is yet the case.
  11. Apr 17, 2018 at 7:49 AM #31


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    I think this is another manifestation of "duality". There is no such thing as, good or bad, it is all just a matter of choice of background context ;-)

  12. Apr 17, 2018 at 8:26 AM #32


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    It seems to me that the name "string theory" is a misnomer. A theory in physics is a model where I can do calculations and compare the results of these calculations withe experiment. SInce this isn't (yet) the case in string theory, I think it would be more appropriate to call it the "string concept" or the "string idea".
  13. Apr 17, 2018 at 10:44 AM #33


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    ... or "string thing"?
  14. Apr 18, 2018 at 10:51 AM #34


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    Well, string theory is a 2-dimensional (superconformal) quantum field theory. But quantum field theory in itself is a paradigm, not a theory. So I guess that's where the bad naming starts.

    Regarding experiments: I think people doing AdS/CFT would disagree. String dualities are testable.
  15. Apr 18, 2018 at 12:27 PM #35


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    Quantum Field Theory can do detailed calculations that can be compared to experiment in exquisite detail. Things like scattering amplitudes and the electron or muon magnetic moment. It's not at all like string theory in that respect.

    Can you name a "string duality" that has been tested against observations?
  16. Apr 18, 2018 at 6:54 PM #36


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    String theory has never been established to be a valid description of the real world. But, it isn't dead. A plurality of theoretical physicists in the world are still working on it.
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