Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Is string theory dead or still valid

  1. Apr 18, 2016 #21

    haushofer

    User Avatar
    Science Advisor

    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 #28

    haushofer

    User Avatar
    Science Advisor

    Then you surely must have seen this one,

    https://arxiv.org/abs/1804.01120

    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 #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 #30

    phyzguy

    User Avatar
    Science Advisor

    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 #31

    Fra

    User Avatar

    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 ;-)

    /Fredrik
     
  12. Apr 17, 2018 #32

    phyzguy

    User Avatar
    Science Advisor

    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 #33

    PeroK

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    ... or "string thing"?
     
  14. Apr 18, 2018 #34

    haushofer

    User Avatar
    Science Advisor

    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 #35

    phyzguy

    User Avatar
    Science Advisor

    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 #36

    ohwilleke

    User Avatar
    Gold Member

    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.
     
  17. May 26, 2018 #37
    Well as Niels Bohr might say, ST —or any other theory for that matter— cannot describe the actual, real, underlying world of particle physics, it can only say something about it.

    In that sense ST has said a lot, a whole whole lot over 40+ years now. Maybe too much for some people’s taste.

    The day all that can be tied to a feasible experimental set-up, ST will explode. I would think cosmology is a better candidate to provide that experimental link one day than HEP/particle physics...maybe with the Webb space telescope and some high-resolution soundings of black holes?...


    IH
     
  18. May 27, 2018 #38
    The question, "Is string theory dead or still valid?" highlights a common failure of science education that instills (or allows) folks to frame scientific questions as false dichotomies when it comes to the validity of theories.

    It is more complicated than "dead or still valid."

    Scientific theories are never really proven, but given a long enough track record of making testable predictions that are later confirmed, one can say a theory is well supported and validated. String theory never came anywhere near this.

    Scientific theories can also be disproven by experimental results that contradict their predictions. String theory has not really suffered this fate either, since there have not been many (or any) real predictions within the abilities of modern experiments to test them.

    The ups and downs of string theory have been more like a scientific popularity contest falling in and out of favor (and funding) rather than really meeting the fundamental scientific tests of validity or testability.

    https://blogs.scientificamerican.com/cross-check/why-string-theory-is-still-not-even-wrong/
     
  19. May 27, 2018 #39

    FactChecker

    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    I have always thought that a statement like this deserved some discussion. Clearly the theory agrees with many facts that were already known. The difference between those earlier-known facts and later-confirmed predictions is just the timing of the development of the theory. Of course, one must be sceptical of theories that were rigged to agree with already known facts, but I think there should be better criteria applied than the simple timing of the development of a theory. Some theories fit very simply into earlier accepted theories while others seem like "Rube Goldberg" contraptions.
     
    Last edited: May 27, 2018
  20. May 27, 2018 #40

    MathematicalPhysicist

    User Avatar
    Gold Member

    It's undead.
    A zombie!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted