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

Has string theory solved all problems?

  1. Apr 24, 2008 #1
    I know string theory is not proved yet.Now Biggest hope is LHC. But theoretically has string theory solved all problems or still there are unsolved problems in physics and what are those?
  2. jcsd
  3. Apr 24, 2008 #2
    There are lots of problems remaining, but string theory seems to have solved many.
    To my knowledge, the problem is, not even the LHC will really be able to test string theory (there is a chance it will reveal something, but not likely) - thats the problem. String theory hasn't made any predictions that are at all testable -> which really weakens it.
    The question is generally whether a particle collider would have to be the size of the solar system to test string theory, or the size of the galaxy... so future testing isn't especially feasible either.
  4. Apr 24, 2008 #3
    Which ones and how so?

    EDIT: Unification of interactions comes to my mind (not sure to what extent strings really do). Any others?
    Last edited: Apr 24, 2008
  5. Apr 24, 2008 #4
    If it has, it's news to me :)

    Hopefully it hasn't, otherwise I wouldn't have a job.
  6. Apr 24, 2008 #5
    Well, string theory does imply gravity.
  7. Apr 24, 2008 #6
    The main one, of course, is unifying all of the fundamental forces of nature.
    Additionally, string theory seems to explain why/how things have mass and what that means (how they do this, i have no idea!).
    It also "explains" why there are 3 groups of fundamental particles... supposedly.
  8. Apr 25, 2008 #7
    Sure, in principle if confirmed...
    Mass is in the vibration mode of the string.
    We have not much clue of how it is supposed to do that. Another way to say it : once you have chosen (say) the right Calabi-Yau, you get the right SM (can provide reference) but you still need to explain why you chose this Calabi-Yau.
  9. Apr 25, 2008 #8

    George Jones

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The right SM including electroweak symmetry breaking? Zwiebach's book says that electroweak symmetry has yet to worked out in detail, but this might be out of date.
  10. Apr 25, 2008 #9


    User Avatar
    Gold Member

    Mass of the excited nodes is the vibration mode of the string. But the observed elementary particles come, according to the string lore, from the massless sector. They get their mass from the Higgs. So string theory agrees with the common lore but does not innovate upon it.

    String theory has new sources of mass: the excited modes on one side, the size of the compact dimensions on another. But they are not used in the standard model building; both of them are tied to Planck scale.

    As for the 3 generations, I would like to as lzkelley about where did he get such suggestion. Nobody in the standard bussiness claims to explain the number of generations.
  11. Apr 25, 2008 #10
    string theory is not a falsifaiable theory and this is the problem !!
  12. Apr 25, 2008 #11
    Yes, I think that still holds. But still, once you have chosen the right stacking of D-branes, you can get results remarkably similar to the (SS) standard model structure.
    Local models of Gauge Mediated Supersymmetry Breaking in String Theory
    The Standard Model in String Theory from D-branes

    OK, how about that :
    TeV Strings and Collider Probes of Large Extra Dimensions
    Here you go, you have standard-model predictions, string theory predictions, they clearly differ and only await for more precise measurements to be distinguished, available measurements with their error bars being explicitely shown, error bars being clearly reduceable in principle. And before you claim this paper is crackpot theory, please pay attention to the authors, and the fact that it has been published in a respectable peer-reviewed paper (Phys.Rev. D62 (2000) 055012).

    It is fascinating that, I myself not being a huge fan of string theory, can get tired of people constantly reporting that string theory is wrong, string theory is not even a theory, string theory is science-fiction...
  13. Apr 25, 2008 #12


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Very interesting article. It's not quite a full fledged string theory calculation in the sense that a certain ad hoc background of branes must be assumed. So in that respect it's in part like brane world scenario (eg Randall-Sundrum) who assume a certain brane configuration to start with. Still, it's very interesting to see explicit string calcualtions of processes carried out and related to observed processes.

    I agree. The backlash went too far and became irrational at some point. I would agree with statements to the effect that string theory is not a complete theory yet and that there is much work left to do before it can be tested. So in that sense, the present state of string theory cannot be considered a satisfying attempt at a theory of everything; too much is still missing. But it makes no sense to say that string theory is dead, that it there is no hope to ever test it, etc etc. This type of statement is completely misguided and narrow-minded, imho.

    I am the first to grant that in its present form, string theory is not a complete theory and it can't be "killed" so much work remains to be done. However, the achievements of the theory are impressive.

    Some achievements are purely conceptual. As far as I know, string theory is the only theory that fixes the number of spacetime dimensions. Other approaches (say, LQG) must take that number as an input and can't justify it.

    String theory requires the existence of gravity at the same time as the other forces of nature. In other approaches (say LQG) gravity must be postulated from the start.

    Supersymmetry is without any doubt a beautiful concept. It's the only way to mix an internal symmetry with spacetime symmetries and at the same time it connects bosons and fermions. In addition, gauging susy produces GR (which is then called supergravity). Supersymmetry may only be an idea which is not a symmetry of Nature, but it's one of those beautiful ideas that feels like it must have been used by Nature. In any case, superstring theory automatically leads to supersymmetry! In other approaches (like supergravity), supersymmetry must be put in by hand at the very start.

    To summarize, in string theory (by which I mean superstring theory obviously) internal consistency alone fixes the number of spacetime dimensions, the existence of gravity and supersymmetry (as well as fixing the possible gauge groups). It's hard not to be impressed.

    And even if string theory would turn out not to be valid (or if it turns out that we can't never reach a more mature form of the theory allowing it to be falsifiable) it has already lead to important advances in maths and as a computational tool for point particle field theory. So it has already been useful notwithstanding whether it wil be successful as a TOE or not.
  14. Apr 25, 2008 #13
    I don't know if string theory has solved all problems...

    I was undecided about whether to wear my brown pants or black pants today. I turned to the landscape of string theories, but they were completely unhelpful.
  15. Apr 25, 2008 #14
    That's not correct. The experimentalists just need to get off their asses and build more powerful colliders =)
  16. Apr 25, 2008 #15


    User Avatar
    Gold Member

    My understanding is that string theory resolves the disconnect between GR and QM - two of the most important constructs of 20th century physics.
  17. Apr 26, 2008 #16


    User Avatar
    Science Advisor
    Gold Member

    It is difficult to falsify string theory without wreaking havoc upon mathematics. But, inability to falsify does not confer credibility. It is also difficult to falsify the 'god' hypothesis. This, IMO, raises a fascinating question: does ST allow for the existence of 'god'? I think so. As much as I distrust ST [not because I think it is wrong, just too poorly defined], I will never agree to any theory that forbids a 'god' [first principles].
  18. Apr 26, 2008 #17
    Every green question deserves a green answer.
  19. Apr 26, 2008 #18
    String Theory may be a never_ending story in modular or periodic dynamic space?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook