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Basic summary

  1. May 12, 2004 #1

    Could someone please post a quick summary of which string theories are out there and how they relate to each other? I could only find partial information on this...

    Thank you.
  2. jcsd
  3. May 17, 2004 #2
    What I have found are the relationships shown http://physics.about.com/gi/dynamic/offsite.htm?site=http%3A%2F%2Fwww.sukidog.com%2Fjpierre%2Fstrings%2F [Broken]. M-Theory is 11 dimensions and converges to different 10-dimensional theories depending on how the 11th dimension is compactified. I've also found info about the 12th dimensional F-theory which converges to M-theory or one of the 10-dimensional theories, depending on how its extra dimensions are compactified. What other theories are there, and how are they related? What about that theroy with 26 dimensions - how does it fit in?
    Last edited by a moderator: May 1, 2017
  4. May 18, 2004 #3
    F-theory?? Where did you find this information? I've been looking and looking everywhere (apparently not everywhere, but a lot of places) for information about F-theory.

    26 DEMENTIONS?? Please, tell me [or us] more about this. Please provide a link as well.

    Anyway, M-theory was originally a set of 5 string theories which seemed different. Edward Witten united them all to form M-theory. quick summary there.
  5. May 18, 2004 #4
    Try search for D Marolf ?

    Edit:removed one F.
    Last edited: May 18, 2004
  6. May 18, 2004 #5
    Google search for "F-Theory" (with the quotes) - the 2nd result is what I was taking my info from. As for the 26 dimensions version, I've heard about it a very long time ago (about the same time I first heard of string theory, iirc). I have no idea how it relates to the others. I've heard recently that it's actually one of those five original theories, but I cannot confirm this, especially given that they are all 10 dimensional as far as I know.
  7. May 18, 2004 #6


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    last time i read they dont even know what is this M theory they only think that all the 5 string theories should be united to one theory, M theory.

    and about F theory it's been developed by camerun vafa (im not sure about his first name) and it adds another time dimension.
  8. May 18, 2004 #7
    Thank you

    Thank you alpha_wolf, and everyone else. :smile:

    Loop Quantum Gravity:
    The 5 original superstring theories where unified by Edward Witten in the 90's. M-theory is the product of the unified theories. What M-theory is, is known but it is not fully understood.

    Two time demensions? So, IOW, two directions in which entropy can expand? Two directions of disorder expanding...that is an interesting idea.
    Say direction A= "future" and direction B= "past".
    the past exists and decreases in disorder. At the same time, "A" will continue to increase "forward" (that is opposite to the direction of "B"). Do I understand this correctly?
    Does this theory allow for time travel to the past? (maybe not ; time travel to the past defies thermodynamics)
    Last edited: May 19, 2004
  9. May 19, 2004 #8
    F-Theory was formulated by Cumrun Vafa (from Harvard),
    looking for an analog theory to M-Theory for describing non-perturbative compactifications of Type IIB theory.

    See for example this


    C. Vafa, "Evidence for F-theory." Nucl. Phys. B 469: 403 (1996).
  10. May 19, 2004 #9
    Can anyone comment on the 26-dimensional version(s) of string theory? Thanks.
  11. May 19, 2004 #10
    The 26 dimensional version of string theory was the original string theory. It predicted only bosonic matter, and also predicted tachyons which was generally took to be a sign that the theory was unstable. It's still used today as a model for playing around with, and serves as an introduction to string theory in quite a few textbooks.
  12. May 19, 2004 #11
    Thanks for your reply. How did it evolve to the 10 dimensional versions?
  13. May 19, 2004 #12
    What is that?
  14. May 19, 2004 #13
    There are five superstring theories. Type IIB is just one of them.

    [type I, type IIA, type IIB, Heterotic E8 X E8, and Heterotic SO(32)]
  15. Jun 10, 2004 #14
    When you add the fermions to string theory by means of supersymmetry, the quantized theory requires 10 dimensions. It is the same origin of the 26 dimensions in bosonic string theory: you quantize and then you end up with a requirement that is related to the symmetry of the massless states (Í don´t know it very well, so I hope someone can explain better this point.)
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