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Does Penrose theorem about Space-time forbid 'Strings'

  1. Aug 2, 2007 #1
    Penrose proved that a more than 4-dimensional spacetime would be unstable.. does this mean that String theory is completely wrong?? (since this only works on 11 dimensions).

    Also without offending nobody's beliefs .. .what're the proofs for the existance of String theory ??, its math elegance it is not enough, and it's some kind similar to 'creationism' if there are no proof or counterproof to support a scientific theory we shouldn't support it (i believe more in LQG or Regge calculus rather than strings-made universe hope not to annoy anyone)
  2. jcsd
  3. Aug 3, 2007 #2


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    1. Can you specify more precisely in what sense more than 4dimesions are unstable?

    2. Let us assume that Penrose is correct. At best, this would prove that string theory (which lives in 10 dimensions, not 11, but this is not really important here) is unstable. However, being unstable is not the same thing as being wrong. For example, this could mean that FLAT spacetime in 10 dimensions is unstable. Then, if 6 extra dimensions are compactified, this could provide stability. But before speculating, we need first to have the answer to the question 1.
  4. Aug 3, 2007 #3

    George Jones

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    Actually, Penrose's claim is not specifically about sapcetimes that have dimension greater than 4.

    Penrose says that the Penrose-Hawking singularity theorem is vaild in (1+n)-dimensional spacetimes, not just in (1+3)-dimensional spacetimes. He says that although the spacetimes considered for string theory don't satisfy the conditions of the hypothesis of theorem, "generic" small perturbations of sting spacetimes can produce spacetimes that do satisfy the conditions of the theorem. Therefore, Penrose concludes that something catastropic must happen in these spacetimes, either in the compactified part, or in the "everyday" 1+3 part.

    Penrose admits that these conclusions are classical, but he doesn't think that quantum theory can save the day.

    I have no idea how these speculations have been received.
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