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No infinite gravitation in string theory?

  1. May 7, 2009 #1
    Combining quantum mechanics with general relativity supposedly yields infinite gravitation, between the gravitons if I have understood this correctly (correct me if I'm wrong). String theory supposedly does away with this infinite gravitation -- my question is, how does it do this? Furthermore, does string theory actually predict the existence of a graviton?

    Thank you. ^^
  2. jcsd
  3. May 8, 2009 #2


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    The infinities arise as a consequence of a certain mathematical tool, the perturbation series. It's like a Taylor expansion of a scattering amplitude; the small parameter is the coupling constant (Newton's constant).

    Due to some properties of GR one can show that the individual terms in this series become infinite. That's uggly, but not the core of the problem. These infinities are wel-known from QFT, but there they can be removed via renormalization. One can show that this FAILS in perturbatively quantized GR.

    In s.t. one expects that due to the topologically constraints for the string world sheet those infinities do not show up. As far as I know no proof to all orders exist but the s.t. community agrees that it will show up eventually.

    What I don't expect is that the perturbation series as a whole (the sum) is finite. I would say that this is not due to a failure in the fundamental theory but due to the perturbation expansion. This tool is overestimated because of its successes in particle physics. In a fundamental theory with non-perturbative treatment no infinities should arise; this should be true in s.t. and it is true in other QG approaches.
  4. May 8, 2009 #3
    to answer your second question, yes one of string theory's main appeals is that it predicts the existence of a massless spin-2 particle consistent with the graviton
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