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String theory classical limit?

  1. May 17, 2004 #1
    String theory "classical" limit?

    I know nothing about string theory, I'm still trying to deal with the more basic early 20th century stuff. But a question popped into my head which I hope someone can answer or point me to an answer.

    In general relativity you can recover Newtonian gravitational physics by applying the field equations to a slowly varying, weak gravitational field. In Maxwell's electrodynamics you can recover Coulomb's electrostatics law (I forget exactly how). In special relativity you can recover Newtonian mechanics in the limit as velocities go to zero.

    Can you do the same with string theory? Can you recover general relativity from string theory in some limit? What about quantum mechanics and quantum electrodynamics?
  2. jcsd
  3. May 17, 2004 #2


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    The string theorists say you can, but many relativitists disagree. String physics produces a graviton, and the properties of this graviton are such that, if matter particles exchange them, the resulting physics is like Einstein's general relativity, with som extra stuff that goes away at low energies.

    The trouble is that in most of the string models, all of this happens within a flat Minkowski spacetime. So you lose one of the cherished parts of general relativity, once called general covariance, now realized as diffeomorphism invariance. Space is decoupled from physics, which is business as usual in quantum physics, but a big loss for GR physics.
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