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Thread: My top 10 string theory questions

  1. #1 My top 10 string theory questions 
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    My top 10 string theory questions
    Here is what I consider the top 10 questions in string theory* (not necessarily in order of importance). They are not the obvious questions, like, "What is the value of this constant, and why?" but questions so hard that they are usually ignored, or even assumed to be already answered (e.g., by adding "How...” to the beginning).
    1. Is spacetime four dimensional? It sure looks that way. Also, 4 is the "critical" dimension of quantum field theory.
    2. If not, does compactification work? What forces the extra dimensions to hide, and prevents them from reappearing? Do the extra dimensions really do anything we couldn't reproduce without them? Does compactification destroy predictability?
    3. Does string theory work? Perturbative finiteness seems to be the only reason for it, but even in quantum field theory problems fixed at the perturbative level is known to return nonperturbatively. Is this what happens with the nonperturbative eleventh dimension, which is described by nonrenormalizable membrane theory?
    4. If so, is a 10-dimensional perturbation expansion reasonable for an 11-dimensional theory? I'd like to see a 3-dimensional approach to 4-dimensional particle physics.
    5. Are there any other strings than the D=10(11) and 26 ones? Dual theories only count once.
    6. Is super symmetry useful? Is fine tuning really that much worse than any other kind of tuning? Are nonminimal Higgs's any worse than super partners? (Where are those Higgs anyway?)
    7. Is the graviton fundamental? Oddly enough, it doesn't look that way in open string theory. But if not there, maybe elsewhere...
    8. Do black holes exist? We have evidence of gravitational fields strong enough to be associated with black holes theoretically, but not of the event horizons that define black holes.
    9. If so, what do you do with the singularities? People worry about information loss from event horizons, but doesn't a singularity signify breakdown of the theory?
    10. Does confinement work? This is really a string theory question, since strings were originally proposed to describe hadrons. By "work", I mean I want to actually calculate the observed linear Regge trajectories that define the string, not just some constants characterizing low-energy behavior (Chiral symmetry breaking, etc.), and see what happens to the bound states as their excitation energy increases.


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