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seen Dec 6 '12 at 10:56

Feb
17
awarded  Nice Question
Nov
20
comment Does the exact string theory $S$-matrix describe all physics there is?
Perhaps you are right, but you haven't explained what type of physical process I cannot describe with my exact S-matrix. I am not looking for hand-waving and general wisdom but a verifiable argument and/or a concrete example.
Nov
20
comment Does the exact string theory $S$-matrix describe all physics there is?
String theory is obviously not based on any approximation whatsoever. I did not ask what an S-matrix (in QFT) is usually used for. My question is conceptual and concerns string theory.
Nov
19
comment Does the exact string theory $S$-matrix describe all physics there is?
Perhaps you have a point, that's what I'm trying to find out. But you are not giving a coherent argument. Changing the momentum of just one particle is not a physically allowed process. At least you'd have to construct a physically possible process described in terms of actual observables (--> presumably S-matrix elements?!) and use that to show that there is something more to be learned...
Nov
19
comment Does the exact string theory $S$-matrix describe all physics there is?
That's obviously not true as there are matrix operators for the graviton which perturb the metric and hence the spacetime. That's the whole point why people got excited about strings, they include quantum gravitons in a dynamic theory. In principle it should be possible to obtain any dynamic spacetime background by appropriate vertex insertions, no? If this is not the case then I would be interested in hearing a rational argument why not.
Nov
19
comment Does the exact string theory $S$-matrix describe all physics there is?
Of course not, I asked about "all sensible questions about physics" which certainly includes cosmology, doesn't it? If you know the S-matrix "for any and all vertex operator insertions", as I supposed, that should allow for arbitrary moduli and geometries, no? If not, please explain why not.
Nov
19
awarded  Student
Nov
19
asked Does the exact string theory $S$-matrix describe all physics there is?