The only finite mathematical framework that incorporates both the standard model of particle physics and gravity under one umbrella that I am aware of is string theory. I would like to know whether there are any other mathematical possibilities exist which do not depend on supersymmetry and still consistent with the standard model and gravity and produce finite answers. In a nutshell my question is: can there be any alternative to string theory? (Remember, I am not talking about only gravity. I am talking about gravity as well as other phenomena).
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So far, the answer seems to be no, but there is no mathematical proof. The main reason to believe that string theory is essentially unique is that it incorporates the holographic principle, the idea that the spacetime near and inside a black hole is emergent from the degrees of freedom of the black hole, and this idea is so difficult to imagine working, that it is hard to see some other solution.
Within string theory, the standard model emerges from either some matter, or from the Horava-Witten orbifold which produces an E8 gauge group in a circular compactification of M-theory. The E8 gauge group can naturally break to E6 and contains the standard model in a way as natural as SO(10) or U(5) (it is just a supergroup). So there is no difficulty embedding the standard model, but it is not predicted, just happens to work.
In other approaches, not only does the gravity not work well, the other stuff is not so natural as it is in string theory, where the total amount of stuff, like fields, gauge-groups, is constrained to be (of the right order but a few times bigger than) what we see.
The Loop Quantum Gravity folks have not been able to get elementary particle theory into their picture very well. They have been working with braids which have twists, which start to sound a bit like string to me. There seems to be a trend where all roads lead to string theory.