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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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I smell a dead horse, might be just me though. – user566 Feb 1 '11 at 3:15
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Just because we are not aware of a mathematical framework doesn't mean that one doesn't exist. If physicists had thought like this in 1900, quantum mechanics would never have been discovered. – Peter Shor Feb 1 '11 at 4:10
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I am not aware of any versions of string theory which contain the standard model. I think this is a common misconception fed by unrelenting publicity on the part of some. If there is some such framework I would love to know of it. – user346 Feb 1 '11 at 6:05
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Your question is about a topic that has seen broad and sometimes violate discussions over the last 10 years, with tons of papers and hundreds of participants. Therefore I don't think that this question can be appropriatly handled on this site. – Tim van Beek Feb 1 '11 at 9:12
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This is potentially interesting but I also don't like the formulation, it is very assuming and argumentative. Voting to close. – Marek Jul 31 '11 at 8:05
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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.

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Hi Ron. Maybe you should expand a bit and refute the comment of user346. Of course it depends on the definition of "contain" but my impression is that theorists use it in the sense that once the su2xsu3xu(1) is allowed in the theory one says that the standard model is "contained" in it. – anna v Apr 16 '12 at 7:08
@annav: I'll try. – Ron Maimon Apr 16 '12 at 12:08
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Thanks, this makes the answer complete – anna v Apr 16 '12 at 19:23
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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.

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statements such as "all roads lead to string theory" obscure the intricacy of the situation. You're correct that "braids" are something "stringy" but one could have said that of the edges of spin-networks. In fact Smolin argued for such a correspondence more than 13 years ago in Strings as perturbations of evolving spin-networks. Also as I mentioned in a comment above, I do not know of a string theory formulation which makes contact with the standard model or enables the calculation of scattering amplitudes for elementary particles. – user346 Feb 1 '11 at 6:09
... and since we're on the topic of matter in LQG let me mention my own work arXiv:1002.1462 where I present a proposal for how Bilson-Thompson's preons have a natural habitat in LQG or at least in a framework built using the same building blocks as LQG. – user346 May 2 '11 at 6:34

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