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Having looked through a few M-theory papers, I was absolutely flabbergasted to see that it's all still about taking something true and tried (path integrals), generalising it a little, and finding it might contain something like gravitons (which may not even exist). Wow! A theory of quantum gravity. Yeah, right.

When Einstein and Grossman were developing GR, did they focus their attention on classical field theory? No! The physical principles are

*everything*. In fact, it was Einstein's difficulty in accepting general covariance on physical grounds that held him up for years. General relativity is a 'background independent' theory. Until String theory comes to terms with the importance of this 100 year old physics it

*cannot possibly hope*to capture the essence of quantum gravity.

The fact that spin foam models are beginning to make contact with M-theory (see

John Baez & Urs Schreiber

Higher Gauge Theory: 2-Connections on 2-Bundles

http://www.arxiv.org/abs/hep-th/0412325 ) should start alarm bells ringing! And not just one of those 9V battery ceiling alarms, but a whole 1960's city of fallout shelter jobs.

After I pointed out that within category theory it was clear how to generalise twisted K-theory in a way relevant to physics, Urs Schreiber (the String theorist) replied that

*set theory has an answer, too*. This statement can hardly be refuted, to the satisfaction of the majority, until real proof is available, along the lines of a derivation of the fine structure constant, or something like that. One can point out, over and over again, that a very ordinary category of sheaves is, axiomatically, outside the realm of set theory. But as such objects may be discussed within set theoretic mathematics, they will be by those who believe that Strings (for instance) have reached a level of abstraction sufficient for unification. It is as if people are mesmerised by the thought

*we've been trying for 30 years now, and this maths is pretty cool, so we must be close now*. Nature, of course, really doesn't care very much about how much effort we've put in.

Quantum mechanics is about logic and axiomatics. So is sheaf theory. GR is about sheaf theory (twistors for instance). Quantum Gravity needs to get the logic right. Crazy? No! Bloody obvious!

:grumpy: