Can someone who understands it explain the significance of the Weinberg-Witten Theorem to the possibility of quantum gravity? (Described here: http://en.wikipedia.org/wiki/Weinberg-Witten_theorem) From the Wikipedia article, the conclusion is I don't understand how that can be correct. Deser and Feynmann (independently?) showed that General Relativity can be understood (at least in asymptotically flat spacetimes) as the field theory of a spin-2 massless particle whose source is the total stress-energy tensor. I know that this approach is not renormalizable, at least not in any obvious way, but it seems to conflict with the Weinberg-Witten Theorem. Is the WWT in some way a proof that the Deser/Feynmann theory is not renormalizable? One thing that is a little confusing about the Deser/Feynmann theory is exactly what the stress-energy tensor is. The assumption is that the spin-two particle couples to the total stress-energy, including the stress-energy of the particle itself. This is apparently very different from GR, in which the appropriate stress-energy tensor has no contribution due to gravity. I don't have a good grasp of how this is reconciled.