From the abstract: "An action principle is described which unifies general relativity and topological field theory. An additional degree of freedom is introduced, and depending on the value it takes the theory has solutions that reduce it to (1) general relativity in the Palatini form, (2) general relativity in the Ashtekar form, (3) F Λ F theory...., (4) BF theory..." This is a new paper by Smolin and Starodubtsev, "General relativity with a topological phase: an action principle" posted yesterday, 18 November. http://arxiv.org/hep-th/0311163 [Broken] If anyone would care to elucidate any part of this, it would be much appreciated. Several of us (IIRC selfAdjoint, Ambitwistor, nonunitary...others?) have mentioned TQFT, BF theory. It would be really helpful if we had some entry-level description here clarifying basic things like "what is topological field theory" what makes it different, specifically topological, what are the connections to spin foams and other other current research areas (I know Baez has a good paper making the connection---but there has never been an summary of these things here at PF as far as I know.) Anyone have a few general words giving perspective on why Smolin/Staro's unification (by an action principle) is or is not interesting?