Quotes

General relativity and supergravity, in any Spacetime dimension greater than or equal to 2 + 1, can be written as gauge theories, such that the configuration space is the space of a connection field, Aa, on a spatial manifold Σ. The metric information is contained in the conjugate momenta. The gauge symmetry includes the diffeomorphisms of a Spacetime manifold, usually taken to be Σ x R. The dynamics takes a simple form that can be understood as a constrained topological field theory. This means that the action contains one term, which is a certain topological field theory called BF theory, plus another term which generates a quadratic constraint.

Lee Smolin (2008)