A Unique Theory of Gravity and Matter

The author has previously suggested that the ground state for 4-dimensional quantum gravity can be represented as a condensation of non-linear gravitons connected by Dirac strings. In this note we suggest that the low-lying excitations of this state can be described by a quasi-topological action corresponding to a trilinear coupling of solitonic 8-branes and 7-branes. It is shown that when the 7-brane excitations are neglected, the effective action can be interpreted as a theory of conformal gravity in four dimensions. This suggests that ordinary gravity as well as supersymmetric matter and phenomenological gauge symmetries arise from the spontaneous breaking of topological invariance.