Mass shell of the universe

The classical field equations of general relativity can be expressed as a single geodesic equation, describing the free fall of a point particle in superspace. Based on this formulation, a “world line” quantization of gravity, analogous to the Feynman-Schwinger treatment of particle propagation, is proposed, and a hidden mass-shell parameter is identified. We consider the effective action for the supermetric, which would be induced at one loop. In certain minisuperspace models, we find that this effective action is stationary for a vanishing cosmological constant. We also note that an interacting “particle” in superspace would propagate somewhat off shell, and suggest that a small deviation from the mass shell might be detectable (at least in principle) as a new source of decoherence.