Small-scale structure of spacetime as the origin of the gravitational constant

We suggest a means of incorporating the Planck length as a fundamental constant determined by the structure of spacetime. In this scheme the spacetime symmetry group is taken as the de Sitter group with radius of curvature proportional to the Planck length, but we argue that the effects of this curvature are not apparent at elementary-particle length scales. To make the connection with gravity we present a formulation of the gravitational interaction as the gauge theory of the de Sitter group. We obtain an action containing the Einstein-Cartan action, but in which the dimensional gravitational constant $G$ appears naturally as the consequence of the commutation relation of the de Sitter group. We also find a cosmological term, higherderivative couplings of the gravitational field, and a propagating torsion field, which we discuss.