Gravitational constants and the effective action in curved spaces

The author considers as quantum fields first a broken SU(5) Grand Unified Theory and then a pure nonabelian gauge theory in the limit of large curvature. In this second case he uses Renormalization Group methods to give the limit form of the effective action in closed form. In the last section of this work he considers a thought experiment which challenges the usual interpretation of the energy-time uncertainty relation. The issues raised by this experiment are closely related to the problem of the definition of particles in dynamical space-times