Spacetime metric and lightcone fluctuations

Several aspects of the quantum fluctuations of spacetime geometry are discussed. A model for lightcone fluctuations is described in which a bath of gravitons leads to metric fluctuations. The operational definitions of such phenomena as lightcone and horizon fluctuations are examined. The problem of describing fluctuations of a quantum stress tensor is also discussed. The possibility that one can gain some insights about spacetime geometry fluctuations from studies of the force fluctuations on material bodies is suggested.