Speaker
Description
General relativity and quantum field theory being the two most tested theories which explain exceedingly well the large scale structure and dynamics of spacetime on the one hand and the quantum properties of matter on the other, it is of no surprise that they form the theoretical basis for low energy perturbative quantum gravity experiments. Imposing self-consistency conditions between solutions of the Einstein equation and the field equations for quantum matter leads naturally to semiclassical gravity (SCG). However, when tackling quantum information issues, starting with as simple an entity as the entangled state between two masses (gravitational cat state), Einstein equation sourced by the expectation values of the stress energy tensor of quantum matter fields is inadequate. Correlations or fluctuations of mass densities enter as a necessity. The requisite theory is called stochastic semiclassical gravity. Introduced and constructed in the 90s, rooted in quantum field theory in curved spacetime of the 70s and SCG of the 80s, it has been applied to quantum field processes in the early universe and black holes where fluctuations phenomena are expected to play an important role. In this talk I shall summarize the key features of this theory and show how it, even in the nonrelativistic, weak field form, is needed for treating gravitational decoherence and entanglement problems (part 2), topics of rising current interest, as well as the effect of graviton noises on geodesic separations (part 3), all at experimentally accessible energies. Before that, in deference to the central theme of this conference which is (nonperturbative) quantum gravity, I want to share my view (part 1) and raise some questions of principle in the daunting quest for viable theories describing the microscopic structures of spacetime.
