for quantum processes in spacetimes with event horizons (Candelas and Sciama 1977, Mottola 1986) to general dynamical spacetimes? Indeed can one view the backreaction process as a manifestation of a generalized FDR for dynamical systems like quantum fields in cosmological spacetimes (Hu 1989, Hu and Sinha 1993)?

This first direction of research has been pursued in the eighties, with the infusion of ideas and techniques in statistical and thermal field theory. It is intended to be a generalization of thermodynamic ideas successfully applied to black hole mechanics (Davies 1978) to non-equilibrium quantum field systems characteristic of cosmological problems. This was an offshoot of Misner’s interest in dissipative processes in the early universe, only that one now takes on the challenge of doing everything with quantum fields in non-equilibrium conditions. This exercise probes into many deeper issues of thermodynamics and cosmology, such as the statistical nature of gravitational systems as different from ordinary matter, the thermodynamic nature of spacetimes (with or without event horizons), the nature of irreversibility and the cosmological origin of time-asymmetry. We will not belabor this direction of research here, but refer the reader to some recent reviews (Hu 1989, 1991, 1993a, 1993b). As we will see, inquiries 