(1977,1978) using adiabatic regularization methods, and Hartle (1977), Fischetti et al (1979) and Hartle and Hu (1979, 1980), using effective action methods. Their results on the effect of particle creation on anisotropy dissipation confirmed the qualitative estimate of Zel’dovich, and lent strong support for the viability of Misner’s chaotic cosmology program.

Entropy of Quantum Fields and Spacetime?
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These efforts in quantum field theory in curved spacetime and dissipative processes in the early universe contained the germs for two interesting directions of later development. Both involve quantum field theory and statistical mechanics applied to cosmological problems. They are\
i) Dissipation in quantum fields as a statistical thermodynamic proces s:\
Can one associate a viscosity with vacuum particle creation (Zel’dovich 1979, Hu 1984) like that of neutrino in the lepton era, or leptoquark boson decays in the GUT era? Can one define an entropy of quantum fields? (Hu and Pavon 1986, Hu and Kandrup 1987, Kandrup 1988)? An entropy of spacetime? (Penrose 1979, Hu 1983, Davies, Ford and Page 1986) Can one rephrase the chaotic cosmology idea in terms of some analog of second law of thermodynamics involving both fields and geometry (Hu 1983)? Can one generalize the fluctuation-dissipation relation (FDR) 