a real possibility for the idea of chaotic cosmology to work, now relying on quantum field processes effective near the Planck time ($10^{-43}$ sec from the Big Bang). One needs a new theory — the theory of quantum fields in curved spacetime. Actually this theory was just beginning to take shape through the work of Parker (1966, 1969) and Sexl and Urbantke (1968) at about the same time when Misner was working on the isotropy of the universe problem (1968). It was later realized that the reason why the Bianchi I universe and not the Robertson-Walker universe produces a copious amount of particles is because it breaks the conformal invariance of the theory (Parker 1973). Zel’dovich used a simple dimensional analysis to explain why the produced particles can strongly influence the dynamics of spacetime at the Planck time. The details are actually more involved than this, because one needs to remove the divergences in the energy-momentum tensor of the matter field before it can be used as the source of the Einstein equation to solve for the metric functions. This is what has been called the ‘backreaction’ problem. Zel’dovich and Starobinsky (1971) were the first to attempt such a calculation 