Big Steve and the State of the Universe

Abstract

I share some reminiscences of the late Steven Weinberg. Then I discuss a topic in quantum field theory that he taught me: the role of state wave functionals in deriving the iϵ term of the Feynman propagator when using functional formalism. This is perhaps a curiosity for in–out scattering amplitudes on flat-space backgrounds, but it has much greater significance for the in–in amplitudes of the Schwinger–Keldysh formalism in cosmology. It also touches on the fate, about which Weinberg wondered, of the large logarithms one sometimes finds in quantum corrections from inflationary particle production.