Abstract
We review different computation methods for the renormalized energy–momentum tensor of a quantized scalar field in an Einstein static universe. For the extensively studied conformally coupled case, we check their equivalence; for different couplings, we discuss violation of different energy conditions. In particular, there is a family of masses and couplings which violate the weak and strong energy conditions but do not lead to spacelike propagation. Amongst these cases is that of a minimally coupled massless scalar field with no potential. We also point out a particular coupling for which a massless scalar field has vanishing renormalized energy–momentum tensor. We discuss the backreaction problem and in particular the possibility that this Casimir energy could both source a short inflationary epoch and avoid the big bang singularity through a bounce.
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