  We review different computation methods for the renormalised energy momentum
tensor of a quantised 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 renormalised 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.
