  We derive a simple form for the propagator of a massless, minimally coupled
scalar in a locally de Sitter geometry of arbitrary spacetime dimension. We
then employ it to compute the fully renormalized stress tensor at one and two
loop orders for a massless, minimally coupled phi^4 theory which is released in
Bunch-Davies vacuum at t=0 in co-moving coordinates. In this system the
uncertainty principle elevates the scalar above the minimum of its potential,
resulting in a phase of super-acceleration. With the non-derivative
self-interaction the scalar's breaking of de Sitter invariance becomes
observable. It is also worth noting that the weak energy condition is violated
on cosmological scales. An interesting subsidiary result is that canceling
overlapping divergences in the stress tensor requires a conformal counterterm
which has no effect on purely scalar diagrams.
