Milne spacetime is just a part of Minkowski, written in weird coordinates that look like expanding Friedman-Robertson-Walker with spatial hypersurfaces of negavie 3D curvature. I've seen papers where they calculate the renormalized energy momentum tensor in Milne spacetime for (a) a conformally coupled scalar field (b) in the so called adiabatic vacuum state |0> The renormalized tensor <0|T_munu|0> contains two terms called vacuum polarization and particle creation. They cancel each other to zero which leads the often seen statement 'there isn't particle creation in Milne universe' which makes sense since it is part of Minkowski. I don't understand if the renormalized tensor still vanishes for a scalar field that is NOT conformally coupled to gravity or a quantum state of the field that is a vacuum but not the adiabatic vacuum. Anyone know articles that address that?