Order reduction in semiclassical cosmology

We investigate the Robertson-Walker cosmology with Lagrangian $R+{\alpha }_1\mathrm{\hslash }{R}^2+{\alpha }_2\mathrm{\hslash }{R}^{\mu \nu }{R}_{\mu \nu }+L_{rad}$ where $L_{rad}$ means classical source with traceless energy-momentum tensor. We weaken the self-consistence condition (L. Parker, J. Z. Simon, Phys. Rev. {D47}(1993),{1339}). Quantum corrections are expressed as contributions to the effective equation of state. We show that the empty space-time is stable within the class of radiation-filled expanding universes with no order reduction of the field equations.