On the Newtonian cosmology equations with pressure

Abstract

The basic equations describing a Newtonian universe with uniform pressure are re-examined. We argue that in the semi-classical formulation adopted in the literature the continuity equation has a misleading pressure gradient term. When this term is removed, the resulting equations give the same homogeneous background solutions with pressure and the same long-wavelength growing mode solution for the density contrast as are obtained using the full relativistic approach.