On homothetic cosmological dynamics

Abstract

We consider the homogeneous and isotropic cosmological fluid dynamics which is compatible with a homothetic, timelike motion, equivalent to an equation of state ρ + 3P = 0. By splitting the total pressure P into the sum of an equilibrium part Π and a non-equilibrium part II, we find that on thermodynamical grounds this split is necessarily given by p = ρ and Π = -4/3ρ, corresponding to a dissipative stiff (Zel'dovich) fluid.