Singularities and isotropy in a Brans-Dicke Bianchi-type VII universe

Abstract

We study the dynamical effects in the scale factors due to the scalar $ϕ$-field at the early stages of a supposedly anisotropic Universe expansion in connection with the problem of the initial singularity in the scalar-tensor cosmology of Jordan-Brans-Dicke. This is done by considering the behaviour of the general analytical solutions for the homogeneous model of Bianchi type VII in the vacuum case. We conclude that the Bianchi-VII$_0$ model shows an isotropic expansion and that its only physical solution is equivalent to a Friedman-Robertson-Walker spacetime whose evolution begins in a singularity and ends in another; moreover, we obtain that the general Bianchi-VII$_h$ (with $h\neq 0$) models show strong curvature singularities that produces a complete collapse of the homogeinity surfaces to a 2-plane, to a string-like one-dimensional manifold, or to a single point.