A concordant ‘freely coasting’ cosmology

Abstract

A strictly linear evolution of the cosmological scale factor is surprisingly an excellent fit to a host of cosmological observations. Any model that can support such a coasting presents itself as a falsifiable model as far as classical cosmological tests are concerned. Such evolution is known to be comfortably concordant with the Hubble diagram as deduced from data of recent observations of low and high redshift objects, it passes constraints arising from the age and gravitational lensing statistics, and clears basic constraints on nucleosynthesis. Such an evolution exhibits distinguishable and verifiable features for the recombination era. This article discusses the concordance of such an evolution in relation to minimal requirements for large-scale structure formation and cosmic microwave background anisotropies along with the overall viability of such models. While these results should be of interest for a host of alternative gravity models that support a linear coasting, we conjecture that a linear evolution would emerge naturally either from General Relativity itself or from a General Relativistic theory of a non-minimally coupled scalar field theory.