Crisis in cosmology: Observational constraints on Omega and H

Abstract

This review of recent observations of cosmological interest seeks to take stock of how they constrain the standard hot big bang models with or without inflation. We look at two specific series indicative of this class of models. In one series the flatness condition of inflation requires that the density parameter shall be unity. Of late this statement has been relaxed somewhat to include the cosmological constant also as a contributor to the density parameter. Hence we ha»e used this "generalised" flatness condition. The other series of models does not need (be cosmological constant but assumes that the curvature parameter k = -1. Both these models are currently being pushed as "the" models of the universe. The observational constraints used by us are the measurements of the Hubble constant and the deceleration parameter, the ages of globular clusters, the abundance of primordial deuterium, the abundance of rich clusters, the baryon content of galaxy clusters and the abundance of high rsdshift objects. These constraints essentially limit the allowed values of the cosmological parameters. Our findings are that with measurements within their quoted error bars, the available parameter space has shrunk to negligible proportions. For survival of the standard models, therefore, one needs to take recourse to two normally unpalatable steps: (i) to doubt the existing error bars and hope to expand them and (ii) to fine-tone the theoretical parameters so that they fall within the available space. This is the essence of our perception of the crisis in cosmology.