General K=-1 Friedman-Lema\^itre models and the averaging problem in cosmology

Abstract

We introduce the notion of general K=-1 Friedman-Lema\^itre (compact) cosmologies and the notion of averaged evolution by means of an averaging map. We then analyze the Friedman-Lema\^itre equations and the role of gravitational energy on the universe evolution. We distinguish two asymptotic behaviors: radiative and mass gap. We discuss the averaging problem in cosmology for them through precise definitions. We then describe in quantitative detail the radiative case, stressing on precise estimations on the evolution of the gravitational energy and its effect in the universe's deceleration. Also in the radiative case we present a smoothing property which tells that the long time H^{3} x H^{2} stability of the flat K=-1 FL models implies H^{i+1} x H^{i} stability independently of how big the initial state was in H^{i+1} x H^{i}, i.e. there is long time smoothing of the space-time. Finally we discuss the existence of initial "big-bang" states of large gravitational energy, showing that there is no mathematical restriction to assume it to be low at the beginning of time.