Adiabatic vs. Isothermal: Two Pictures of Galaxy Origin

Abstract

It has become apparent in the last few years that many fundamental problems of cosmology will find their ultimate solution in the framework of recently formulated elementary particle interaction theories. Thus the question of why the initial conditions for galaxy formation were what they were will be answered by considering the earliest instants of cosmic evolution when the cosmic temperature exceeded the temperature for grand unification, or even earlier when we enter the domain of quantum gravity at the Planck time. Nevertheless, the period during which the cosmic temperature falls from ~ 10¹¹ °K to ~ 10 °K is of fundamental importance. It is the domain of well-established physics and from it we have learned the important relationship between cosmic nucleosynthesis and the microwave background radiation temperature. We have also learned a good deal about the evolution of inhomogeneities during this period, and hence this cosmic ‘middle age’ is an essential link between the Universe observed today and the era of ultra high energy physics.