More Tools and Problems

Abstract

The central theme of the last chapter was the evolution of density perturbations under gravity in the expanding Universe. The attractive force of gravity and the opposing effect of the dark energy featured prominently in that analysis butwe nowneed to add in many more physical processes in order to create physically acceptable models for the formation of structure. In this chapter, the emphasis is upon the role of baryonic matter.We will spend a little time understanding why purely baryonic models of the formation of cosmic structures fail to account for the observations, supporting the view that the dominant dark matter must be in some non-baryonic form. We will develop the dark matter models in much more detail in Chap. 13, using many of the tools developed in this chapter. First of all, we need to deal with a number of key issues concerning cosmological horizons and superhorizon perturbations which we have glossed over so far.