How Cosmic Structure Grew

Abstract

This chapter explores how the very evident departures from Albert Einstein's homogeneity—stars in galaxies in groups and clusters of galaxies—might have formed in an expanding universe. In the established cosmology, cosmic structure formed by the gravitational instability of the relativistic expanding universe. The early confusion about the physical meaning of this instability is an important part of the history. The chapter reviews these considerations, along with assessments of early scenarios of how cosmic structure might have formed. A theory of how the galaxies formed in the big bang cosmology has to provide a physically consistent picture of how cosmic structure evolved from the very different conditions in the early stages of expansion. That consideration is absent in the 1948 steady-state cosmology, so thinking about structure formation had to be different.