The main part of scientific cosmology today deals with technical issues to do with modelling the origin and evolution of the universe, as discussed in the rest of this book. However cosmology also has wider connotations, as reflected in the broader use of the term in popular use. The link between these two aspects of cosmology resides in two interrelated issues: on the one hand, the relation between cosmology and local physics; and on the other, the foundational question of why the universe is as it is. Both can only be tackled properly by taking philosophical issues seriously. The underlying issue is fundamental: what is the nature of cosmology as a science? How does it relate to issues of testing and verification?

This book does not deal with these issues in depth, as to do so fully would take us too far from our main theme (and our competence), but it does not ignore them either, for to do so would exclude some of the most interesting issues in cosmology. This chapter considers, relatively briefly, how issues in relativistic cosmology relate to these two fundamental themes. It will emphasize two related key topics where these issues come to a head: namely the possible existence of a multiverse, and the question of whether the universe is probable or improbable.

We present theses that can be regarded as reasonable within the current framework of cosmology and physics.