Time in Cosmology

This chapter provides a self‐contained introduction to time in relativistic cosmology that clarifies how questions about the nature of time should be posed and the extent to which they have been or can be answered empirically. The first section of the chapter recounts the loss of Newtonian absolute time with the advent of special and general relativity, and the partial recovery of absolute time in the form of cosmic time in cosmological models. The second considers the beginning and end of time in a broader class of models in which there is not an analog of Newtonian absolute time. Reasonable physical assumptions imply that the universe is finite to the past, and the third section considers the “beginning” itself. The fourth section discusses the ramifications of the two recent debates of cosmology. The final section takes up the source of the asymmetry in people's experience of time.