The 1998–2003 Revolution

This chapter looks at the change in the state of empirical cosmology in the five years from 1998 to 2003, which was great enough to be termed a revolution. It was driven by the two great experimental advances. The first is the measurement of the relation between the redshift of the spectrum of an object and its brightness in the sky, given its luminosity: the cosmological redshift–magnitude relation. The second is the detailed mapping of the angular distribution of the cosmic microwave background (CMB) radiation. The two programs reached the precision needed for significant constraints on cosmological models at essentially the same time. Quick acceptance of their interpretation was driven by the impressive consistency of implications of these two quite different ways to look at the universe and, equally important, by the consistency with other lines of evidence gathered in the years of research before the revolution.