Since the time that Einstein pioneered relativistic cosmology, the field of cosmology has been dominated by theoretical considerations that have ranged from straightforward applications of well-understood physics to some of the most fanciful ideas in all of science. However, in the last several years observational cosmology has taken the forefront. In particular, the results of recent observations on high-redshift supernovae and anisotropies in the radiation from the cosmic microwave background (CMB) have pinned down the major cosmological parameters to sufficient accuracy that a precise picture of our universe has now emerged. In this paper, we present this picture as currently suggested by the beautiful marriage of theory and experiment that now lies at the heart of modern cosmology.
We begin our discussion, in sections II and III, with a review of the standard theory of the present-day universe that persisted, virtually unaltered, from the time of Einstein until the mid 1990s. This review will lay most of the theoretical groundwork needed for sections IV and V on the two experimental efforts that has had such a major impact over the last few years. Once the new results have been explained, we present, in section VI, the picture of our universe that has emerged from the recent results. We then conclude this paper with some brief comments on the implications of these results for our understanding of not just the present-day universe, but of its past and future. To help make this discussion more accessible, we use SI units with time measured in seconds instead of meters and with all factors of G and c explicitly shown unless otherwise noted.