  With the recent measurements of temperature and polarization anisotropies in
the microwave background by WMAP, we have entered a new era of precision
cosmology, with the cosmological parameters of a Standard Cosmological Model
determined to 1%. This Standard Model is based on the Big Bang theory and the
inflationary paradigm, a period of exponential expansion in the early universe
responsible for the large-scale homogeneity and spatial flatness of our
observable patch of the Universe. The spectrum of metric perturbations, seen in
the microwave background as temperature anisotropies, were produced during
inflation from quantum fluctuations that were stretched to cosmological size by
the expansion, and later gave rise, via gravitational collapse, to the observed
large-scale structure of clusters and superclusters of galaxies. Furthermore,
the same theory predicts that all the matter and radiation in the universe
today originated at the end of inflation from an explosive production of
particles that could also have been the origin of the present baryon asymmetry,
before the universe reached thermal equilibrium at a very large temperature.
  From there on, the universe cooled down as it expanded, in the way described
by the standard hot Big Bang model.
