Cosmic Microwave Background Observations in the Era of Precision Cosmology

The cosmic microwave background (CMB) radiation is a major arena for testing cosmological theories. Its discovery confirmed the hot-bigbang origin of the universe and ruled out the steady-state theory. Since that time the impact on cosmology of CMB studies has grown steadily, indicating the prevalence of non-baryonic matter and the existence of a negative pressure component in the 1980’s; the discovery of anisotropy in the 1990’s spurred a new generation of experiments and the entry into the era of precision cosmology in 2000 with the demonstration that the geometry is close to flat. The new “holy grail” of the field is the large-scale B-mode polarization component, which would reveal the energy scale of inflation. The sensitivity needed is ∼ 10 Kelvin, and at this level foreground polarized emission is likely to dominate over most of the sky. New radio-frequency cameras consisting of ∼1,000-element MMIC arrays will be deployed over the next few years on a wide variety of instruments and should bring about a revolution in radio astronomy with enormous consequences, not only for cosmology, but also for a wide variety of astrophysical studies.