The launch of NASA’s Wilkinson Microwave Anisotropy Probe in June 2001 brought a new level of precision to cosmology. Scanning the whole sky, WMAP maps the minuscule departures of the cosmic microwave background from a perfectly isotropic, unpolarized 2.725-K blackbody radiator. The CMB’s parts-per-105 anisotropies and its parts-per-107 polarization are rich and precise indicators of fundamental properties of the cosmos.
Reports of the WMAP collaboration’s analysis of its first-year data in 2003 (see Physics Today, April 2003, page 21) confirmed, with unprecedented precision, the emerging “concordance model” inspired by an impressive variety of cosmological observations. 1 The Big Bang expansion, says the model, began with an inflationary epoch of exponential growth that stretched the cosmos by at least 22 orders of magnitude within 10–30 seconds. Some 14 billion years later, the model asserts, the cosmic mass–energy budget is now dominated by vacuum energy and nonbaryonic...
