The Wilkinson Microwave Anistotraphy Probe (WMAP), conceived in 1995 and launched in June 2001, was a follow-up to NASA's Cosmic Microwave Background Explorer (COBE), which, in 1992, discovered tiny (0.001 percent) variations in the intensity of cosmic microwave radiation across the sky. WMAP unveiled--with remarkable resolution--a seemingly absurd universe comprised of 0.5 percent visible matter (stars, dust, and gas), roughly 33 percent dark matter that holds the universe together, and roughly 66 percent mysterious dark energy that is accelerating the expansion of the universe. Fritz Zwicky, the eccentric Swiss-American astronomer based at Caltech, pointed out in the 1930s that the individual members of the Coma cluster of galaxies were moving too fast to be bound by the gravitational effects of their stars alone. The infusion of particle physics into cosmology in the 1980s brought a revolutionary idea: Dark matter may exist as particles of a new form of matter. The particle dark matter idea got a boost in 1998. The Super-Kamiokande detector in Japan, studying neutrinos produced in Earth's atmosphere by cosmic rays and in the interior of the Sun, showed that neutrinos have mass, albeit very little. INSETS: WMAP CLOSE-UP;GRAVITATIONAL LENSING.