My research interests include cosmology, submillimeter and radio astronomy, astronomical instrumentation (especially for space flight), and the large-scale studies of the properties of the Milky Way galaxy.

I am the Principal Investigator (P.I.) of the Wilkinson Microwave Anisotropy Probe (WMAP) mission. WMAP was competitively selected in 1996 as a NASA medium-class Explorer (MIDEX) mission. WMAP was launched June 2001 and its first scientific results were made public in February 2003. WMAP quantified the age, content, history, and other key properties of the universe with unprecedented accuracy and precision. This was recognized by Science magazine as the 2003 "Breakthrough of the Year."

Previously I was the Deputy P.I. of the Differential Microwave Radiometers (DMR) instrument and a member of the Science Team of the Cosmic Background Explorer (COBE) mission. The COBE Differential Microwave Radiometers instrument was used to make the first detection of variations across the sky (anisotropy) of the temperature of the afterglow radiation from the Big Bang, the cosmic microwave background radiation.

I participate in NASA's Legacy Archive for Microwave Background Data Analysis (LAMBDA) data center. LAMBDA provides COBE, WMAP, and other cosmological data to the community.

It is widely believed that the infant universe underwent a rapid period of exponential expansion called "inflation." Gravitational waves are generically produced by inflation. Some day in the distant future those gravitational waves may be detected directly by a NASA "vision mission" called the Big Bang Observer. In the meantime, the gravitational waves may be detected by their imprint on the polarization of the cosmic microwave background radiation. NASA's "Beyond Einstein" program includes a mission called the Einstein Inflation Probe to detect the polarization pattern predicted from an inflationary epoch.

A mysterious dark energy is driving the accelerated expansion of the universe. The determination of the nature of the dark energy is a major goal of physics and cosmological research. Several groups are building and using instruments to probe the dark energy. A space mission, jointly sponsored by NASA and DOE, is planned. This Joint Dark Energy Mission (JDEM) is under study. I Co-Chair the JDEM Science Definition Team.