My research focuses on cosmology and related issues of theoretical physics. I have done extensive work on the theory of the cosmic microwave background radiation and the ways in which it constrains our models of the universe. Current microwave observations, combined with optical observations of the large-scale galaxy distribution, cosmic abundances of light elements, and the supernova-1a Hubble diagram, combine to give tight constraints on the properties of the universe. The resulting "standard model" fits most observations well, but is troubling theoretically: our best guess says that only 4 percent of the universe's energy density is in the form of ordinary matter, 26 percent is made of as-yet undetected dark matter (which does not interact either via the strong or electromagnetic forces), and the remaining 70 percent is in an even stranger "dark energy", evenly distributed in space and having a negative effective pressure. Theorists have a number of good candidates for the dark matter particles, which are currently being pursued by many experimental groups, including the high energy experiment group at Pitt. Current ideas as to the nature of dark energy are all highly speculative.