My research field is observational cosmology, and focusses on the mystery of dark energy, the property of empty space that is causing the expansion rate of the universe to accelerate. Dark energy makes up approximately 70% of the energy density of the universe, yet we have few clues about its origin and nature. With colleagues at UM and elsewhere, I am participating in the Dark Energy Survey project, a 5000-square-degree optical survey of the southern sky using the 4-meter Blanco telescope at Cerro Tololo in Chile. With the data from this experiment, we hope to measure the acceleration of the universe over time in more detail, and possibly determine if the acceleration is due to Einstein's cosmological constant or some other mechanism. In the longer term, I hope to pursue this research through the space-based Joint Dark Energy Mission. Before becoming involved with dark energy research, I studied high-energy proton-antiproton collisions at the Fermilab Tevatron accelerator, and was a member of the team that discovered the top quark, the heaviest known elementary particle.