Professor of Astrophysics, Princeton University
What is the universe made of? Recent observations suggest surprising new results. Not only most of the matter in the universe is dark and unconventional (non-baryonic) but, more surprisingly, the major component of the universe may be in the form of "dark energy" a form of energy that opposes the pull of gravity and causes the expansion of the universe to accelerate. By combining recent observations of clusters of galaxies, distant supernovae, and the cosmic microwave background radiation, we find evidence for an unexpected universeone that has only 5 percent "normal" matter, 20 percent dark matter, and 75 percent "dark energy." The observations indicate a universe that is lightweight, with sub-critical mass-density, and is dominated by a yet unknown "dark-energy." The observations and implications of the dark side of the universe will be discussed.