Institute for Advanced Study Informal Astrophysics Seminar - TITLE ADDED

ABSTRACT: A decade since the realization that our universe's expansion is accelerating, the ball remains in the observationalists' court -- as the theorists look for more constraints on the parameter space.I will discuss some of the progress that has been made, and the prospects for upcoming advances, primarily focusing on the supernova measurements.The supernova measurements have improved dramatically, and I will show new evidence that that they have not yet reached their ultimate capability.Combined with the advances in the other techniques, we have the hope of distinguishing alternative explanations of the accelerating universe.The next big step calls for new facilities on the ground and in space.