One of today's most pressing open questions in physics concerns the nature of the dark energy driving the accelerating expansion of the Universe. Although there is currently little doubt that dark energy represents some new and fundamental physics, there is still a need to distinguish between various possibilities for its nature: is it gravitational, residing in Einstein's cosmological constant, or exotic matter, coming from quantum mechanical processes in the vacuum? This project continues an ambitious survey, currently about half complete, to use some 200 Type Ia supernovae between redshifts of 0.2 and 0.8 to map out the expansion history of the Universe. It should be able to constrain a critical dark energy parameter with a fractional uncertainty of only 10%.
Many undergraduate and graduate students have been involved in this cutting-edge research project, and the enhanced capabilities it required at an NSF-supported telescope have benefited all users of that facility. Since the nature of the dark energy is a mystery that has captivated the imagination of the general public, project members will continue to be very engaged in both formal and informal educational activities on this topic.
