Alex Filippenko presents a public talk at UC Berkeley on June 20, 2009, in celebration of the International Year of Astronomy, as part of the series described at http://astro.berkeley.edu/iya . Observations of very distant exploding stars (supernovae) show that the expansion of the Universe is now speeding up, rather than slowing down due to gravity as expected. Other, completely independent data strongly support this amazing conclusion. Over the largest distances, our Universe seems to be dominated by a repulsive "dark energy" -- an idea Einstein had suggested in 1917, but renounced in 1929, anecdotally as his "biggest blunder." Dark energy stretches the very fabric of space itself faster and faster with time. But the physical origin of dark energy is unknown, and is often considered to be the most important unsolved problem in physics; it probably provides clues to a unified quantum theory of gravity.
Alex Filippenko is one of the world's most highly cited astronomers, and the recipient of numerous prizes for his research. He was a member of both teams that discovered the accelerating expansion of the Universe; this was named the "Top Science Breakthrough of 1998" by Science magazine, and the teams received the 2007 Gruber Cosmology Prize for their discovery. Prof. Filippenko has won the highest teaching awards at UC Berkeley, where the student body has voted him the "Best Professor" on campus six times, and he was selected as the 2006 Carnegie/CASE National Professor of the Year among doctoral institutions.
Videography and editing by Chris Klein. This video is released under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License - http://creativecommons.org/licenses/by-nc-sa/3.0/us