We expected the attractive force of gravity to slow down the rate at which the Universe is expanding. But observations of very distant exploding stars (supernovae) show that the expansion rate is actually speeding up, an amazing discovery that was honored with the 2011 Nobel Prize in Physics to the teams’ leaders and the 2015 Breakthrough Prize in Fundamental Physics to all team members. Over the largest distances, the Universe seems to be dominated by a mysterious, repulsive “dark energy” that stretches space itself faster and faster. But the physical origin and nature of dark energy, which makes up about 70% of the contents of the Universe, is probably the most important unsolved problem in all of physics; it may provide clues to a unified quantum theory of gravity.
Alex Filippenko, an elected member of both the US National Academy of Sciences and the American Academy of Arts & Sciences, is one of the world's most highly cited astronomers. He is the recipient of numerous prizes for his scientific research, and he was the only person to have been a member of both teams that revealed the accelerating expansion of the Universe. Winner of the most prestigious teaching awards at UC Berkeley and voted the “Best Professor” on campus a record 9 times, he was named the US National Professor of the Year in 2006. He has produced 5 astronomy video courses with The Great Courses, coauthored an award-winning astronomy textbook, and appears in more than 100 television documentaries. In 2004, he was awarded the Carl Sagan Prize for Science Popularization.