“Dark Energy and the Runaway Universe”

We expected the attractive force of gravity to slow down the rate at which the Universe is expanding. But in 1998, two essentially independent research teams made a Nobel-worthy discovery: since distant supernovae (exploding stars) appear fainter than predicted, the expansion of the Universe must be speeding up with time rather than decelerating. Over the largest distances, the Universe seems to be dominated by a mysterious, repulsive “dark energy” that stretches space itself faster and faster – a “runaway Universe.” The evidence for cosmic acceleration is now very strong, being supported by several independent techniques. Yet the physical origin and nature of dark energy, which makes up about 70% of the contents of the Universe, is not understood – and this may be the most important unsolved problem in all of physics, providing potential clues to a unified quantum theory of gravity. Our most recent surprise, however, is that the current expansion rate we measure with supernovae is faster than that predicted from observations of the young Universe, even taking into account the previously discovered acceleration. This suggests the possibility of exciting new physics beyond the standard model of cosmology.

About

Alex Filippenko, an elected member of both the National Academy of Sciences and the American Academy of Arts & Sciences, and an elected Fellow of the American Astronomical Society, is one of the world’s most highly cited astrophysicists. His scientific accomplishments, documented in more than 1000 research papers, have been recognized with numerous prizes. He was the only person to have been a member of both teams that revealed the accelerating expansion of the Universe, a discovery that was honored with the 2011 Nobel Prize in Physics to the teams’ leaders, as well as the 2007 Gruber Cosmology Prize and the 2015 Breakthrough Prize in Fundamental Physics to all team members. In 2017, he was selected for one of only two Caltech Distinguished Alumni Awards. Voted the “Best Professor” on the UC Berkeley campus a record 9 times, in 2006 he was named the Case/Carnegie National Professor of the Year among doctoral institutions, and in 2022 he received the American Astronomical Society’s Education Prize. He has produced 5 astronomy video courses with The Great Courses, coauthored an award-winning astronomy textbook, and appears in more than 120 television documentaries. He has given over 1000 public presentations, and he was awarded the 2004 Carl Sagan Prize for Science Popularization. An avid tennis player, hiker, runner, skier, whitewater rafter, snorkeler, and scuba diver, he enjoys world travel and experiencing total solar eclipses (18, so far).