Saul Perlmutter

Saul Perlmutter is an American astrophysicist who teaches physics at the University of California, Berkeley, where he also holds the Franklin W. and Karen Weber Dabby Chair. He leads the International Supernova Cosmology Project at the Lawrence Berkeley National Laboratory. His most famous work—showing that the universe’s expansion is speeding up—won him the 2011 Nobel Prize in Physics, which he split with Brian P. Schmidt and Adam Riess. Perlmutter belongs to the American Academy of Arts & Sciences, the American Philosophical Society, and the National Academy of Sciences. Since 2021, he has been a member of the President’s Council of Advisors on Science and Technology.

Perlmutter grew up in Philadelphia’s Mount Airy neighborhood, attending Quaker schools in Germantown: Greene Street Friends School for elementary grades and Germantown Friends School through high school. He earned an AB in physics from Harvard, magna cum laude, in 1981, and a PhD in physics from Berkeley in 1986. His doctoral thesis, supervised by Richard A. Muller, was titled “An Astrometric Search for a Stellar Companion to the Sun.” In it, he built and used an automated telescope to look for Nemesis candidates, while also using that same telescope to search for supernovae—work that later led to his prize-winning cosmology. Perlmutter credits Luis Alvarez, a 1968 Nobel laureate, with the idea for an automated supernova search, which Alvarez shared with Perlmutter’s adviser.

At Lawrence Berkeley National Laboratory, Perlmutter heads the Supernova Cosmology Project. This team, along with the rival High-z Supernova Search Team led by Riess and Schmidt, found evidence that the universe’s expansion is accelerating, based on observations of distant Type Ia supernovae. A Type Ia supernova happens when a white dwarf star pulls enough extra mass from a companion star to exceed the Chandrasekhar limit. Because all such explosions are thought to occur in essentially the same way, they serve as standard candles: their intrinsic brightness is roughly constant. By measuring how bright they appear from Earth, researchers can calculate their distance. Comparing that distance to their redshift reveals both how far away and how fast the supernova is moving. The Supernova Cosmology Project found that these distant supernovae were receding faster than the Hubble expansion alone would predict, implying that the universe’s expansion has sped up over billions of years. The High-z Team reached a similar conclusion. Both teams’ papers appeared within weeks of each other, and the scientific community accepted the findings quickly because other theories supported them. Later evidence has backed up the result. This discovery revived research into the universe’s nature, especially dark energy. For this work, Perlmutter, Riess, and Schmidt shared the 2011 Nobel Prize in Physics.

Perlmutter is a lead investigator on the Supernova/Acceleration Probe project, which aims to launch a satellite dedicated to finding and studying more distant supernovae, with the goal of measuring how fast the universe has been accelerating more precisely. He also takes part in the Berkeley Earth Surface Temperature project, which seeks to better understand recent global warming by improving climate data analysis. He currently teaches at UC Berkeley.

Perlmutter’s awards include the 2002 Department of Energy’s E. O. Lawrence Award in Physics, the 2003 California Scientist of the Year Award, and the 2005 John Scott Award and Padua Prize. In 2006, he shared the Shaw Prize in Astronomy with Riess and Schmidt, and won the Antonio Feltrinelli International Prize. The following year, he and his team shared the Gruber Cosmology Prize (worth $500,000) with Schmidt and the High-z Team for discovering the accelerating universe. In 2010, he became a Miller Senior Fellow at UC Berkeley’s Miller Institute. In 2011, he and Riess were co-recipients of the Albert Einstein Medal. The Nobel Prize that year came with a SEK 10 million cash award (about US$1.5 million); Perlmutter received half, while Riess and Schmidt split the other half. In 2014, he received the Golden Plate Award from the American Academy of Achievement. In 2015, Perlmutter, Schmidt, Riess, and their teams shared the Breakthrough Prize in Fundamental Physics, with $3 million divided among them. A U.S. Department of Energy supercomputer, named Perlmutter, was commissioned in 2020 in his honor.