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Portrait of Saul Perlmutter
Photo: Holger Motzkau, Own work · CC BY-SA 3.0 via Wikimedia Commons

Nobel Prize in Physics · 2011

Saul Perlmutter

He tracked exploding stars billions of light-years away and found that the universe's expansion is speeding up, not slowing down.

The Nobel citation: “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae”
Born
1959, Champaign-Urbana, IL, USA
Shared with
Brian P. Schmidt, Adam G. Riess
Affiliation at the time
Lawrence Berkeley National Laboratory, USA; University of California, USA

Physics prize

2011

Shared with 2 other laureates.

Age that year

52years

Born in 1959.

Sources cited

27

Fact-checked September 24, 2026.

  • He set out in 1988 to measure how fast gravity was slowing the universe's expansion. A decade later his data showed the expansion is speeding up instead.
  • His grandfather welded in wartime shipyards and later ran a sandwich stand, while teaching Yiddish literature and history on the side. He taught young Saul Yiddish too.
  • Early on, his project got two and a half nights of good weather out of more than a dozen scheduled over almost two years at a telescope in Australia.
  • His team's first analysis of seven distant supernovae, published in 1997, found little sign of the force it would announce in January 1998.
  • A Department of Energy supercomputer at Berkeley Lab is named Perlmutter in his honor. He ran part of his Nobel-winning work on the same center's earlier machines.

The breakthrough

Discovering that the expansion of the universe is accelerating

Since the 1920s astronomers have known that galaxies are rushing apart: the universe is expanding. Nearly everyone expected gravity to be slowing that expansion, the way a ball thrown upward slows as it climbs. In 1988 Perlmutter co-founded a project to measure how fast it was slowing. His tool was the type Ia supernova, the explosion of a burnt-out star called a white dwarf. These blasts all peak at about the same brightness, and one can briefly shine as brightly as a whole galaxy. That makes them like light bulbs of known wattage: how dim one looks tells you how far away it is, and how far its light has been stretched toward red tells you how much the universe has grown since. The hard part was catching them. In any one galaxy these explosions are rare, often centuries apart, and each shines brightly for just a few weeks. His team built a wide-field digital camera and software that compared pictures of thousands of galaxies taken three weeks apart, so it could promise the world's biggest telescopes a batch of fresh supernovae on a set date. By 1997 the team had 42 distant ones, and they were fainter, so farther away, than a slowing universe allowed. The expansion was speeding up. A rival team reached the same answer independently in 1998. The cause, now called dark energy, makes up about three-quarters of the universe, and no one yet knows what it is.[2],[3],[4],[5],[13]

“I think this has to be the slowest "Aha!" in the history of science”
Saul Perlmutter, Telephone interview with NobelPrize.org on 4 October 2011, the day the prize was announced, describing how the surprising result sharpened over months of calibration.[6]

What it meant for humanity

Perlmutter's work did not cure a disease or build a machine. It changed what people know about the universe they live in. Before 1998 most astronomers assumed gravity was gradually braking the expansion that began with the Big Bang. His team and the rival High-z team showed that the expansion is instead speeding up. Combined with later measurements, it points to a universe that is about three-quarters dark energy, a form of energy no one understands. The atoms that make up stars, planets and people account for only about 5 percent, according to the Royal Swedish Academy of Sciences. The long-range forecast changed too: if the speed-up goes on, galaxies will keep drifting apart and the far future will be cold and dark. The finding set physics one of its biggest open problems. Perlmutter said in 2011 that theorists had been publishing roughly one paper a day on it for a decade, and in 2010 a National Academy of Sciences committee ranked a dark-energy space mission first among the new telescopes it wanted built. He has stressed that the discovery belonged to large teams working across continents, and that basic science rarely knows in advance what it will be good for. He has also tried to spread the habits of mind behind it. In 2013 he co-founded a Berkeley course on scientific-style reasoning. By 2024 it enrolled about 300 students, courses modeled on it had been adopted at Harvard, UC Irvine and the University of Chicago, and he had co-written a book based on it. In 2021 he joined the President's Council of Advisors on Science and Technology. A Department of Energy supercomputer now bears his name.

  • Together with later measurements, the discovery points to a universe that is about three-quarters dark energy. Ordinary matter, the atoms in stars, planets and people, makes up only about 5 percent.[3],[4],[5]
  • Science magazine named the accelerating universe its Breakthrough of the Year for 1998.[4],[8]
  • Perlmutter said in 2011 that theorists had published roughly one paper a day for ten years trying to explain what the supernova data showed.[6]
  • His course Sense and Sensibility and Science, begun at Berkeley in 2013, enrolled about 300 students in 2024. Courses modeled on it have been adopted at Harvard, UC Irvine and the University of Chicago.[10],[12]
  • The Perlmutter supercomputer, the flagship system at Berkeley Lab's national computing center, runs simulation, data analysis and AI work, including research on dark energy.[19]

Impact in numbers

Perlmutter's contribution is knowledge. With the rival High-z team he showed that most of the universe is a form of energy no one understands, overturning the expectation that gravity was slowing cosmic expansion and making dark energy one of the central problems in physics. The finding became part of cosmology's standard model, drew a flood of theoretical papers and helped motivate plans for new telescopes and a dedicated space mission to study it. It has no product, cure or dollar value, so we record no quantified claims; any number would be invented. Perlmutter himself has said that basic science cannot know in advance which discoveries will prove useful. His other legacy is teaching. His course and book on scientific-style reasoning aim to help students and voters weigh evidence, think in probabilities and admit error, and he brought that outlook to the President's Council of Advisors on Science and Technology.

Fundamental scienceSpaceEducation

No number is given here on purpose. Some contributions cannot be counted honestly, and we would rather describe them than invent a figure.

The double edge

No harms are documented from this discovery. It is basic research with no military or commercial use. The disputes around it concern credit and certainty. Perlmutter's team started first, in 1988, and presented its evidence at a January 1998 meeting. The rival High-z team, which included Adam Riess, announced matching results within weeks and submitted its journal paper about six months before Perlmutter's team did. The Nobel committee treated the two teams as independent discoverers. The prize named three people, while Perlmutter's team paper alone had 32 authors; later prizes, such as the 2015 Breakthrough Prize, were shared with the team members, and Perlmutter has stressed that the work was a team effort. A few researchers have also argued that the supernova evidence alone is weaker than claimed. A 2016 reanalysis of a much larger supernova catalog concluded that a steady, non-accelerating expansion still fit the data reasonably well. Other supernova researchers replied the same year that the reanalysis contained errors, and the Nobel committee noted that measurements of the cosmic microwave background and of galaxy clustering have independently confirmed the acceleration.

  • Minor

    Credit for a team discovery

    Two rival teams found the acceleration within weeks of each other. Perlmutter's team presented its evidence at a January 1998 astronomy meeting, but the High-z team submitted its paper first, in March 1998, six months ahead. The Nobel went to Perlmutter, Schmidt and Riess, while dozens of team members were named only in later prizes such as the 2007 Gruber and 2015 Breakthrough prizes.[5],[7],[13],[15],[16],[17]

  • Minor

    Questions about the strength of the supernova evidence

    A 2016 study in Scientific Reports reanalyzed a larger supernova catalog and concluded that a steady, non-accelerating expansion still fit the data reasonably well. A reply later that year in The Astrophysical Journal Letters identified errors in that analysis and found strong evidence for acceleration. The Nobel committee's scientific background notes that the cosmic microwave background and galaxy clustering independently support the acceleration.[5],[18],[27]

Against the odds

Perlmutter was born in 1959 and grew up in Philadelphia in a family of professors, and no source records antisemitism aimed at him. The hardship in his story belongs to his grandparents' generation. All four came to America as young adults early in the 20th century from Jewish towns and villages in Eastern Europe, and he describes them as poor but optimistic intellectuals. His mother's father, Samuel Davidson, was born in 1903 in Florești in Bessarabia, then a province of the Russian Empire inside its Pale of Settlement. Russia's 1882 May Laws brought repeated expulsions of Bessarabian Jews from villages. In 1903 a pogrom struck the Bessarabian city of Kishinev, and in 1905 a wave of pogroms across Bessarabia killed 108 Jews. Many impoverished Jews emigrated overseas. Davidson left for Canada at 16 and later settled in New York; in 1924 the United States sharply limited immigration from Eastern Europe. In America he welded in shipyards during World War II and later ran a sandwich stand, while teaching Yiddish literature and history as a self-taught scholar. One generation later his daughter was a professor. Perlmutter's own obstacles were scientific: bad weather, a skeptical mentor and a rival team racing for the same answer.

  • 1905

    Persecution

    His maternal grandfather was born in 1903 in Florești, Bessarabia, then under Russian rule. That year a pogrom struck the Bessarabian city of Kishinev, and in 1905 pogroms across Bessarabia killed 108 Jews. No source says the Davidson family itself was attacked.[21],[24],[25]

  • —

    Poverty

    His grandparents arrived as poor young immigrants. His maternal grandfather, a self-taught Yiddish scholar, earned his living welding in shipyards during World War II and later running a sandwich stand.[2]

  • 1919

    Other

    His maternal grandfather left Bessarabia for Canada at 16 and later settled in New York. In 1924 the United States sharply limited immigration from Southern and Eastern Europe, narrowing the route his grandparents' generation had taken.[21],[24],[26]

  • —

    Other

    Over almost two years at the start, his distant-supernova search got only two and a half nights of good weather out of more than a dozen scheduled at the Anglo-Australian Telescope, and even his mentor was skeptical of the project.[2]

Jewish background

Both parents JewishCulturally Jewish

All four of Perlmutter's grandparents came to the United States as young adults early in the 20th century from Jewish towns and villages in Eastern Europe. His mother's father, Samuel Davidson (1903-1989), was born in Florești in Bessarabia and taught in Philadelphia's secular Yiddish movement; he taught Saul and his sisters Yiddish language and culture. Perlmutter attended a Yiddish folkshul. His mother worked on Black-Jewish relations for Philadelphia's Jewish Community Relations Council. As an adult he has been a panelist at CLAL's Jewish Public Forum and a guest at the Davos Shabbat dinner. He writes that his grandparents hoped the modern world would leave religion behind.[2],[20],[21],[23],[24]

Key dates

  1. 1959

    Born in Champaign-Urbana, Illinois. He grows up in Philadelphia's Mount Airy neighborhood, the son of two professors.[1],[2],[3],[22]

  2. 1977

    Enters Harvard, torn between philosophy and physics. He chooses physics and graduates magna cum laude in 1981.[2],[9]

  3. 1986

    Earns his PhD at UC Berkeley in Richard Muller's group, where he wrote software that spotted supernovae in telescope images automatically.[2]

  4. 1988

    Co-founds, with Carl Pennypacker, the project that becomes the Supernova Cosmology Project, aiming to measure how fast the universe's expansion is slowing.[2],[5],[8]

  5. 1992

    Takes over leadership of the supernova group. By then the team has found a type Ia supernova at a then-record distance.[2]

  6. 1994

    His team shows it can find batches of distant supernovae on a pre-set date, so big telescopes can be booked in advance to study them.[2],[5],[7]

  7. 1997

    An analysis of the team's first seven distant supernovae shows little sign of a cosmological constant. By late 1997, a larger sample points the other way.[2],[14],[16]

  8. January 8, 1998

    Presents evidence that the expansion is accelerating at the American Astronomical Society meeting. The rival High-z team announces matching results within weeks.[2],[6],[16]

  9. December 1998

    Science names the accelerating universe its Breakthrough of the Year.[4],[8]

  10. October 4, 2011

    Awarded half of the Nobel Prize in Physics. Brian Schmidt and Adam Riess share the other half.[3],[9]

  11. 2013

    Launches Sense and Sensibility and Science, a Berkeley course on scientific reasoning, with a philosopher and a psychologist.[10],[12]

  12. 2015

    Shares the Breakthrough Prize in Fundamental Physics with Schmidt, Riess and members of both supernova teams.[17]

  13. September 22, 2021

    Appointed to the President's Council of Advisors on Science and Technology.[11]

  14. March 26, 2024

    Publishes Third Millennium Thinking, a book on using scientists' habits of thought in everyday decisions, with John Campbell and Robert MacCoun.[12]

Sources

  1. 1.Saul Perlmutter - Facts · NobelPrize.org (Nobel Prize Outreach)
  2. 2.Saul Perlmutter - Biographical · NobelPrize.org (Nobel Prize Outreach)
  3. 3.Press release: The Nobel Prize in Physics 2011 · NobelPrize.org (Royal Swedish Academy of Sciences), 2011
  4. 4.Popular information: Written in the stars (The Nobel Prize in Physics 2011) · NobelPrize.org (Royal Swedish Academy of Sciences), 2011
  5. 5.Scientific Background on the Nobel Prize in Physics 2011: The Accelerating Universe · Class for Physics, Royal Swedish Academy of Sciences, 2011
  6. 6.Saul Perlmutter - Interview (telephone interview after the announcement, 4 October 2011) · NobelPrize.org, 2011
  7. 7.Saul Perlmutter - Nobel Lecture: Measuring the Acceleration of the Cosmic Expansion Using Supernovae (8 December 2011) · NobelPrize.org, 2011
  8. 8.Saul Perlmutter (Berkeley Lab Nobel laureates) · Lawrence Berkeley National Laboratory, 2011
  9. 9.Saul Perlmutter Awarded 2011 Nobel Prize in Physics · UC Berkeley (Research UC Berkeley / Berkeley News), 2011
  10. 10.Saul Perlmutter - Faculty profile · UC Berkeley Department of Physics
  11. 11.President Biden appoints Saul Perlmutter, Inez Fung to science advisory council · UC Berkeley (Research UC Berkeley / Berkeley News), 2021
  12. 12.Amidst misinformation, critical thinking needs a 21st century upgrade · UC Berkeley (Research UC Berkeley / Berkeley News), 2024
  13. 13.Measurements of Omega and Lambda from 42 High-Redshift Supernovae (Perlmutter et al.; Astrophysical Journal 517, 565-586) · arXiv / The Astrophysical Journal, 1999
  14. 14.Measurements of the Cosmological Parameters Omega and Lambda from the First 7 Supernovae at z >= 0.35 (Perlmutter et al.; Astrophysical Journal 483, 565) · arXiv / The Astrophysical Journal, 1997
  15. 15.Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant (Riess et al.; Astronomical Journal 116, 1009-1038) · arXiv / The Astronomical Journal, 1998
  16. 16.The Acceleration of the Expansion of the Universe: A Brief Early History of the Supernova Cosmology Project (Gerson Goldhaber; AIP Conference Proceedings 1166, 53-72) · arXiv / AIP Conference Proceedings, 2009
  17. 17.Saul Perlmutter and the Supernova Cosmology Project Team - 2015 Breakthrough Prize in Fundamental Physics · Breakthrough Prize Foundation, 2015
  18. 18.Marginal evidence for cosmic acceleration from Type Ia supernovae (Nielsen, Guffanti and Sarkar; Scientific Reports 6, 35596) · Scientific Reports (Nature Portfolio), 2016
  19. 19.Perlmutter (NERSC flagship system) · National Energy Research Scientific Computing Center (NERSC), Berkeley Lab
  20. 20.Forward 50 2012: Saul Perlmutter · The Forward (archived at the Internet Archive), 2012
  21. 21.Samuel Davidson; Led Yiddish Culture Revival (Michael D. Schaffer, 5 December 1989) · The Philadelphia Inquirer (archived at the Internet Archive), 1989
  22. 22.Astrophysicist with Philly roots awarded Nobel Prize (Tom Avril, 4 October 2011) · The Philadelphia Inquirer (archived at the Internet Archive), 2011
  23. 23.Felice D. Perlmutter, 87, Temple University professor who spoke out on social issues · The Philadelphia Inquirer, 2019
  24. 24.Saul Perlmutter · Wikipedia
  25. 25.Bessarabia (from the Encyclopaedia Judaica) · Jewish Virtual Library (American-Israeli Cooperative Enterprise), 2007
  26. 26.The Immigration Act of 1924 (The Johnson-Reed Act) · Office of the Historian, U.S. Department of State
  27. 27.Is the expansion of the universe accelerating? All signs point to yes (Rubin and Hayden; Astrophysical Journal Letters 833, L30) · arXiv / The Astrophysical Journal Letters, 2016

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