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Portrait of Adam G. Riess
Photo: Holger Motzkau, Own work · CC BY-SA 3.0 via Wikimedia Commons

Nobel Prize in Physics · 2011

Adam G. Riess

He helped discover that the universe's expansion is speeding up, revealing that most of the cosmos is a mysterious dark energy.

The Nobel citation: “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae”
Born
December 16, 1969, Washington, D.C., USA
Shared with
Saul Perlmutter, Brian P. Schmidt
Affiliation at the time
Johns Hopkins University, USA; Space Telescope Science Institute, USA

Physics prize

2011

Shared with 2 other laureates.

Age that year

42years

Born in 1969.

Sources cited

22

Fact-checked September 24, 2026.

  • In fall 1997 his calculations said the universe's expansion was speeding up. Suspecting a simple error, he spent a couple of weeks rechecking and found none.
  • He emailed his team that the data required Einstein's cosmological constant on the eve of his honeymoon, two days after his January 1998 wedding.
  • His grandfather, the Jewish journalist Curt Riess, left Nazi Germany in 1933. His father, born in Berlin in 1931, reached the United States as a small boy in 1936.
  • At 13 he taught an adult class in computer programming. His parents also had him wash dishes and bus tables part-time at his father's deli.
  • As a graduate student he traded his group's future telescope time for slices of other observers' nights, building 22 supernova light curves from 1,200 observations.

The breakthrough

Discovering that the universe's expansion is speeding up

Since the 1920s astronomers have known the universe is expanding: galaxies are rushing away from each other. Most expected gravity to be slowing that expansion, the way a ball thrown upward slows before it falls back. Riess set out 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 are so bright and so alike that they work like standard light bulbs: if one looks dimmer than expected, it must be farther away. The catch is that they are not quite identical, and dust also dims them. As a Harvard graduate student Riess built a method, called MLCS, that used a supernova's colors and the way its light rose and faded to separate true distance from dust and from natural differences in brightness. In late 1997, working in the High-z Supernova Search Team led by Brian Schmidt, he analyzed 16 distant and 34 nearby supernovae with his method and a second one. The distant ones were 10 to 15 percent farther away than expected in a low-density universe without dark energy. The expansion was speeding up, as if the thrown ball shot off faster into the sky. The simplest explanation was Einstein's old cosmological constant: energy in empty space itself that pushes space apart, now called dark energy. Saul Perlmutter's rival team reached the same conclusion independently. Later, using the Hubble Space Telescope, Riess found supernovae old enough to show that the universe slowed down before it sped up, which ruled out dust as a trick of the light.[2],[3],[4],[9]

“Approach these results not with your heart or head but with your eyes. We are observers after all!”
Adam G. Riess, Email to his High-z team colleagues on 12 January 1998, sent on the eve of his honeymoon, urging them to trust the data showing an accelerating universe. He reproduced it in his 2011 Nobel Lecture.[4]

What it meant for humanity

Riess's discovery did not cure a disease or build a machine. It changed what humanity knows about the universe it lives in. Before 1998, most astronomers assumed that gravity was slowly braking the cosmic expansion that began with the Big Bang. The supernova results from Riess's team and from Saul Perlmutter's rival team showed the opposite. They revealed that about three quarters of the universe is a form of energy that nobody yet understands. Add the equally mysterious dark matter, and only about 5 percent of the universe is made of the ordinary atoms found in stars, planets and people. The finding also changed the forecast for the far future: if the acceleration continues, the universe will keep spreading out and growing colder rather than collapsing back on itself. Explaining dark energy is now one of the central problems in physics. Riess has pointed to big survey telescopes such as the Vera C. Rubin Observatory, NASA's Nancy Grace Roman Space Telescope and Europe's Euclid mission as the next tools for studying it. He kept sharpening the measurements himself. His SH0ES team used the Hubble Space Telescope to pin down today's expansion rate to within about 1.4 percent. They found it faster than the rate predicted from measurements of the infant universe, a mismatch now called the Hubble tension, which could point to physics beyond current theories. Other teams dispute how large the gap really is. Since 2007 Riess has also taught a popular Johns Hopkins course that introduces students of every major to the evolution of the cosmos. By 2016 its enrollment had doubled three times.

  • Science magazine named the discovery of the accelerating universe its Breakthrough of the Year for 1998.[3],[4]
  • The finding implies that about three quarters of the universe is dark energy, while ordinary matter, the stuff of stars, flowers and humans, makes up only about 5 percent.[2],[3]
  • Using Hubble, his team found supernovae so distant that they showed the universe slowing down before it sped up, ruling out cosmic dust as an alternative explanation.[4]
  • In 2022 his SH0ES team reported today's expansion rate as 73.04 plus or minus 1.04 km/s per megaparsec, sharply at odds with the value predicted from the early universe.[10]
  • Since 2007 he has taught a Johns Hopkins introduction to astronomy open to all majors; by 2016 its enrollment had doubled three times.[7]

Impact in numbers

Riess's contribution is knowledge about the universe, not a product, so we record no quantified claims. Working in Brian Schmidt's High-z team, and in parallel with Saul Perlmutter's rival team, he showed that the cosmic expansion is accelerating. That result led to today's standard picture of a universe dominated by dark energy. His own methods for correcting supernova brightness for dust and natural variation were central to his team's result, and his later Hubble work ruled out dust as an alternative explanation. His precision measurements of the Hubble constant have opened a live debate that may reveal either new physics or hidden measurement errors. The methods and people trained on these problems feed into space telescopes and large sky surveys, but putting a dollar value or a count of lives on that chain would be invention, not measurement.

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 Riess's work. It is basic research with no direct military or commercial use. The controversies are about credit and about the science itself. The Nobel Prize went to three people, yet the discovery came from two large teams. Riess's own Nobel Lecture credits many teammates, and the 2007 Gruber Cosmology Prize was shared by both teams. In 2016 three physicists argued that the supernova evidence for acceleration was weaker than claimed. Other researchers answered that errors in that analysis, and independent evidence from other methods, left acceleration secure. His later measurements of the Hubble constant are also contested. A team led by Wendy Freedman, using different kinds of stars, gets a lower expansion rate that fits the standard model of cosmology without any new physics.

  • Minor

    A team discovery credited to three people

    Riess's High-z team grew to about 15 members, and it built on supernova data from the Calan/Tololo survey in Chile. The Nobel went to just three people: the two team leaders, Schmidt and Perlmutter, and Riess. His lecture thanks many colleagues by name, and the 2007 Gruber Cosmology Prize was shared by both teams.[2],[4],[6]

  • Minor

    A challenge to the evidence for acceleration

    A 2016 paper in Scientific Reports argued that a much larger supernova sample could still fit a universe expanding at a steady rate. A reply by David Rubin and Brian Hayden identified errors in that analysis and noted that several independent methods confirm the acceleration.[12],[13]

  • Minor

    The Hubble tension is disputed

    Riess's SH0ES team reports a gap between today's measured expansion rate and the early-universe prediction. Wendy Freedman's Chicago-Carnegie team, using other types of stars observed with Hubble and Webb, finds values that fit the standard model without new physics.[10],[11]

Against the odds

Riess was born in Washington, D.C., in 1969 and grew up in suburban New Jersey. No source records antisemitism aimed at him. His hurdles were scientific, including a result so surprising that he first assumed it was an error. The persecution in his family story came a generation earlier. His grandfather, Curt Riess, was a Jewish journalist in Berlin who had written critically about the Nazis. After Hitler took power in 1933, he left Germany for Paris by way of Prague and Vienna, and in 1934 he moved on to the United States. Riess's father, Michael, born in Berlin in 1931, followed in 1936 as a small boy. A great-uncle studying for a chemistry doctorate at Rostock University was pushed out in the 1930s purge of Jews. That purge was national policy. In April 1933 Germany expelled Jews from the civil service and capped the number of Jewish students in schools and universities, and the 1935 Nuremberg Laws stripped Jews of their civil rights. By September 1939 about 282,000 Jews had left Germany. Escape was hard: by mid-1939, 309,000 German, Austrian and Czech Jews had applied for 27,000 places under the US immigration quota. Most Jews still in Germany when emigration was banned in 1941 were murdered in the Holocaust. Riess has said he learned some of his family's history only recently.

  • 1933

    Persecution

    After Hitler took power, Riess's grandfather Curt Riess, a Jewish Berlin journalist who had written critically about the Nazis, left Germany. He reached Paris by way of Prague and Vienna and moved to the United States in 1934.[14],[16],[17],[21]

  • 1936

    Exile

    His father, Michael, born in Berlin in 1931, emigrated to the United States aboard the liner Europa in 1936, according to his obituary. Riess has recalled the year as 1937.[14],[15],[20]

  • —

    Persecution

    A great-uncle was a doctoral student in chemistry at Rostock University until the purge of Jews in the 1930s forced him out of the program.[14],[21]

Jewish background

Jewish fatherRelationship to Jewish identity not documented

Riess's father, Michael Riess (1931-2007), was born in Berlin, the son of Ilse and the journalist Curt Riess. The Historical Dictionary of Switzerland records Curt Riess as Jewish. He left Nazi Germany in 1933, and Michael reached the United States in 1936. Riess has described this history, and a great-uncle forced out of a doctoral program at Rostock University in a purge of Jews. He said he learned some of it only recently. The sources we found say nothing about the background of his mother, the psychologist Doris Riess. Rabbis officiated at his 1998 wedding and at his sister's in 1989. We found no public statement from him about his own religious identity.[14],[15],[16],[17],[18],[19],[22]

Key dates

  1. 1933

    His grandfather Curt Riess, a Jewish journalist and critic of the Nazis, leaves Germany after Hitler takes power.[14],[16],[17]

  2. 1936

    His father, Michael Riess, born in Berlin in 1931, emigrates to the United States aboard the liner Europa.[15]

  3. December 16, 1969

    Born in Washington, D.C. He grows up in Warren, New Jersey, the son of a psychologist and an engineer turned businessman.[1],[6]

  4. 1992

    Graduates in physics from MIT, then begins a PhD in astronomy at Harvard under Robert Kirshner.[4],[8]

  5. 1996

    Earns his Harvard PhD with a new method for measuring supernova distances, then becomes a Miller Fellow at UC Berkeley.[2],[4]

  6. March 13, 1998

    Submits the High-z team paper, which he led and wrote, reporting evidence for an accelerating universe and a cosmological constant.[4],[9]

  7. December 1998

    Science magazine names the accelerating universe its Breakthrough of the Year.[3],[4]

  8. 1999

    Moves to the Space Telescope Science Institute in Baltimore.[1]

  9. 2004

    Publishes Hubble observations of very distant supernovae showing the universe slowed down before it began to speed up.[4]

  10. 2006

    Shares the Shaw Prize in Astronomy with Saul Perlmutter and Brian Schmidt.[6],[8]

  11. 2008

    Receives a MacArthur Fellowship.[6]

  12. October 4, 2011

    Awarded a quarter of the Nobel Prize in Physics, shared with Brian Schmidt and Saul Perlmutter, at age 41.[1],[2],[5],[6]

  13. July 2016

    Named a Bloomberg Distinguished Professor at Johns Hopkins University.[7]

  14. 2022

    His SH0ES team measures today's expansion rate with an uncertainty of about 1 km/s per megaparsec, sharpening the Hubble tension.[10]

Sources

  1. 1.Adam G. Riess - Facts · NobelPrize.org (Nobel Prize Outreach)
  2. 2.Press release: The Nobel Prize in Physics 2011 · NobelPrize.org (Royal Swedish Academy of Sciences), 2011
  3. 3.Popular information: The Nobel Prize in Physics 2011 · NobelPrize.org (Royal Swedish Academy of Sciences), 2011
  4. 4.Adam G. Riess - Nobel Lecture: My Path to the Accelerating Universe (8 December 2011) · NobelPrize.org (The Nobel Foundation), 2011
  5. 5.Adam G. Riess - Interview (telephone interview after the announcement, 4 October 2011) · NobelPrize.org, 2011
  6. 6.Astrophysicist Adam Riess Wins the 2011 Nobel Prize in Physics · Space Telescope Science Institute, 2011
  7. 7.Nobel laureate Adam Riess named 22nd Bloomberg Distinguished Professor at Johns Hopkins · Johns Hopkins University (The Hub), 2016
  8. 8.Adam Riess '92 wins Nobel Prize for physics · MIT News, 2011
  9. 9.Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant (Riess et al., Astronomical Journal 116:1009) · The Astronomical Journal (via arXiv), 1998
  10. 10.A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team (Riess et al.) · The Astrophysical Journal Letters (via arXiv), 2022
  11. 11.Status Report on the Chicago-Carnegie Hubble Program (CCHP): Measurement of the Hubble Constant Using the Hubble and James Webb Space Telescopes (Freedman et al.) · arXiv, 2024
  12. 12.Marginal evidence for cosmic acceleration from Type Ia supernovae (Nielsen, Guffanti and Sarkar) · Scientific Reports (via arXiv), 2016
  13. 13.Is the expansion of the universe accelerating? All signs point to yes (Rubin and Hayden) · The Astrophysical Journal Letters (via arXiv), 2016
  14. 14.Interview with Adam Riess: Nobel Laureate Adam Riess visits MIAPbP · Munich Institute for Astro-, Particle and BioPhysics (MIAPbP)
  15. 15.Michael Riess obituary (death notice) · The New York Times (via Legacy.com), 2007
  16. 16.Curt Riess, Author and Journalist, 90; Expert on Nazi Era · The New York Times, 1993
  17. 17.Riess, Curt (Rosmarie Zeller) · Historisches Lexikon der Schweiz (HLS), 2009
  18. 18.Weddings: Nancy Schondorf and Adam Riess · The New York Times, 1998
  19. 19.Dr. Gail Riess Is Married · The New York Times, 1989
  20. 20.German Jewish Refugees, 1933-1939 · United States Holocaust Memorial Museum, Holocaust Encyclopedia
  21. 21.Antisemitic Legislation 1933-1939 · United States Holocaust Memorial Museum, Holocaust Encyclopedia
  22. 22.Adam Riess · Wikipedia

Fact-checked on September 24, 2026 by a separate AI fact-checking pass that re-opened the sources, with 7 corrections made. How we check

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