A family shaped by exile
Adam Guy Riess was born on December 16, 1969, in Washington, D.C., to a Jewish family, and grew up in Warren Township, New Jersey. His father, Michael Riess, had served in the U.S. Navy and later ran a frozen-foods distribution company; his mother, Doris Riess, is a clinical psychologist. He has two sisters, the psychiatrist and author Gail Saltz and the artist Holly Hagerman.
His paternal grandfather was Curt Riess, a German Jewish journalist and writer born in Würzburg in 1902. Riess had been a sports writer, editor and film critic in Berlin, but in 1933 he was forced into exile by the Nazis. From Paris and then New York he wrote a stream of books and articles meant to help defeat Nazism, served as a specialist on Germany for the U.S. Navy and as an American war correspondent, and after the war wrote a biography of Joseph Goebbels. He later settled in Switzerland; more than a hundred book titles appear under his name.
Education and a talent for supernovae
Riess attended Watchung Hills Regional High School, graduating in 1988, and the New Jersey Governor’s School in the Sciences. He studied physics at the Massachusetts Institute of Technology, graduating in 1992 as a member of Phi Beta Kappa, and earned his PhD in astrophysics at Harvard University in 1996, supervised by Robert Kirshner and William Press.
His thesis tackled a practical problem. Astronomers hoped to use a type of exploding star, the type Ia supernova, as a “standard candle”: because these explosions are nearly identical, how bright one appears tells you how far away it is, just as you can judge the distance of a car from the brightness of its headlights. But they are not perfectly identical, and dust between us and the supernova dims its light. Riess measured more than twenty new supernovae and developed a method to correct for both the dust and the stars’ natural variations, making them far more accurate measuring tools. The thesis won the Astronomical Society of the Pacific’s Trumpler Award as one of unusual importance to astronomy.
How exploding stars measure the cosmos
A type Ia supernova is the explosion of a white dwarf, the compact remnant of an old star about as heavy as the Sun but as small as the Earth. When a white dwarf in a pair of stars pulls gas from its companion and grows to about 1.4 times the mass of the Sun, it can no longer hold itself up: runaway nuclear fusion tears it apart in seconds. Because these stars always blow up at about the same mass, the explosions are remarkably uniform, and for a few weeks a single one can shine as brightly as an entire galaxy, visible across billions of light-years.
They are also rare and fleeting. Across the visible universe about ten type Ia supernovae explode every minute, but in a typical galaxy there are only one or two in a thousand years. The teams therefore photographed the same patches of sky just after a new moon and again three weeks later, compared the images to find new specks of light, and then had to measure each candidate’s spectrum and changing brightness before it faded. Altogether the two teams found some fifty distant supernovae whose light was weaker than expected. The only sensible explanation was that they were farther away than a slowing universe would allow.
The race to weigh the universe
In 1996 Riess became a Miller Fellow at the University of California, Berkeley, and a key member of the High-z Supernova Search Team led by Brian Schmidt. The team, launched at the end of 1994, raced a rival group, Saul Perlmutter’s Supernova Cosmology Project, to find very distant supernovae and measure how the expansion of the universe had changed over billions of years. Both expected to find it slowing down, pulled back by the gravity of all the matter in the cosmos. By measuring how much it was slowing, they hoped, in effect, to weigh the universe.
Finding the supernovae required wide-field digital cameras that could photograph tens of thousands of galaxies at once, comparing images taken weeks apart to spot new points of light, then racing to the largest telescopes, including the new Keck telescope in Hawaii and the Hubble Space Telescope, before they faded. Riess later recalled that the director of the Space Telescope Science Institute, Bob Williams, thought the experiment so important that he gave both teams precious time from his own discretionary allocation.
The wrong sign
Shortly before his wedding, Riess did the final analysis of his team’s data. The answer had what he took to be the wrong sign: the distant supernovae were fainter than expected, which meant that the expansion of the universe was not slowing down but speeding up. “I remember thinking ‘Uh, I’ve made a terrible mistake, and I have to find this mistake’,” he told the Nobel Foundation, and he spent weeks searching for it. When he could not find one, he asked colleagues to check each step. Brian Schmidt, by then in Australia, did the final check and replied by email: “Well, hello Lambda,” the Greek letter for Einstein’s cosmological constant.
The discussion came to a head as Riess got married, and he famously answered colleagues’ emails on his honeymoon, to the dismay of his wife, Nancy. The team’s paper, Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant, appeared in the Astronomical Journal in 1998, with Riess as lead author. Perlmutter’s team reached the same result almost simultaneously, and the two independent findings were quickly accepted. Science magazine named the accelerating universe its Breakthrough of the Year for 1998.
Dark energy and the shape of our knowledge
If gravity alone were at work, the expansion of the universe should slow. That it is speeding up means that space is filled with something that pushes it apart, now called dark energy. According to the Nobel committee, dark energy makes up about three quarters of the universe, and together with the equally mysterious dark matter accounts for some 95 percent of it; the ordinary matter that makes up stars, planets and people is only about 5 percent. The committee called dark energy perhaps the greatest enigma in physics today.
The discovery also resolved existing puzzles, including an apparent paradox in which some stars seemed older than the universe itself: an accelerating universe is older than a decelerating one would be. In 2011 Riess shared the Nobel Prize in Physics with Perlmutter and Schmidt “for the discovery of the accelerating expansion of the Universe through observations of distant supernovae.” He has said that he finds the immensity of space not frightening but calming: “It just feels so big.”
Measuring the universe ever more precisely
In 1999 Riess moved to the Space Telescope Science Institute in Baltimore, the science centre for the Hubble Space Telescope, and later joined Johns Hopkins University, where he became a Bloomberg Distinguished Professor in 2016. From 2002 to 2007 he led a team that used Hubble to find dozens of supernovae so distant that they showed the universe had been decelerating before it began to accelerate, confirming the discovery and ruling out alternative explanations.
Since 2005 he has led the SH0ES team, which measures the Hubble constant, the current expansion rate of the universe, with a precision approaching 1 percent. Its measurements disagree with the rate predicted from the cosmic microwave background using the standard model of cosmology, a discrepancy known as the Hubble tension. Riess’s data have prompted further tests of whether the standard model of cosmology still describes the universe adequately, or whether the tension points to new physics. He has repeatedly been listed among the top 1 percent of most-cited researchers in his field.
Jewish heritage
Riess grew up in a Jewish family in suburban New Jersey, the grandson of a German Jewish exile whose career had been upended by Nazism and who spent the war years writing against it. The Jewish Virtual Library describes him as a Jewish American astrophysicist, and he is counted among Jewish Nobel laureates in physics.
He has not spoken much in public about religious practice. His story connects two very different twentieth-century Jewish experiences: a grandfather driven from Germany in 1933, and a grandson raised in American security who could devote his life to measuring the universe.
Honours and legacy
Besides the Nobel Prize, Riess shared the 2006 Shaw Prize in Astronomy with Perlmutter and Schmidt, shared the 2007 Gruber Cosmology Prize and the 2015 Breakthrough Prize in Fundamental Physics with his team, received a MacArthur Fellowship in 2008 and was elected to the National Academy of Sciences in 2009. He is married to Nancy Joy Schondorf; they have two children, Noah and Gabrielle. Earlier he had won the American Astronomical Society’s Helen B. Warner Prize in 2003 and the Raymond and Beverly Sackler Prize in Physics in 2004 for the discovery of cosmic acceleration, and in 2020 he was made a fellow of the American Astronomical Society.
Adam Riess’s contribution is knowledge of the most basic kind: what the universe is made of and where it is going. His careful methods turned exploding stars into reliable rulers, his willingness to trust a surprising result revealed dark energy, and his ongoing measurements keep testing whether our best theory of the cosmos is complete. The questions he opened now guide space missions, telescopes and the work of thousands of scientists worldwide.
Sources & further reading
Adam G. Riess, Facts and Telephone interview, NobelPrize.org · Popular information: The Nobel Prize in Physics 2011, NobelPrize.org · Discovering dark energy and the Hubble tension: extended interview with Adam Riess, GBH Particles of Thought (NOVA) · Johns Hopkins University professor shares Nobel Prize in Physics, CBS News Baltimore · Adam Riess, Jewish Virtual Library · Adam Riess, Wikipedia · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.