Adam Riess

Adam Riess
Born	Adam Guy Riess 16 12, 1969
Birthplace	Washington, D.C., U.S.
Nationality	American
Occupation	Astrophysicist, professor
Known for	Accelerating expansion of the universe, dark energy, Hubble constant
Education	Harvard University (PhD) Massachusetts Institute of Technology (BS)
Spouse(s)	Nancy Joy Schondorf (m. 1998)
Awards	Nobel Prize in Physics (2011) Shaw Prize in Astronomy (2006) MacArthur Fellowship (2008)

Adam Guy Riess (born December 16, 1969) is an American astrophysicist who serves as a Bloomberg Distinguished Professor at Johns Hopkins University and the Space Telescope Science Institute. His career has been defined by a singular pursuit — using the light of distant supernovae to measure the fate of the cosmos — a pursuit that led to one of the most surprising discoveries in the history of science: the accelerating expansion of the universe. For this work, Riess shared the 2011 Nobel Prize in Physics with Saul Perlmutter and Brian Schmidt, a recognition that came when Riess was just 41 years old. He had begun the foundational research at the age of 27. In more recent years, Riess has been at the center of a growing scientific debate known as the "Hubble tension," a discrepancy between different methods of measuring the universe's expansion rate that has prompted fundamental questions about whether the Standard Model of cosmology still adequately describes the universe. His sustained contributions to observational cosmology have earned him numerous honors, including the Shaw Prize in Astronomy (2006), a MacArthur Fellowship (2008), and election as a Fellow of the American Astronomical Society (2020).

Early Life

Adam Guy Riess was born on December 16, 1969, in Washington, D.C. He grew up in Warren, New Jersey, a community in the northern part of the state. His family background included notable figures in journalism; his distant relative Curt Riess was a German-American author and journalist who was an expert on the Nazi era and who died in 1993 at the age of 90.

Riess grew up in a family that valued education and intellectual inquiry. His father was a naval engineer and his mother was a clinical psychologist. He attended Watchung Hills Regional High School in Warren Township, New Jersey, where he developed his early interests in science and mathematics.

From a young age, Riess demonstrated an aptitude for the physical sciences. His curiosity about how the universe worked would eventually lead him to pursue a career in astrophysics, a field that was undergoing rapid transformation in the late twentieth century as new observational technologies made it possible to probe the deepest reaches of space with unprecedented precision.

Education

Riess enrolled at the Massachusetts Institute of Technology (MIT), where he earned his Bachelor of Science degree in physics. At MIT, he received a rigorous grounding in theoretical and experimental physics that prepared him for graduate research in observational cosmology.

He subsequently pursued doctoral studies at Harvard University, where he worked under the supervision of Robert Kirshner and William H. Press. His doctoral dissertation, completed in 1996, was titled "Type Ia Supernova Multicolor Light Curve Shapes" and focused on developing methods to use Type Ia supernovae as precise distance indicators in cosmology. This work established the technical foundation — a method called the Multicolor Light Curve Shape (MLCS) technique — that would prove essential to his later discovery of the accelerating universe. The MLCS method allowed astronomers to account for variations in the brightness and color of Type Ia supernovae, thereby reducing the scatter in distance measurements and making them far more reliable as "standard candles" for measuring cosmic distances.

Career

Discovery of the Accelerating Universe

After completing his PhD at Harvard in 1996, Riess began postdoctoral work at the University of California, Berkeley, where he became a key member of the High-z Supernova Search Team led by Brian Schmidt. The team's objective was to use observations of distant Type Ia supernovae to measure the rate at which the expansion of the universe was decelerating — a deceleration that was expected due to the gravitational pull of all the matter in the universe. The prevailing expectation among cosmologists at the time was that the expansion, set in motion by the Big Bang, would be slowing down.

Riess was 27 years old when he began leading the data analysis for the team. In 1998, his analysis of observations of distant supernovae produced a result that contradicted all expectations: the expansion of the universe was not slowing down at all but was in fact accelerating. The supernovae were dimmer than expected, meaning they were farther away than predicted by models assuming a decelerating universe. This finding implied the existence of an unknown form of energy — later termed "dark energy" — that was pushing the universe apart at an ever-increasing rate.

The discovery, published in 1998, was simultaneously and independently confirmed by the Supernova Cosmology Project led by Saul Perlmutter at Lawrence Berkeley National Laboratory. The converging evidence from two independent teams gave the result exceptional credibility and sent shockwaves through the physics community. The finding was named the "Breakthrough of the Year" for 1998 by Science magazine.

The implications were profound. Dark energy appeared to constitute approximately 68 percent of the total energy content of the universe, yet its fundamental nature remained — and continues to remain — unknown. The discovery reshaped cosmology and established a new standard model of the universe known as the Lambda-CDM model, in which the cosmological constant (lambda) represents the dark energy driving the accelerated expansion.

Riess's observations, along with those of the competing team, provided direct evidence that "shocked even him," as later described in public lectures and interviews.

Career at Johns Hopkins University and the Space Telescope Science Institute

Following his postdoctoral work, Riess joined the faculty of Johns Hopkins University. He also holds a position at the Space Telescope Science Institute (STScI), which is located on the Johns Hopkins campus in Baltimore, Maryland, and serves as the science operations center for the Hubble Space Telescope and the James Webb Space Telescope.

In 2016, Riess was appointed as a Bloomberg Distinguished Professor at Johns Hopkins, a designation established through a $350 million commitment from Michael R. Bloomberg to the university announced in 2013. The Bloomberg Distinguished Professorships are interdisciplinary appointments designed to bring together scholars from different departments and schools within the university. In Riess's case, the appointment bridges the Krieger School of Arts and Sciences and the Whiting School of Engineering.

At Johns Hopkins and STScI, Riess has continued his research program using supernovae as cosmological probes. He has led major observational campaigns using the Hubble Space Telescope to refine measurements of the Hubble constant — the rate at which the universe is expanding — with ever-increasing precision. His team, known as SH0ES (Supernova H0 for the Equation of State), has systematically worked to reduce uncertainties in the cosmic distance ladder, a chain of methods used to measure distances to ever-more-remote objects in the universe.

Among his notable doctoral students is Daniel Scolnic, who has become a prominent researcher in supernova cosmology in his own right.

The Hubble Tension

In more recent years, Riess's research has brought him to the forefront of one of the most significant open questions in modern cosmology: the Hubble tension. This refers to a persistent and statistically significant discrepancy between two methods of measuring the Hubble constant (H₀), the parameter that describes how fast the universe is currently expanding.

Riess's team, using observations of Cepheid variable stars and Type Ia supernovae in the nearby universe, has consistently measured the Hubble constant to be approximately 73 kilometers per second per megaparsec (km/s/Mpc). However, measurements derived from observations of the cosmic microwave background (CMB) — the remnant radiation from the early universe — by the European Space Agency's Planck satellite yield a value of approximately 67.4 km/s/Mpc when interpreted through the standard Lambda-CDM cosmological model.

The discrepancy between these two values has grown more statistically significant as measurement techniques have been refined on both sides. By the mid-2020s, the tension had reached approximately 5 sigma — a level of statistical significance that in particle physics would typically be considered sufficient to claim a discovery. This has prompted intense debate in the cosmological community about whether the discrepancy points to new physics beyond the standard model of cosmology, or whether it might be attributable to systematic errors in one or both measurement methods.

Riess has been a central figure in this debate, consistently arguing that his team's local measurements are robust and that the tension is real. He has stated that his data has "prompted questions and further testing to determine if the Standard Model still adequately describes the universe." In a 2025 interview with The Atlantic, Riess discussed the implications of the Hubble tension, suggesting that the discrepancy could signal that the universe contains unknown physics — perhaps a new form of dark energy, a previously unknown particle, or some other phenomenon not accounted for in current models.

The James Webb Space Telescope (JWST), which began science operations in 2022, has provided an important new tool for testing these measurements. Early JWST observations have largely confirmed the Hubble Space Telescope's measurements of Cepheid distances, strengthening the case that the tension is not the result of calibration errors in the local distance ladder.

However, the debate continues to evolve. In late 2025, some researchers raised the question of whether certain aspects of the measurements of the accelerating expansion itself might need re-examination, adding new layers of complexity to the ongoing discussion.

Public Engagement and Lectures

Riess has been active in communicating his research to the public. He has delivered lectures at universities and scientific institutions around the world, explaining the discovery of dark energy and the implications of the Hubble tension to general audiences. In May 2025, he gave a lecture at the University of Wisconsin–Madison that was described as a "packed lecture" in which he "discussed how his research rewrote the fundamental story of the universe."

In April 2025, he delivered the Dirac Lecture at Florida State University, sharing "the latest research into the expanding universe" in a public lecture format. In September 2025, he participated in a public discussion at Pioneer Works in Brooklyn, New York, as part of the "Scientific Controversies" series on the expansion of the universe. In December 2025, he sat for an extended interview with PBS NOVA in which he discussed both the discovery of dark energy and the Hubble tension.

In 2026, Riess was invited to deliver a public lecture as part of the PASCOS (Particles, Strings, and Cosmology) 2026 conference at the University of Sheffield in the United Kingdom.

Personal Life

Adam Riess married Nancy Joy Schondorf in 1998. Their wedding was reported in The New York Times. The couple resides in Baltimore, Maryland, where Riess is based at Johns Hopkins University.

Riess has spoken in interviews about the experience of making a discovery that overturned fundamental assumptions about the universe. In a 2013 interview with NPR, he discussed the process and personal impact of his scientific work.

Recognition

Riess has received numerous awards and honors for his contributions to astrophysics and cosmology.

In 2006, Riess shared the Shaw Prize in Astronomy with Saul Perlmutter and Brian Schmidt for their discovery of the accelerating expansion of the universe. The Shaw Prize, awarded by the Shaw Prize Foundation in Hong Kong, is sometimes referred to as the "Nobel of the East" and carries a substantial monetary award.

In 2008, Riess received a MacArthur Fellowship, commonly known as a "genius grant," from the John D. and Catherine T. MacArthur Foundation. The fellowship is awarded to individuals who show exceptional creativity and promise for continued achievement.

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." Riess and Schmidt shared one half of the prize for their work with the High-z Supernova Search Team, while Perlmutter received the other half for his leadership of the Supernova Cosmology Project. At 41, Riess was among the younger recipients of the Nobel Prize in Physics in recent decades.

Riess has also received a Golden Plate Award from the Academy of Achievement.

In 2020, Riess was named a Fellow of the American Astronomical Society, in recognition of his contributions to the field of astronomy and astrophysics.

Legacy

Adam Riess's contributions to cosmology have fundamentally altered the scientific understanding of the universe. The 1998 discovery that the expansion of the universe is accelerating, rather than decelerating as had been expected, introduced dark energy as a central component of modern cosmological models. Dark energy is now estimated to constitute approximately 68 percent of the total energy density of the universe, yet its nature remains one of the foremost unsolved problems in physics.

The discovery prompted a shift in cosmological research, leading to the development of the Lambda-CDM model as the standard framework for understanding the large-scale structure and evolution of the universe. It also stimulated new lines of inquiry in theoretical physics, including investigations into whether the cosmological constant first proposed by Albert Einstein — and later abandoned by him — might in fact be a real property of spacetime.

Riess's more recent work on the Hubble tension has the potential to be equally consequential. If the discrepancy between local and early-universe measurements of the Hubble constant is confirmed to reflect new physics rather than systematic measurement errors, it could necessitate revisions to the standard cosmological model — a development that would rank among the most significant in twenty-first century physics.

Through his work at Johns Hopkins University and the Space Telescope Science Institute, Riess has mentored a new generation of observational cosmologists and has helped establish the field of precision cosmology, in which increasingly accurate measurements are used to test and constrain cosmological models. His ongoing research with data from the Hubble Space Telescope and the James Webb Space Telescope continues to push the boundaries of what is known about the expansion history of the universe.