Physics Pioneer Pierre Sokolsky awarded the 2025 Yodh Prize

July 23, 2025
Above: Pierre Sokolsky

To many, the (literally) rarefied air of the field of ultra high energy cosmic ray physics can prove elusive. And yet, these particles from outer space that travel across the universe at nearly the speed of light are in fact key to our understanding space, including the makeup of the galaxies and the universe.

Particle astrophysicists know this, and every other year the Commission on Astroparticle Physics of the International Union of Pure and Applied Physics (IUPAP) gather at the International Cosmic Ray Conference (ICRC) to recognize one of their peers with the Yodh Prize.

This year, Pierre Sokolsky, distinguished professor of physics (emeritus) at the University of Utah received the award at the the conference being held in Geneva, Switzerland.

Atmospheric fluorescence technique

The prize, which recognizes a scientist whose research career has had a major impact on the understanding of cosmic rays, was well-deserved by Sokolsky who played an instrumental role in pioneering the development of the atmospheric fluorescence technique as a method for exploring the highest energy cosmic rays. His work in understanding and verifying the extraordinary 1991 “Oh-My-God” event, observed by Utah's Telescope Array and which weighed in at 3.2x10^20 eV was pivotal.

Illustration of the Oh-my-God particle.

"Pierre’s deep understanding of cosmic ray physics, combined with his ability to communicate complex phenomena to newcomers, was invaluable to the development of the field," says John Matthews, a U colleague in the Department of Physics and Astronomy, program manager for the cosmic ray physics group and co-spokesperson of the Telescope Array project.

In fact, Sokosky's expertise, both theoretical and practical, was recognized when he was awarded the Panofsky Prize by the American Physical Society (APS) in 2008, with George Cassiday, for groundbreaking contributions to the fluorescence technique at Fly's Eye.

Named for its design, which mimicked the compound eye of an insect, the high resolution Fly's Eye was a cosmic ray observatory which used a large array of mirrors and photomultiplier tubes to detect the faint flashes of light produced when cosmic rays interact with the atmosphere. This technique, called air (or atmospheric) fluorescence—which Sokolsky helped develop, particularly in the construction of its monocular and stereo detectors—allowed scientists to study the highest energy cosmic rays. Their findings, which included the first evidence for the cosmic ray suppression and the Greisen-Zatsepin-Kuzmin (GZK) cut-off culminated, according to Matthews, in groundbreaking results that were published in Physical Review Letters in 2008.

"Pierre’s unwavering commitment to the field, his scientific acumen and his ability to foster international collaboration have made him one of the most influential figures in ultra high energy cosmic ray physics," says Matthews. "His work has significantly shaped the understanding of cosmic ray origins, and his leadership has been instrumental in producing critical results for the field."

Next phase of the Telescope Array

"This award adds to the long list of recognitions that members of our department have received for their pioneering research in cosmic ray physics," says Carsten Rott, chair of Department of Physics and Astronomy and the Jack W. Keuffel Memorial Chair. Rott, speaking from the ICRC conference where the ceremony honoring Sokolsky is taking place, continues:

"This award is well deserved for Pierre and comes at a critical time where we are trying to complete the construction of the next phase of the Telescope Array cosmic ray detector (TAx4) in Utah. The importance of the anticipated data to be obtained from the completed TAx4 project was also stressed multiple times during this conference."

Gaurang Bhaskar Yodh (1928-2019) was an Indian-American physicist and an expert in astroparticle physics and cosmic-ray physics. The prize is endowed by Gaurang and his wife Kanwal to the UC Irvine Foundation which sponsors the award.

The recipient is selected on behalf of the University of California Irvine Foundation, which sponsors the accolade. In addition to a cash prize, Sokolsky is invited to give a talk at UC Irvine's Department of Physics and Astronomy.

Sokolsky, who retired from the U in 2020 is also Dean Emeritus of the College of Science at the University of Utah. Born in France, he was educated at the University of Chicago and University of Illinois. He is a Fellow of the American Physical Society.

In addition to winning the Panofsky Prize he has been a Sloan Fellow (1977), recipient of a 2006 Utah Governor's Medal for Science and Technology  and was elected a Guggenheim Fellow (2020).

In 2004, he spearheaded the U’s $17 million Telescope Array Project located just west of Delta, Utah, to study ultra-high-energy cosmic rays in collaboration with scientists from the University of Tokyo Institute for Cosmic Ray Research and several other Japanese universities as well as team members from South Korea, Russia, and Belgium.

Pierre Sokolsky also launched a comprehensive astronomy research program at the U, including undergraduate and graduate degrees in astronomy.

by David Pace