Francis Halzen, a physics professor at the University of Wisconsin–Madison, has been awarded the 2026 Nobel Prize in Physics for his leadership of IceCube, the giant neutrino observatory buried in Antarctic ice. In remarks to reporters by phone early Tuesday morning, Halzen said the project that earned him the honor started as a partnership between his university and the University of California, Berkeley, according to UC Berkeley.
Halzen said he hoped the prize would draw attention to the wider collaboration behind the work and to the people who made decisive contributions to it over the years. He specifically noted that the effort began as a joint undertaking between Wisconsin and Berkeley.
That early partnership, known as AMANDA — short for Antarctic Muon And Neutrino Detector Array — grew over decades into the IceCube Neutrino Observatory. In 2013, the experiment confirmed the existence of high-energy neutrinos carrying roughly a million times the energy of neutrinos produced by the sun, UC Berkeley reports.
Why it matters
Neutrinos are elementary particles that rarely interact with anything, which makes them extraordinarily difficult to catch. IceCube solved the detection problem with sheer scale: its instruments are embedded throughout a cubic kilometer of South Pole ice, giving it enough volume to register the rare high-energy particles passing through.
The payoff, according to UC Berkeley, is a new understanding of the cosmos. Scientists now know that high-energy neutrinos arrive constantly from every direction. What remains unknown is where they originate and how they are produced — questions the observatory was built to help answer.
The prize also highlights a long-running academic partnership. Berkeley's role was not incidental; the collaboration traces back to conversations in the 1980s between Halzen and the late Berkeley physics professor P. Buford Price, who was then studying cosmic rays.
A theorist and an original thinker
Cosmic rays share a puzzle with neutrinos: at the very highest energies, their sources are unknown. Charged particles like cosmic rays are readily deflected by magnetic fields in space, which makes tracing them back to their origin difficult. Neutrinos, by contrast, travel in straight lines, so they can serve as a stand-in that points scientists toward the sources of cosmic rays.
Price was drawn to that possibility, and to the novelty of the detection scheme itself. Steven Barwick, now a physics professor at UC Irvine and at the time a graduate student and later a postdoctoral fellow in Price's lab, described Price as an original thinker who enjoyed pursuing new particles and new detector designs. Barwick said the match with Halzen worked because both men looked forward rather than back, calling them kindred spirits.
Spencer Klein, a Berkeley research physicist and senior scientist at Berkeley Lab who now leads the two local IceCube contingents, said Price's group was among the first to treat an ice-based detector as a serious proposition.
Barwick also acknowledged a simpler motivation: much of the team did not know what they would find, and that uncertainty was part of the appeal.
The concept was to place cameras in the continent's solid ice and watch for blue light. When a neutrino strikes another atom, the collision produces charged particles — often muons, which are essentially heavy electrons — moving faster through the ice than light does there. That produces Cherenkov radiation, which appears blue.
Drilling into the unknown
Soon after Halzen and Price began working together, members of Price's lab traveled to the South Pole on a previously scheduled trip to install a cosmic ray detector. They used the opportunity to bore holes in the ice and test whether it was clear enough to carry light without scattering.
The results were mixed. At the depths they examined, light could travel long distances, but bubbles in the ice — similar to those in a refrigerator ice tray — scattered it. The theory held that at sufficient depth the pressure would squeeze those bubbles out entirely. Tests in Greenland in 1991 confirmed it: photomultipliers placed in the ice picked up Cherenkov radiation from muons, though those muons had been created in the upper atmosphere by cosmic rays rather than by neutrinos from space.
Barwick said the Greenland tests and the first Antarctic tests fell short by some measures, but they established that the ice was highly transparent. The team knew the bubbles had to vanish at some depth, but did not know exactly where.
That depth turned out to be about 1.4 kilometers below the surface. There, scattering was low enough that researchers could trace a straight line from the detected light back to the muon, then to the neutrino, and finally to its source in the sky. According to Klein, Price's team went on to become pioneers of AMANDA, which demonstrated that a neutrino detector at the South Pole was genuinely feasible.
Proving the concept — and paying for it
Feasibility was only part of the battle. Halzen still needed backing and money. In a series of essays about AMANDA written in 2002, he recalled that despite the proof of concept, many people doubted the team would detect anything in ice at all, and that clear ocean or lake water was widely considered the better option.
Halzen wrote that persuading funders of the idea's soundness was difficult, noting that he was a theorist with no construction experience and that his early collaborators, while talented, were junior physicists at Berkeley. He credited the National Science Foundation with giving the group the benefit of the doubt, and said that within a few years the effort had grown to include eight other universities and three research laboratories across Belgium, Germany, Sweden and the United States.
AMANDA itself took the form of a cylindrical array: 19 separate strings carrying 677 detectors, mounted below the ice.
Halzen's remarks to the press reflected that history. He told reporters he wanted the award to recognize the large collaboration behind IceCube and the individuals whose contributions proved decisive over time, and he pointed to the project's origins as a Wisconsin–Berkeley effort.
The Nobel citation places Halzen among the researchers honored for work on the detection of cosmic neutrinos, a field that moved from theoretical proposal to confirmed observation over roughly three decades. The instrument that made the confirmation possible remains in operation at the South Pole, and the questions it was built to pursue — the origins and production mechanisms of the highest-energy neutrinos — are still open.
Watch for the next round of IceCube results, and for how the collaboration's growing network of partner institutions positions itself to chase those unanswered questions.
