Francis Halzen, a Belgian particle physicist at the University of Wisconsin-Madison, has been awarded the 2026 Nobel Prize in Physics for his decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin. The Royal Swedish Academy of Sciences announced the prize on Tuesday, recognizing work that has opened an entirely new window on the cosmos.
The idea that led to the prize took shape in 1988, when Halzen realized that the ice at the South Pole could be used to detect cosmic neutrinos. Two decades later, IceCube began operation. The detector comprises many light detectors embedded in a cubic kilometre of Antarctic ice. Occasionally a neutrino interacts with the ice, creating particles that generate light as they travel through the ice. By tracking these particles, Halzen and his colleagues can determine where in the sky the neutrino came from.
«Halzen had the idea together with a colleague in 1988 to use the ice at the South Pole as a medium to detect neutrinos,» said Mark Pearce, chair of the Nobel Committee for Physics and an astroparticle physicist at KTH Royal Institute of Technology in Stockholm. Pearce added that Halzen «has spearheaded an international collaboration of more than 450 people from 58 institutions in 14 countries around the world to realize this enormous neutrino detector.»
Speaking by telephone shortly after the announcement, Halzen said, «It was a great surprise and I didn't expect it. It's a great pleasure to hear about this prize.» He reflected on the long effort behind the discovery: «When I reflect on this moment, I have to say how lucky I am. This was an adventure where success was not guaranteed, but we overcame many challenges. It was a long journey. I want to emphasize again how lucky I was to take contributions from collaborators. It feels strange. I hope it reflects on the courageous people who joined me on this project. Many talented people joined me on this journey.»
Halzen also credited his university for providing the right environment for the project. «I was lucky to be in the right place when this idea came up,» he said. Asked what he planned to do for the rest of the day, he replied, «I'm working on a proposal. I hope this prize will help get it approved.»
Pearce explained why neutrinos hold such fascination for physicists. «The neutrino has such peculiar properties, the fact it interacts so infrequently in material, and in this case it's a way of bringing information about distant cosmic sources that we are unable to acquire in other ways,» he said.
Halzen was born in Belgium in 1944. He earned an MSc in physics from the University of Louvain in 1966 and a PhD from the same university in 1969. After a stint at the CERN particle-physics laboratory, he moved to the University of Wisconsin-Madison in 1972, where he became principal investigator on the AMANDA neutrino observatory in Antarctica and later the IceCube project. In 2013, Halzen and his IceCube colleagues received the Physics World Breakthrough of the Year award.
The prize is worth SEK 12 million, about $1.2 million, and will be awarded in Stockholm on 10 December. Halzen is the first sole winner of the Nobel Prize in Physics since Pierre-Gilles de Gennes in 1991. This is the fifth Nobel Prize related to neutrinos, underscoring the growing importance of the elusive particle in modern physics.
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