Francis Halzen reflected on the uncertainty surrounding an idea first put forward decades ago when he addressed a news conference. “I have to emphasise how lucky I was. Because when we started this project, everybody realised this was maybe a good idea, but very few thought it would work, including myself.”
On 6 October 2026, the Royal Swedish Academy of Sciences awarded Halzen the 2026 Nobel Prize in Physics for “decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin”.
Halzen, who was born in 1944 in Tienen, Belgium, is now a US citizen and a Vilas Research Professor and Gregory Breit Professor at the University of Wisconsin–Madison.
His central proposal was simple in outline and difficult in practice. In 1988, Halzen set out his vision for detecting neutrinos at the South Pole, realising that the ice there could be used to track the particles.
Neutrinos rarely interact with material, allowing them to pass through dense regions that light cannot easily penetrate. They also carry no electric charge, so magnetic fields do not bend their paths through space.
Halzen proposed and demonstrated that ice could serve as a detection medium for high-energy astrophysical neutrinos. When a neutrino collides with an atomic nucleus, it produces a flash of light. Sensors can track that flash in clear glacial ice.
IceCube was built at the South Pole as a cubic kilometre of Antarctic ice filled with thousands of light sensors. The sensors sit on long cables drilled and frozen into a 1km cubic block of ice. The site offers ice free from various forms of interference, as well as geological stability without earthquakes.
The observatory was finished in 2011. In 2013, it detected high-energy astrophysical neutrinos, though the sources of those particles were unknown at the time.
IceCube later reported evidence of neutrino emission from the galaxies TXS 0506+056 and NGC 1068 (Messier 77). In 2023, it announced that it had observed neutrinos from the Milky Way.
The IceCube Upgrade was installed in 2025–2026 to lower the observatory’s energy threshold and improve calibration of the ice.
The project is an international collaboration of 450 scientists from 58 institutions in 14 countries. Erin O'Sullivan is the collaboration’s spokesperson.
Mark Pearce, chair of the Nobel Committee for Physics, said Halzen had led an international team and that his persistence and scientific vision had helped establish a new kind of astronomy. Ekaterina Zaharieva, Commissioner for Startups, Research and Innovation, said Halzen’s work had opened a new window onto the Universe.
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