The Royal Swedish Academy of Sciences has decided to award the 2026 Nobel Prize in Physics to Francis Halzen "for his decisive contributions to the IceCube neutrino observatory and the discovery of high-energy neutrinos of astrophysical origin."
Francis Halzen laid the foundation for an entirely new direction in astronomy, the Nobel Committee said in a statement.
His idea was to use the ice of the South Pole glaciers to trap particles called neutrinos. The result was the IceCube Neutrino Observatory, capable of tracking neutrinos originating from deep space.
Halzen played a pivotal role in the creation of the IceCube neutrino observatory, a one-cubic kilometer ice cube equipped with light sensors. With IceCube, scientists can detect neutrinos produced by extremely high-energy processes in the distant Universe.
Francis Halzen was born on March 23, 1944 in the Belgian city of Tienen. In 1969 he defended his doctorate at the Catholic University of Leuven (KU Leuven) in Belgium. He is a professor at the University of Wisconsin–Madison in the USA.
Neutrinos are particles that interact extremely weakly with matter, making them particularly difficult to detect. Very rarely, an individual neutrino interacts with an atomic nucleus, which allows them to be detected using appropriate instruments.
“Neutrinos are ghostly particles, they have virtually no mass, move at the speed of light and can cross the entire galaxy directly without ever colliding with anyone. That’s why it takes a huge detector to see them,” Oxford University professor Subir Sarkar explained in an interview with the BBC.
Scientists have long known that there are natural particle accelerators in space that eject particles with energies a million times greater than what can be achieved in laboratories on Earth. Much about these sources remains a mystery: what kind of sources are they, where are they located, and what are the main processes occurring in them?
The Earth is bombarded every second by cosmic rays, consisting of countless particles, protons and neutrons, accelerated by powerful electromagnetic fields to almost the speed of light. The movement of these rays is chaotic, and it is almost impossible to determine their exact source. But along the way, these particles collide with gas and dust in interstellar space.
Extremely high-energy neutrinos arise in the same environments as other types of particles. However, unlike other particles, neutrinos reach us without changing direction or losing energy, and as a result, they can provide information that is not available in any other way.
Francis Halzen first presented his concept of detecting neutrinos at the South Pole in 1988. When a neutrino collides with an atomic nucleus, it produces a flash of light that can be tracked using sensors embedded in transparent glacial ice.
The ice of the South Pole has many advantages, since it is free from various types of impurities, and the area itself is geologically stable and not prone to earthquakes. Halzen's idea soon gained support from other researchers, and just a few years later preliminary tests of sensors in ice were carried out.
Cosmic neutrinos with extremely high energies are very rare, so observing a sufficient number of collisions requires a huge volume of ice. IceCube occupies a volume of one cubic kilometer and its construction was completed in 2011. Soon, researchers discovered the first high-energy neutrinos, and a few years later they detected neutrinos that apparently originated far beyond our solar system.
“Francis Halzen led an international team of researchers and engineers who created a fantastic device. His tenacity and scientific vision paved the way for a new kind of astronomy,” says Mark Pearce, Chairman of the Nobel Committee on Physics.
The neutrino interactions that IceCube continuously records will provide researchers with new knowledge about the turbulent environments in which high-energy neutrinos can be produced, and may even reveal previously unknown cosmic phenomena.
The winners of the 2025 Nobel Prize in Physics are Briton John Clarke, American John M. Martinis and Frenchman Michel H. Devore.
They received the prize for their discovery of macroscopic quantum mechanical tunneling and energy quantization in an electrical circuit.
Since 1901, the Nobel Prize in Physics has been awarded 120 times, with 228 winners.
The youngest recipient of the prize in physics is Lawrence Bragg, who received the prize in 1915 at the age of 25. The oldest is 2018 laureate Arthur Ashkin, who received the prize at the age of 96.
Nobel Week traditionally takes place in Stockholm in early October. The Physics Prize is the second to be awarded.
On the first day, laureates in the field of medicine and physiology become known. This is followed by awards in the fields of physics, chemistry, literature, and at the end of the week the Nobel Peace Prize laureate is announced; it can be not only an individual, but also entire organizations.
This is the only prize that is awarded not by the Swedish, but by the Norwegian Academy of Sciences.
