Neutrinos are very peculiar particles. Sometimes called “ghost particles”, they pass through our bodies every second, yet we cannot see or feel them. They come from the cosmos, as they are produced inside stars, during violent cosmic explosions, and around some of the most extreme objects in the universe, such as neutron stars. Somehow, they reach us after travelling across the universe for years. They can travel across billions of light-years almost undisturbed because they barely interact with matter. This offers an insight into just how strange these particles can be.
On October 6th, the Nobel Prize in Physics was announced, recognising physicist Francis Halzen for helping turn these ghost particles into a powerful and valuable way of understanding the cosmos. Halzen is a Belgian-American physicist at the University of Wisconsin–Madison, and has been awarded the 2026 Nobel Prize for his decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin.
This year, the award carries an unusual distinction: Francis Halzen is the first person since 1992 to receive the prize as its sole laureate. French physicist Georges Charpak was the last individual winner, recognised in 1992 for the invention and development of particle detectors. Since then, the Physics Nobel Prize has always been shared by two or three scientists.
But what makes Halzen’s work truly remarkable is that it has helped establish an entirely new way of observing the universe.
Nature and Neutrinos
The Standard Model is like a chart of the different particles that make up our universe. The smallest units of matter, atoms, are not fundamental, as was believed in ancient times. Instead, they are made of protons, neutrons, and electrons. Protons and neutrons are themselves made of smaller particles called quarks, while electrons are fundamental particles. Both quarks and electrons can be found in this classification. Another kind of fundamental particle is the photon, which makes up light, and there are, among others, neutrinos too.
Neutrinos, then, are elementary particles, and what makes them stand out is that they have no electric charge and an extremely small mass. They interact with matter through the weak nuclear force, one of the four fundamental forces of nature alongside electromagnetism, gravity, and the strong nuclear force. This means that they can pass through enormous quantities of matter without being absorbed or deflected, making them extremely difficult to detect, but also incredibly valuable.
In contrast to light, which can be absorbed or scattered as it travels through space, neutrinos can escape from extraordinarily dense environments and travel very long distances while preserving information about where they originated. Therefore, there is a paradox here: the property that makes them so scientifically useful is the same property that makes them so difficult to observe.
An Antarctic Ice Telescope
Halzen’s solution to the detection problem was to build a telescope in the Antarctic ice. The IceCube Neutrino Observatory does not look like a conventional telescope; there are no large mirrors pointing towards the sky. Instead, more than 5,000 light-sensitive detectors are distributed throughout approximately one cubic kilometre of Antarctic ice, between about 1.5 and 2.5km below the surface.
This idea dates back to 1988, when Halzen proposed using the transparent ice of Antarctica as a giant neutrino detector. The idea is based on the fact that when a high-energy neutrino interacts with an atom in the ice, it can produce a charged particle, which moves through the ice while emitting a faint flash of blue light known as Cherenkov radiation. These flashes are then detected by IceCube.
After collecting this data and studying the timing and pattern of the light, scientists can reconstruct the energy of the charged particle and obtain information about the neutrino that produced it. IceCube was constructed over several years, and its construction presented enormous challenges. The result, however, is one of the most unusual scientific instruments ever built: a particle detector the size of a mountain, hidden beneath the South Pole.
Seeing What Is Invisible
What makes IceCube memorable becomes clearer when we consider the presence of neutrinos. The universe contains objects capable of accelerating particles to enormous energies: supernova explosions, galaxies, and environments near supermassive black holes, among others. Neutrinos can carry information about these environments across vast distances.
An astronomical event can now be observed through light, gravitational waves, and neutrinos, each offering a different point of view. We are approaching a new era in modern astronomy: the multi-messenger era, where we start asking what the universe is doing, instead of simply what it looks like.
Even better news is that IceCube is not the only neutrino detector. The idea has been expanded into the depths of the Mediterranean with another neutrino telescope called KM3NeT. Future observatories could allow scientists to identify more cosmic neutrino sources and better understand how nature accelerates particles to energies far beyond what can be achieved on Earth.
Looking Downwards
A very interesting thing about this year’s award is the fact that Halzen’s work involves looking in a direction that astronomers often ignore. To observe the universe, we tend to look upwards, towards the cosmos, but IceCube does the opposite; it looks downwards.
Deep beneath the Antarctic surface, scientists are waiting for neutrinos that have crossed the Earth itself to leave a tiny flash of light in the ice. The most amazing thing is that this flash might have started its journey towards us billions of years ago.
The Nobel Prize in Physics 2026 recognises, then, more than the discovery of a particle signal; it recognises a change in how humanity observes the universe. Francis Halzen’s work demonstrates that sometimes the most important information about the cosmos is not carried by the light we can see, but by particles that almost never interact with anything at all.
From the darkness beneath the South Pole, a tiny flash of light has given us another way to see the universe.
