Quantum cows - part 2

The 2026 Nobel Prize in Physics has been awarded to Francis Housen of the University of Wisconsin-Madison in the United States for decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin.

Francis Housen laid the foundation for an entirely new type of astronomy.

His idea was to use glacial ice at the South Pole to capture hard-to-detect particles called neutrinos.

The result was the IceCube Neutrino Observatory, which can track neutrinos that come to us from the distant parts of the universe.

The neutrino is the hardest-to-detect particle in the universe that definitely exists.

It's sometimes called a ghost particle.

Neutrinos have no electric charge and almost no mass.

In general, they pass unnoticed through matter.

It's very rare for a neutrino to collide with an atomic nucleus so that it can be detected.

Every second, 65 billion neutrinos from the Sun flow through your little fingernail without you noticing.

Neutrinos also travel from other regions of space, carrying clues to some of the mysteries of the universe.

Researchers that succeed in capturing these rarer cosmic neutrinos can then extract information about the extreme environments in the universe that they came from.

In the 1980s, Francis Housen had realized that Antarctic ice could be ideal for capturing enough of these ghostly neutrinos.

In 1992, a group of researchers and engineers made the first attempts to lower light sensors into the glacier at the South Pole.

20 years later, the IceCube Neutrino Telescope registered neutrinos with properties that convinced researchers that they originated in distant parts of space.

Cosmic rays travel across the universe and hit the Earth.

Typically, these particles are protons, which are naked atomic nuclei of hydrogen.

Protons from space can sometimes reach us with an astounding amount of energy, far more than it's possible to give them in a particle accelerator on Earth.

Nobody knows the origin of cosmic rays.

Because the processes that can accelerate protons to high energies also give rise to neutrinos with high energies, neutrinos could provide important clues about what is causing cosmic rays.

Neutrinos that carry huge amounts of energy are easy to distinguish from the lower energy neutrinos that come from decaying radioactive elements, or from the sun, or are generated when cosmic rays hit the atmosphere.

High-energy neutrinos that don't come from nearby must come from somewhere far, far away, perhaps from violent processes in regions where stars have exploded or from distant active galaxies.

Around 1960, physicists had suggested that water could be a good material for capturing neutrinos from space.

On the rare occasions that a neutrino collides with an atomic nucleus, a charged particle is produced.

This travels in the same direction as the original neutrino and emits a blue light.