October 6, 2015 - 15:43 AMT
Nobel Prize in Physics celebrates work on neutrinos

Takaaki Kajita of the University of Tokyo and Arthur B. McDonald of Queen’s University in Canada were awarded the Nobel Prize in Physics on Tuesday, October 6, for discovering that the ubiquitous but elusive subatomic particles known as neutrinos have mass, the New York Times reports.

Neutrinos are the second most abundant subatomic particles in the universe, after photons, which carry light. Their existence was predicted in 1930, but for decades they remained some of the most enigmatic elements of astrophysics.

The ghostly neutrino — it means “small neutral one” in Italian — carries no electric charge and is so light that it had been assumed for many years to have no mass at all. The scientists showed that neutrinos, which are found in three “flavors,” could oscillate from one flavor to another — changing identities like a spy on the run, as they traveled through the atmosphere or through space from the sun — demonstrating that they do in fact have mass.

Dr. Kajita was part of a team of researchers who in 1998 discovered that neutrinos from the atmosphere switched between two identities on their way to the Super-Kamiokande detector, nearly two-thirds of a mile below the earth’s surface.

In 1999, Dr. McDonald announced that neutrinos from the sun were not disappearing on their way to the earth. He and his colleagues had captured the neutrinos using a uniquely sensitive new detector 6,800 feet below ground, at the Sudbury Neutrino Observatory, which is part of Queen’s University in Kingston, Ontario.

The universe is swamped in neutrinos that are left over from the Big Bang, and many more are created in nuclear reactions on earth and in the thermonuclear reactions that power the sun.

Once thought to travel at the speed of light, they drift through the earth and our own bodies like moonlight through a window. Knowing that they can change identities — and that they have mass — has helped cosmologists understand how the universe has evolved and how the sun works, and it will perhaps help them improve their attempts to create fusion reactors on earth.