The Nobel Prize in physics is awarded for discovering that the universe’s most elusive particles have mass

Chasers of tiny particles.
Chasers of tiny particles.
Image: Reuters/Kyodo/McDonald
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If you close your fist right now, you will, for a brief moment, hold what won two scientists this year’s Nobel Prize in physics. The prize was given to Arthur McDonald of Queen’s University in Ontario and Takaaki Kajita of the University of Tokyo “for the discovery of neutrino oscillations, which shows that neutrinos have mass.”

Neutrinos are the second-most abundant particle in the universe after light particles (photons). Billions are passing through your body right now at the speed of light, because they very rarely interact with other particles. That is why, even though their existence was predicted by physicists in the 1930s, they weren’t detected until the 1950s.

For a long time, scientists thought that neutrinos were massless. However, as our understanding of the fundamental particles of the universe improved, scientists noticed that the number of neutrinos we were able to detect on Earth was only two-thirds of what the theories suggested should reach the planet from the sun.

Kajita and McDonald’s set out to find where the missing neutrinos were hidden. The only place they could do that was deep underground, where most radiation can be filtered out. Kajita used a detector in a zinc mine in Japan and McDonald used one in a nickel mine in Canada.

When combined, their research showed that these neutrinos were oscillating between ”flavors”—not in the sense of taste, but in how mathematical equations describe different kinds of neutrinos. These flavors explained the missing neutrinos, and, according to these complex calculations—which really only physicists can understand—such changes in flavor meant that neutrinos have mass.

The practical implication of this research was to raise questions about the Standard Model, which physicists consider the definitive list of fundamental particles and how they interact. Kajita and McDonald’s work forced physicists to question these long-held assumptions, and for that alone they deserve the highest accolade in their field.

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