Two scientists have been awarded this year’s Nobel Prize in physics for their contributions to experiments showing neutrinos can change identity. Their detection of neutrino oscillations, which allow them to change "flavor," prove that neutrinos have mass, a discovery that the Nobel Prize committee said in a press release “has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe.”

Behind photons, neutrinos are the most abundant particles in the universe. Many are the result of reactions between cosmic radiation and the Earth’s atmosphere, while others are created by nuclear reactions inside the sun. It was long believed that neutrinos were massless, but the groundbreaking discoveries made by Takaaki Kajita of the University of Tokyo and Arthur B. McDonald of Queen’s University, Kingston, Canada, show these particles can change identities and therefore must have mass. 

In the late 1990s Kajita discovered that neutrinos from the atmosphere switched from one identity to another on their way to the Super-Kamiokande detector in Japan. Around the same time, the research group led by McDonald discovered that neutrinos from the sun weren’t disappearing on their trip to Earth, but instead changing identities. 

For decades physicists had been baffled when their theoretical calculations of the number of neutrons came out up to two-thirds higher than their physical measurements on Earth. These two experiments show that the neutrinos haven’t gone anywhere, they’ve just assumed a different form; as a result of these findings, neutrinos are now thought to come in three "flavors." The discoveries also challenge the Standard Model, a popular particle physics theory of the fundamental constituents of the universe that relies on the assumption that neutrinos are massless. 

Intense efforts continue to be made around the world to capture neutrinos and study their properties. Physicists predict any new discoveries could have a huge impact on our understanding of the makeup, history, and future of the universe.