The 2015 Nobel Prize in physics was announced Tuesday in Stockholm.

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WHO WON THE PHYSICS NOBEL?

Japanese physicist Takaaki Kajita, 56, director of the Institute for Cosmic Ray Research and professor at the University of Tokyo; and Canadian physicist Arthur McDonald, 72, of Queen's University, Ontario, Canada.

FOR WHAT?

Kajita and McDonald were cited for discovering neutrino oscillation, the process by which the subatomic particles switch between two identities, or forms. This insight proved that neutrinos, the second-most numerous particles in the universe after photons, must have mass.

SIGNIFICANCE

The Nobel committee said their discovery "has changed our understanding of the innermost workings of matter and can prove crucial to our view of the universe."