‘Ghost particle’ coming into focus: Scientists put upper limit on mass of neutrinos

Every second, about 100 trillion neutrinos pass through your body. These ghostly particles are fundamental to our understanding of the universe. But they’re extremely small — so small that scientists once thought they had no mass at all. 

Neutrinos do indeed have mass, however, and physicists have now managed to put a new upper limit on it: 0.8 electronvolts, or eV. (Electronvolts are technically a measure of energy, but mass and energy are equivalent, as shown by Albert Einstein’s most famous equation, E=mc^2.)