Neutrinos may pull their own weight in the universe



How many neutrinos are enough? The answer depends on what you need them for. If you want to find them and measure their energy, preferably in a proton decay detector, 1017 must go through the detector to yield just a few records of the particles' passing. But according to a study by physicists at a NASA laboratory, if you're interested in calculating a neutrino's rest mass, the dozen or so the detector catches are sufficient and could help provide an explanation for the “missing mass” that may fill most of the Universe.