They abruptly lost their bit-player status last week, when a coalition of 120 physicists at 23 institutions in Japan and the United States announced that at least one of the three known kinds of neutrinos seems to have a smidgen of mass. Suddenly, neutrinos may be headliners of the cosmic show. The standard model of physics, a summary assembled by scientists to keep track of what they know, has always assigned neutrinos zero mass. The shy neutrino, it turns out, apparently has been hiding its talent for gravity. Yet there are so many neutrinos.
Trillions pass through every person every second.
Their mass would add up, big time, and be a crucial factor in controlling events spanning intergalactic distances. Scientists could see, from the behaviors of galaxies, that the universe is permeated by more gravity than could be provided by visible matter. Most have been flying around since the big bang, unaltered, although many nuclear reactions, and exploding stars, spew them too. At Super-Kamiokande, the occasional twinklings of the rare neutrinos that crash tell a strange tale. Those flying from above the Japanese detector are curiously too abundant, compared with those emerging from below, after a trip through the Earth's core.