A scientific tug-of-war is underway over the size of the proton. Scientists can’t agree on how big the subatomic particle is, but a new measurement has just issued a forceful yank in favor of a smaller proton.
By studying how electrons scatter off of protons, scientists with the PRad experiment at Jefferson Laboratory in Newport News, Va., sized up the proton’s radius at a measly 0.83 femtometers, or millionths of a billionth of a meter. That’s about 5 percent smaller than the currently accepted radius, about 0.88 femtometers.