Nuclear physicists have found that the proton is four percent smaller than what was originally believed, according to a study published in Science, reports Davide Castelvecchi for Nature. In 2010 researchers studying a type of lab-created muonic hydrogen found the protons were 4% smaller than previously estimated. Some thought the lab-created hydrogen had heavier protons due to a previously undiscovered type of physics, but this study, which found similar results in regular hydrogen, suggests that the earlier measurements were incorrect and no physics needs to be rewritten.
Why it matters: This backs up a previous finding that "has made physicists doubt their most precise measurements, and even their most cherished theories," writes Castelvecchi.
But, but, but: The physicists are "not quite ready to claim that the puzzle has been solved," Nature reports. It's possible past measurements with large protons were correct, so they study authors are waiting for results from other experiments. Science News writes that different techniques are coming up with different results.