sciencehabit writes from a report via Science Magazine: You can't weigh the universe's smallest particles on a bathroom scale. But in a clever new experiment, physicists have found one such particle -- the proton -- is lighter than previously thought. The researchers found the mass to be 1.007276466583 atomic mass units. That's roughly 30 billionths of a percent lower than the average value from past experiments -- a seemingly tiny difference that is actually significant by three standard deviations. The result both creates and clears up mysteries, and could help explain the universe as we know it. The findings have been published in the journal Physical Review Letters.