Last week a group of physicists at York University published a new precision measurement of the proton charge radius in the journal Science.

In 2010 physicists at the Max Planck Institute reported the most precise measurement of the proton charge radius to date. They obtained this result by studying energy levels in a type of “heavy” hydrogen called muonic hydrogen. Muonic hydrogen is just regular hydrogen with it’s electron replaced by its 207-times-heavier sibling, the muon.

The puzzle was that their result, and a subsequent measurement, showed that the proton’s charge radius is about 4% smaller than the accepted average (based on dozens of previous measurements). The discrepancy resulted in years of speculation of new physics.

There’s still a lot of physical phenomena we don’t understand fully, or at all. Physicists study discrepancies to hopefully find clues about new physics. However, since this new result agrees with the smaller measurement, it’s likely that the old value for the proton radius is simply incorrect – not that there’s new physics.

The new result is cool for two reasons: one, the proton has a new radius (0.833 femtometres). Two, my fiancé was one of the physicists who published this result! Congratulations to everyone in the Hessels lab – it was many years of hard work and dedication that has finally paid off.