Credit: Sonnet Malakaran George/Alamy An analysis of the jumps of a hydrogen atom’s electron has yielded a new, precise value for the Rydberg constant, a fundamental quantity in physics 1.

At the core of the “proton radius puzzle” is a four–standard deviation discrepancy between the proton root-mean-square charge radii (rp) determined from the regular hydrogen (H) and the muonic ...