The discrepancy between the measured Lamb shift in muonic hydrogen and expectations from electron-proton scattering and hydrogen spectroscopy has become known as the proton radius puzzle, whose most "mundane" resolution requires a ∼5σ shift in the value of the Rydberg constant. I review the status and outlook for experimental spectroscopic and scattering measurements focused on resolving the puzzle. I describe recent theoretical developments motivated by the proton radius puzzle, and broader implications for particle physics.

Argonne Physics Division Colloquium Schedule