Large proton halo sparks devilish row

IN CHRISTIAN art, a halo symbolises holiness. In particle physics, a ring of positive charge around the proton has become the focus of a devilish row.

The dispute concerns an attempt to square a recent suggestion that the radius of the proton is smaller than we thought with the theory of quantum electrodynamics (QED), which has successfully explained quantum phenomena since the 1940s.

A proton’s radius cannot be measured directly, but has to be deduced by measuring the energies of different electron “shells” in a hydrogen atom. Through QED, these energies combine with a model of how the proton’s…