A measurement of the size of the proton, obtained using spectroscopy of an exotic atomic system, yields a result of unprecedented accuracy — but in disagreement with values obtained by previous methods.

K+ channels can convert between conductive and non-conductive forms through mechanisms that range from flicker transitions (which occur in microseconds) to C-type inactivation (which occurs on millisecond to second timescales). Here, the crystal structures are presented of the potassium channel KcsA in an open-inactivated conformation and 'trapped' in several partially open conformations. The structures indicate a molecular basis for C-type inactivation in K+ channels.

Here, a technically challenging spectroscopic experiment is described: the measurement of the muonic Lamb shift. The results lead to a new determination of the charge radius of the proton. The new value is 5.0 standard deviations smaller than the previous world average, a large discrepancy that remains unexplained. Possible implications of the new finding are that the value of the Rydberg constant will need to be revised, or that the validity of quantum electrodynamics theory is called into question.