Good fortune from a broken mirror

We know of four fundamental forces in nature: the electromagnetic, weak, strong, and gravitational interactions [1]. The interaction between electrons and nuclei in atoms is predominantly electromagnetic, but there are tiny effects from the weak force. The weak force only acts over a distance that is as short as 0.1% the diameter of a proton, and the size of its effects in an atom is many orders of magnitude less that of the electromagnetic force. As a result, the weak interaction can only be detected with very high-precision experiments. Now, Konstantin Tsigutkin and colleagues at the University of California, Berkeley, US, report in Physical Review Letters an experiment on ytterbium (Yb) in which they have observed the largest weak interaction effect in atoms to date [2]. It is 100 times larger than what has been seen in cesium (Cs), the atom with which the first [3] and, so far, most accurate measurements [4] of the weak force in atoms have been performed and which has established the experimental basis for almost all of the research in this field. The finding of such a large effect in Yb encourages the ongoing search for the weak interaction in other heavy atoms and provides in itself an opportunity to use tabletop atomic physics techniques as part of sensitive searches for new physics beyond the standard model.