Being a characteristic quantity of an atom's or ion’s electronic state, the polarisability of atoms or ions with several electrons had been difficult to obtain to date because simple equations for it ...

It is easily shown that in the latter problem no divergencies occur. The calculation of the polarisability of the vacuum or of scattering of light by light, however, leads to divergent series.

Polarisability determines the force with which an inhomogeneous external electric field acts on the ions of an ion beam. However, it can be quite tricky to obtain accurate values for this force.

Strong interaction theory makes a precise prediction on the polarisability of pions – the degree to which their shape can be stretched.