The DC Josephson effect is the flow of supercurrent across a weak link between two superconductors with different values of their order parameters, the phase. We formulate this notion for any kind of spontaneous continuous symmetry breaking. The quantity that flows between the two systems is the zero-wavenumber Noether current associated with the broken symmetry. The AC Josephson effect is the oscillation of current due to the energy difference between the two systems caused by an imposed

more »

... tric chemical potential of Noether charge. As an example of novel physics, a Josephson effect is predicted between two crystalline solids, potentially measurable as a force periodic in the separation distance.