Anderson’s considerations on the flow of superfluid helium: Some offshoots

The aim of this review, based on Anderson's ideas on phase slippage in superfluid helium, is to convey a physical meaning to the superfluid order parameter and its phase. This embraces an understanding of the superfluid order parameter phase and the associated processes that involve phase slip, the motion of vortices, critical velocities, Josephson effects, and phase slip associated with flow through small apertures. The review proceeds from a historical overview to a description of how the hydrodynamics of superfluid helium evolves from large to small scale, ultimately breaking down at close distance revealing the perplexingly elusive quantum properties of these fluids.