Liquid Helium

Abstract

The phenomenon of superfluidity, like that of superconductivity occupies a unique position in the pattern of our known physical world. While at first there was a tendency to regard the unusual effects which were discovered as a limiting aspect of the properties of aggregate matter at very low temperatures, it is now quite clear that they have a more profound significance. The fact that these highly ordered states should make their appearance at temperatures which are two or three orders of magnitude smaller than the condensation of gases into the liquid and solid states may be nothing more than an accident due to the particular physical conditions obtaining on the surface of the earth. It is not at all impossible that in the universe as a whole the aggregation of matter may proceed more generally according to a pattern in which ordering of velocities takes precedence over ordering of positions. Thus, when discussing the behaviour of liquid helium, it is well to remember that the phenomena discovered so far may represent only a very limited aspect of a new pattern of assemblies of interacting particles. The peculiar analogy between superconductivity, an aggregation of charged light particles, obeying Fermi-Dirac statistics, and liquid helium, an assembly of uncharged atoms, following Bose-Einstein statistics, seems to emphasize the fundamental nature of the new state. The fact that these two rather dissimilar assemblies should follow the same pattern indicates that the pattern itself must be remarkably general.