ABSTRACT
We study a system of interacting bosons at very low temperatures. We assume that the density of the system is such that it remains liquid at absolute zero, a condition which is, in fact, satisfied only by 4He. For helium, the forces are relatively weak, while, because of its low mass, the zero-point oscillations of the individual atoms are large. As a result, as London (1938) has shown, helium may be expected to remain a liquid down to the lowest temperatures. (Hydrogen solidifies because of the much stronger inter-atomic forces, while the heavier inert gases solidify at low temperatures because their zero-point oscillations possess lower amplitude.)
