Editing Superfluid helium-4 (section)

=== Comparison with helium-3 ===
Although the phenomenologies of the superfluid states of helium-4 and helium-3 are very similar, the microscopic details of the transitions are very different. Helium-4 atoms are bosons, and their superfluidity can be understood in terms of the [[Bose–Einstein statistics]] that they obey. Specifically, the superfluidity of helium-4 can be regarded as a consequence of Bose–Einstein condensation in an interacting system. On the other hand, helium-3 atoms are fermions, and the superfluid transition in this system is described by a generalization of the [[BCS theory]] of superconductivity. In it, [[Cooper pair]]ing takes place between atoms rather than [[electron]]s, and the attractive interaction between them is mediated by [[Spin (physics)|spin]] fluctuations rather than [[phonon]]s. (See [[fermion condensate]].) A unified description of superconductivity and superfluidity is possible in terms of [[spontaneous symmetry breaking|gauge symmetry breaking]].