What a difference is made by one‐half quantum unit of spin. Atoms with integer spins—bosons—can collapse into a common ground state when sufficiently cold; the result is a collective state known as a Bose–Einstein condensate (BEC). But atoms with half‐integer spins—fermions—are excluded from occupying the same quantum states. The lowest‐energy configuration they can reach is to fill all levels up to the Fermi energy—the highest level that would be occupied at absolute zero.