Bose–Einstein distribution, a formula describing the distribution over energy levels of identical particles with zero or integer spin, on condition that the interaction of the particles in the system is weak and can be neglected. In statistical equilibrium the mean number ni of such particles in the state with energy Εi (above the degeneracy temperature) is given by the Bose–Einstein distribution: ni=1/(e(Εi-μ)/kT-1), where i is the set of quantum numbers characterising the state of the particle, μ — the chemical potential.