A phenomenon occurring in a macroscopic system consisting of a large number of bosons at a sufficiently low temperature, in which a significant fraction of the particles occupy a single quantum state of lowest energy (the ground state). Bose–Einstein condensation can only take place for bosons whose total number is conserved in collisions. Because of the Pauli exclusion principle, it is impossible for two or more fermions to occupy the same quantum state, and so there is no analogous condensation phenomenon for such particles. Bose–Einstein condensation is of fundamental importance in explaining the phenomenon of superfluidity. At very low temperatures (around 2 × 10−7 K) a Bose–Einstein condensate can form, in which several thousand atoms become a single entity (a superatom). This effect has been observed with atoms of rubidium, lithium, and other atomic systems at extremely low temperatures. The effect is named after the Indian physicist Satyendra Nath Bose (1894–1974) and Albert Einstein. See also low-temperature physics (Feature).