one of two possible ways in which a collection of indistinguishable particles may occupy a set of available discrete energy states (energy state). The aggregation of particles in the same state, which is characteristic of particles obeying Bose-Einstein statistics, accounts for the cohesive streaming of laser light and the frictionless creeping of superfluid helium. The theory of this behaviour was developed (1924–25) by Albert Einstein (Einstein, Albert) and the Indian physicist Satyendra Nath Bose (Bose, Satyendra Nath), who recognized that a collection of identical and indistinguishable particles can be distributed in this way.

In contrast to Fermi-Dirac statistics, the Bose-Einstein statistics apply only to those particles not limited to single occupancy of the same state—that is, particles that do not obey the restriction known as the Pauli exclusion principle. Such particles are named bosons (boson), after the statistics that correctly describe their behaviour.