Reversible and irreversible evolution of a condensed bosonic gas

More than 70 years ago, Bose and Einstein proposed a provocative hypothesis—that at ultralow temperatures a novel state of matter should exist. They predicted this state could be attained by cooling an ordinary gas towards absolute zero. At a well-defined point in this process, a spontaneous transition should occur and change the state of matter from an unordered ensemble of individual particles into one collective entity. This single object, now devoid of its manyparticle character, ought to evolve as a collective matter wave.