The hypothesis, based on the evidence of the redshift, that the distance between the galaxies is continuously increasing. The original theory, which was proposed in 1929 by Edwin Hubble, assumes that the galaxies are flying apart as a consequence of the big bang with which the universe originated. Several variants have since been proposed. In 1998 it was discovered that the expansion of the universe is accelerating. See also Big-bang Theory (Feature); Hubble constant.