Current understanding of the state of the universe.
It is based on the finding that all galaxies are moving away from each other. Application of general relativity to cosmology, along with the detection of redshifted light coming from galaxies outside the Milky Way Galaxy, led to the realization in the 1920s that all galaxies are receding (see Edwin Hubble ). It is unknown whether the universe will expand indefinitely (open universe) or eventually collapse (closed universe) into an extremely dense, congested state, as it began, according to the big-bang model. See also Friedmann universe .