Among the various competing cosmological models of the evolution of universe, the Big Bang theory is the most widely accepted model. According to this model, the universe started off from a very-very dense location of matter and gases, at extremely high temperatures. From this singularity, the universe started expanding in a big explosion, and hence the name big bang. All the celestial bodies, including planets, stars, constellations, galaxies, etc. were formed over the last 13-15 billion years of time (estimated age of universe). The expansion is continuing even today and it was postulated that all the galaxies are moving away from each other. The expansion of our universe has been confirmed by observations of Edwin Hubble. Further support for the big bang theory, in the form of cosmic background radiation, was detected in 1965.
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