Expanding universe. Computer artwork of galaxies (blue-yellow) in an expanding universe. A yellow glow (centre) represents the origin of the universe in the Big Bang, the initial expansion of the universe from an infinitely compact state 12-15 billion years ago. Matter formed and, around 100 million years after the Big Bang, condensed into the stars that formed the galaxies. On the largest scale, these galaxies are observed to be moving away from each other, rather than a central point. This is seen as the continuing general expansion of the universe. A common analogy is to imagine the universe and its galaxies as being contained on the surface of an expanding bubble.