The Universe grows old

Enormous stretches of time have elapsed since the Big Bang. The twilight of the first million years has been transformed into near complete darkness. The fossil radiation, a relic of the Big Bang, that was still dimly lighting the large cooling masses of gas, has diluted and shifted to the infrared, because the expansion of space goes on. This radiation soon becomes completely invisible. In the opaque night of the first billion years, the masses of gas become more and more patchy. This is because density fluctuations increased, and the aggregates of gas were more and more separated, first into superclusters, then clusters of galaxies, and finally into galaxies.

The ‘timeless night’ probably ends during the second billion years, because the quasars light up the central clusters of many galaxies. Their dazzling light hides the simultaneous appearance of many small bright dots that studded the galactic halos. The stars have just lit up, in the globular clusters and in the large central cluster of many galaxies.

The galaxies each evolve somewhat differently. They display a large diversity in sizes, and in angular momenta, which comes from the turbulence in the gas masses.