We have now pushed our model of the history of our Universe back just about as far as we could hope to go: the Universe had a beginning, and that beginning was the source of all that happened afterwards – all matter, all stars, all galaxies, even life itself. Big Bang cosmology has placed modern physics in the remarkable position of being able in principle to trace back to the beginning every aspect of the world we live in, to say “This is where X came from, and this is how Y started”.

1. ▷ The background image on this page is a plot of the spatial distribution of galaxies in a thin wedge of space centered on our position, from the CfA Redshift Survey. Measured in 1985, this distribution gave astronomers their first indication that galaxies were grouped into chains as well as clumps. The human-like pattern (horizontal in this view, with the legs to the left) became a celebrity in its own right. Data from M Geller and J Huchra, image copyright South African Observatory (sao).