3The Very Early Universe
For much of the early 20th century, cosmology barely existed as a scientific discipline. For instance, what we now recognise as distant galaxies very much like our own were thought to be unusual objects, nebulae, contained within our own Milky Way. In the light of our present knowledge, the progress of modern cosmology can be regarded as one of the great scientific endeavours of the 20th century, and as we reach the millennium the standard model of the Big Bang theory, described in Essay 1, is so well established that it is almost impossible to find a cosmologist willing to take issue with it. The successful predictions of the expansion of the Universe, of the cosmic microwave background radiation, of the light element abundances (the proportions of e.g. hydrogen, deuterium and helium present in the Universe) and of the age of the Universe are dramatic indeed.