Professor Phillip Peebles FRS
P. James Peebles’s wide-ranging contributions to physical cosmology have established him as the leading exponent of this subject in his generation. In the early 1960s, he began to investigate galaxy formation and helium synthesis on the hypothesis that the Universe originated as a hot dense ‘primordial fireball’. Had it not been for this prior theoretical work, the cosmological significance of Arno Penzias and Robert Wilson’s serendipitous detection of ‘excess antenna temperature at 4080 megahertz’ would have been less readily appreciated. He has calculated in detail how various types of initial inhomogeneity may amplify (or decay) in an expanding universe, with reference to galaxy formation and the possible detectability of anisotropies in the background radiation. He has also investigated the detectability of ‘young’ galaxies, and offered compelling arguments for ‘missing mass’ in galactic halos and clusters.