It could be said that the discovery and subsequent exploration of the cosmic microwave background radiation marked a transition from cosmology as a branch of astronomy that was largely a philosophical endeavour to cosmology as an astrophysical discipline that is now a fully fledged branch of physics. The CMB established a secure physical framework within which we could undertake sophisticated experiments that would define the parameters of that framework with ever greater precision. As understanding has grown, more and more of traditional astronomy has been embraced to provide evidence in support of this new paradigm: we have garnered evidence from the study of stars, such as supernovae, of galaxies and their velocity fields, and from observations of galaxy clusters and clustering. These studies have involved ground-based and space-based experiments at all wavelengths from radio to gamma-rays.

‘Precision Cosmology’ was born and we now have the recognised disciplines of ‘astro-particle physics’, ‘astro-statistics’ and ‘numerical cosmology’, to name but a few.

Fifty years on from the discovery of the CMB a number of issues have been clarified, but many more remain. Among the numerous areas of active research in cosmology today, there are three which have particular bearing on the first half million years: dark matter, dark energy and gravitational waves.