The recent excitement in cosmology has been due to the emergence of a precision description of the present Universe and its recent past, with the standard model of cosmology able to accurately reproduce a wide range of sensitive observations. The ambitions of this effort are to determine the material composition of the present Universe, to establish the basic properties of perturbations in the Universe, and to verify that standard physical laws can be applied on a Universal scale. All of these now appear to be well in hand, as we have described in the earlier parts of this book. In particular, the successful theoretical reproduction of the observed cosmic microwave anisotropies is a tour de force of general relativity, particle interactions, and detailed modelling of the Universe's composition, that leaves little room for doubt that the fundamentals of cosmology are in place and secure.

Our book has also followed a broader ambition – to use that knowledge to tell us about the very early Universe and about the nature of fundamental physical laws. According to standard belief, almost every quantity measured in the present Universe has its origin in the Universe's earliest stages, when the primordial perturbations were created, perhaps by inflation, and when various as-yet uncertain particle physics processes established the densities of baryons, of dark matter, and perhaps also dark energy.