Olbers' paradox states that given the Universe is unbounded, governed by the standard laws of physics, and populated by light sources, the night sky should be ablaze with light. Obviously this is not so. However, the paradox does not lie in nature but in our understanding of physics. A Universe with a finite age, such as follows from big-bang theory, necessarily has galaxies of finite age. This means we can only see some of the galaxies in the Universe, which is the main reason why the night sky is dark. Just how dark can be calculated using the astrophysics of galaxies and stars and the dynamics of relativistic cosmology.
We know from the dynamics of individual galaxies and clusters of galaxies that the majority of matter that exerts gravitational forces is not detectable by conventional telescopes. This dark matter could have many forms, and candidates include various types of elementary particles as well as vacuum fluctuations, black holes, and others. Most of these candidates are unstable to decay and produce photons. So dark matter does not only affect the dynamics of the Universe, but the intensity of intergalactic radiation as well. Conversely, we can use observations of background radiation to constrain the nature and density of dark matter.
By comparing observational data with cosmological theory based on general relativity and particle physics, Dark Sky, Dark Matter reviews our present understanding of the universe and the astrophysics of the night sky and dark matter.

This book deals with the relationship between gravitation and elementary particle physics, and the implications of these subjects for astrophysics. There has, in recent years, been renewed interest in theories that connect up gravitation and particle physics, and in the astrophysical consequences of such theories. Some of these accounts involve a time-variation of the Newtonian gravitational parameter, G. In this respect, the present book may be regarded as a companion to my Cosmology and Geophysics (Hilger, Bristol, 1978). There is some overlap as regards the discussion of G-variability, but the emphasis in the present book is on astrophysics while the emphasis in the other one is on geophysics. The subject is a very broad one indeed, and in giving a review of it I have adopted a somewhat unorthodox way of presenting the material involved. The main reason for this is that a review of such a wide subject should aim at two levels: the level of the person who is interested in it, and the level of the person who is professionally engaged in research into it. To achieve such a two-level coverage, I have split the text up into two parts. The first part (Chapters 1-7) represents a relatively non-technical overview of the subject, while the second part (Chapters 8-11) represents a technical examination of the most important aspects of non-Einsteinian gravitational theory and its relation to astrophysics.