It seems very probable that electromagnetic phenomena will prove to be of great importance in cosmic physics. Electromagnetic phenomena are described by classical electrodynamics, which, however, for a deeper understanding must be combined with atomic physics … No definite reasons are known why it should not be possible to extrapolate the laboratory results in this field to cosmic physics. Certainly, from time to time, various phenomena have been thought to indicate that ordinary electrodynamic laws do not hold for cosmic problems. For example, the difficulty of accounting for the general magnetic fields of celestial bodies has led different authors, most recently Blackett (1947), to assume that the production of a magnetic field by the rotation of a massive body is governed by a new law of nature. If this is true, Maxwell's equations must be supplemented by a term which is of paramount importance in cosmic physics. Hie arguments in favour of a revision are still very weak. Thus it seems reasonable to maintain the generally accepted view that all common physical laws hold up to lengths of the order of the ‘radius of the universe’ and times of the order of the ‘age of the universe’, limits given by the theory of general relativity.

In many respects the astronomical universe has reached the stage of middle-age, with its violent youth behind it and its final stages of senility still safely in the future … It is with some surprise, therefore, that examination of the universe on a small-scale shows so much activity. […]