On the significance of Newtonian cosmology

. The theory of newtonian cosmology is re-examined in the light of criticisms by D. Layzer. His two theorems concerning Einstein's law of gravitation substantiate the significance that was assigned to the theory by Milne and McCrea. However, in order to provide analogues of the relativistic models that are newtonian in the strictest possible sense, the theory has to be formulated in terms of a bounded system. But, since this may be arbitrarily large, the dis- tinction between it and an unbounded system is physically scarcely significant. Any extension to an unbounded system necessitates some extension of the definition of newtonian gravitation. Layzer's criticisms make this clear and bring out the difficulty of formulating a satisfactory extension. Nevertheless the extension that he criticises in particular is self- consistent and is the appropriate one in the context.