Relativity, gravitation and world-structure
Milne takes a 'special relativistic' view of the cosmos, indeed the start of the book is taken up with his derivation of special relativity. This largely corresponds to the (0,0) case in general relativistic cosmology - no cosmological constant, and matter has no large scale gravitational effect. It is interesting to note that this has no particle horizon, which Milne considers as a point in its favour. From his viewpoint a particle horizon would either mean the boundary of the universe meeting matter from 'outside' the universe, or it would imply continuous creation of matter - Milne's religious beliefs made him favour the idea of the universe being created at one point in time.