… the grounds on which homogeneity is generally assumed appearing to be those of convenience rather than generality … We must categorically dissent from the extreme idea … that homogeneity is included in the definition of the universe … We take it to be perfectly conceivable that an increase of telescopic power may reveal a variation of material density with distance, and the denial of this possibility … seems to us to be inconsistent with the fundamental principles of science. We hold that the assumption of spatial homogeneity is … a working hypothesis, valid so long as it does not conflict with observation or with theoretical probability, and justifiable during that time as a restriction on arbitrary speculation … we have no grounds for supposing that the part of the universe which is observed is typical of the whole … the phenomena we embody in our models may be purely local characteristics … while, in the present state of knowledge, a spatially homogeneous universe has greater claims to consideration than any other, such claims … have no a priori justification.