In the light of these results, the question at issue is not whether our universe is an Einstein universe or a de Sitter universe, but rather how far it has travelled along the road which begins with an Einstein universe and ends with a de Sitter universe. Whatever the answer may be, we are led to suppose that at the beginning of time the nebulae were much nearer to one another than they now are, that ever since then they have obeyed their inherent tendency to scatter, or rather the tendency of the flowing stream of time to scatter them, and that they are now moving away from us, and from one another, with speeds which are proportional to their distances. This is in accordance with Hubble’s conclusion, that the apparent speeds of recession of the nebulae are roughly proportional to their distances. From Hubble’s data Eddington has calculated that the original Einstein universe must have had a radius of about 1200 million light-years. If the apparent speeds of recession of the nebulae had been found to be strictly proportional to their distances, we could have explained everything by supposing that we lived in an expanding universe, which had started as an Einstein universe of 1200 million light-years’ radius, had now expanded to something of the order of 2000 million light-years’ radius, and was destined to go on expanding to all eternity. This provides a simple and rather fascinating picture of the universe, but there are many reasons against supposing that it is a true one. In the first place, if we interpret the spectral displacements as evidence of velocity alone, the speeds of the nebulae are probably very far from being (as the foregoing picture would require) accurately proportional to their distances from us. A group of three nebulae, all believed to be at the same distance of about 50 million light-years, differ by nearly 2000 miles a second in their speeds, which average about 5000 miles a second. Oort has found a general tendency for the speeds of very distant nebulae not to be strictly proportional to their distances. At from 20 to 40 million light-years the apparent divergences average 750 miles a second, but it is not clear how far these result merely from inaccurate estimates of the distances of these remote nebulae.