Abstract
THE most distant nebuli appear to be receding from us, and the velocity of recession is proportional to the distance. The most commonly accepted explanation of this phenomenon is that due to Friedman and Lemaetre. The principle of their explanation is that it is possible to describe the observed facts by assigning fixed co-ordinates to a distant nebula in a curved space-time in which the metric involves the time t. The spatial interval-distance between the nebula and the observer is then a function of t. The difficulties of this explanation are (1) that it involves the existence of ‘cosmic time’ and restores the distinction between time and space abolished by Minkowski; (2) that it has been impossible to explain why ‘space’ is expanding and not contracting. This theory is a development of the remarkable pioneer theories of Einstein and de Sitter, which contemplated static metrics for space-time. De Sitter's world, it is true, placed time on the same footing as space, but Einstein's cylindrical world introduced cosmic time. More recently (Proc. Nat. Acad. Sci., 18, 213; 1932), Einstein and de Sitter have concluded that at the present moment it is impossible to determine the algebraic sign of the curvature of ‘space’ and that the facts of observation can be described by assigning fixed co-ordinates to a distant nebula in a quasi-Euclidean space expanding with the time.
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MILNE, E. World Structure and the Expansion of the Universe. Nature 130, 9–10 (1932). https://doi.org/10.1038/130009a0
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DOI: https://doi.org/10.1038/130009a0
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