## On the relation between the expansion and the mean density of the universe

FIRST EDITION IN ORIGINAL WRAPPERS of the introduction of the Einstein-de Sitter cosmological model, the foundation for relativistic cosmology for most of the twentieth century.

Strongly influenced by Edwin Hubble’s evidence for the expansion of the universe, Einstein, in this joint paper with Willem de Sitter finally banishes the cosmological constant, which he had introduced in 1917 to secure a static universe, but which he subsequently regarded as his “biggest blunder."

"In 1932 Einstein and de Sitter proposed that the cosmological constant should be set equal to zero, and they derived a homogeneous and isotropic model that provides the separating case between the closed and open Friedmann models; i.e., Einstein and de Sitter assumed that the spatial curvature of the universe is neither positive nor negative but rather zero. The spatial geometry of the Einstein-de Sitter universe is Euclidean (infinite total volume), but space-time is not globally flat (i.e., not exactly the space-time of special relativity). Time again commences with a big bang and the galaxies recede forever, but the recession rate (Hubble's 'constant') asymptotically coasts to zero as time advances to infinity. Because the geometry of space and the gross evolutionary properties are uniquely defined in the Einstein–de Sitter model, many people with a philosophical bent long considered it the most fitting candidate to describe the actual universe." (*Britannica*). Weil 184.

In: Proceedings on the National Academy of Sciences, Vol. 18 (1932), pp. 213-4. Washington, D.C.: National Academy of Sciences, 1932. Octavo, original printed wrappers. Numerical stamp at top margin of front wrapper. A FINE COPY.

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