The Einstein-de Sitter Model of the Expanding Universe

The pre-history of the Einstein-de Sitter model will be briefly described here. This cosmological model itself is the subject of the pdf download attached to this page.

Einstein and de Sitter both developed cosmological models in 1917. Einstein obtained a static universe by “tinkering” with his own equations of general relativity… he added the so-called cosmological constant to prevent his presumed static universe from contracting and collapsing under its own gravity.

De Sitter’s model was purely academic in nature, because it contained no matter at all. However, in a universe that expands forever, like is the believe today, the density of matter will eventually become negligible and the universe will approach the de Sitter universe.

In 1922, Friedmann and independently in 1927, Lemaitre, discovered solutions to Einstein’s field equations that contained realistic amounts of matter, but with no cosmological constant. In other words, they accepted that the universe is expanding, as determined by Hubble in 1924. There are 3 possible Friedmann-Lemaitre models:

i) If there is enough matter in the expanding universe, the expansion will one day stop and the universe will contract again - positive space-time curvature.

ii) If there is too little mass in the universe, it will expand forever - negative space-time curvature.

iii) If the amount of matter is “just right”, the expansion rate will approach zero, but the universe will never contract - zero space-time curvature.

In 1932 Einstein and de Sitter together proposed that this “just right” cosmological model be accepted. The Einstein-de Sitter model assumes a homogeneous, isotropic universe, with zero curvature, zero cosmological constant and zero pressure.

To learn more about Einstein-de Sitter universe from an engineering point of view, open the attached pdf file (link below).