Friedmann–Einstein universe

The Friedmann-Einstein universe is a model of the universe published by Albert Einstein in 1931.. The model is of historic significance because it constituted the first scientific publication in which Einstein embraced the possibility of a cosmos of time-varying radius. Interpreting Edwin Hubble's discovery of a linear relation between the redshifts of the galaxies and their radial distance as evidence for an expanding universe, Einstein abandoned his earlier static model of the universe and embraced the dynamic cosmology of Alexander Friedmann. Removing the cosmological constant term from the Friedmann equations on the grounds that it was both unsatisfactory and unnecessary, Einstein arrived at a model of the universe that expands and then contracts.

In the model, Einstein derived simple expressions relating the density of matter, the radius of the universe and the timespan of the expansion to the Hubble constant. With the use of the contemporaneous value of 500 km/s/Mpc for the Hubble constant, he calculated values of 10^-26 cm^-3, 10^8 light-years and 10^10 years for the density of matter, the radius of the universe and the timespan of the expansion respectively. It has recently been discovered that these calculations contain a systematic error..

Einstein chose the Friedmann-Einstein universe as the topic of his 2nd Rhodes lecture at Oxford University in 1931. A record of the lecture, Einstein's Blackboard, can be viewed at the Museum of the History of Science, Oxford.