The Cosmic Microwave Background

The Expansion Of The Universe And The Prediction Of Cmb

The fact that galaxies are moving away from us was first observed in 1917 when Vesto Melvin Slipher noticed that the light of the galaxies (or known as nebulae at that time) that he observed was red shifted, indicative of recession motion of the galaxies. The idea that the universe might be expanding was first demonstrated by Alexander Alexandrovich Friedmann in 1922 after working with Albert Einstein’s theory of general relativity. However, Friedmann’s work was not well received, and Einstein himself insisted on a static universe. Earlier in 1917, in his obstinacy to have an unchanging universe, Einstein introduced a parameter – the cosmological constant – into his equations to yield a static model of the universe. This parameter only has effect on the largest scales; its effect is negligible on the scales of galaxies and smaller, so it will not conflict with the observations and measurements obtained on those scales. A few years later in 1927, Georges Henri Joseph Édouard Lemaître independently rediscovered the solution of an expanding universe when working on Einstein’s equations.