Steady-state model
This article is about astronomy. Steady state is also a central term in the biochemical field of enzyme kinetics.
The steady state theory is a non-standard cosmological view developed in 1949 by Fred Hoyle and others as an alternative to the Big Bang theory. According to the steady state theory, although the universe is expanding, it nevertheless does not change its look over time, because new matter is formed to keep the density equal. Because only very little matter needs to be formed, roughly a few hundred atoms of hydrogen in the Milky Galaxy each year, it is not a problem of the theory that the forming of matter is not observed directly. However, Halton Arp claims to have observed the outpouring of matter from active galactic nuclei, and uses the steady-state theory as a basis for theoretical understanding of his observations.
Problems with the steady state theory began to emerge in the late 1960s, when evidence started to show that the universe was in fact changing: quasars and radio galaxies were found only at large distances (and thus, because of the finiteness of the speed of light, in the past), not in closer galaxies. The final blow came with the discovery of the cosmic background radiation in 1965 which was predicted by the big bang theory. Proponents of the steady-state theory also predicted values of the CMB throughout the 1900's, however inertia was with the Big Bang at the time the CMB was finally observed.
Today, the big bang theory is the one that the majority of astronomers consider the best approximation to describing the origin of the universe. In nearly all astrophysical publications, the big bang is inherently accepted and is used as the basis of more complete theories.
Observational cosmologists deal with observations, and because the universe and the speed of light are both finite, one can only observe data within a sphere centered on the observers. What is outside that sphere is therefore not accessible to observational cosmologists.
Some Theoretical cosmologists regard the big bang model as incomplete in part because it does not address the issue of what happened before the big bang. Some of these speculations about what happened before the big bang (and what would happen after the Big Crunch) are qualitatively somewhat similar to the quasi-steady-state model.