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Steady state theory
In cosmology, the steady state theory (also known as the Infinite Universe Theory or continuous creation) is a model developed in 1948 by Fred Hoyle, Thomas Gold, Hermann Bondi and others as an alternative to the Big Bang theory (known, usually, as the standard cosmological model). In some steady state views, new matter is continuously created as the universe expands, so that the perfect cosmological principle is adhered to. Although the model had a large number of supporters among cosmologists in the 1950s and 1960s, the number of supporters decreased markedly in the late 1960s with the discovery of the cosmic microwave background radiation, and today only a very small number of supporters remain. The key importance of the steady-state model is that as a competitor to the Big Bang, it was an impetus in generating some of the most important research in astrophysics, much of which ultimately ended up supporting the Big Bang theory.
Additional recommended knowledge
The steady state theory of Bondi, Gold and Hoyle was inspired by the circular plot of the film Dead of Night they watched together. Further theoretical calculations that showed that a static universe was impossible under general relativity and observations by Edwin Hubble that the universe was expanding. The steady state theory asserts that although the universe is expanding, it nevertheless does not change its look over time (the perfect cosmological principle); it has no beginning and no end.
The steady state theory requires that new matter must be continuously created (mostly as hydrogen) to keep the average density of matter equal over time. The amount required is low and not directly detectable: roughly one solar mass of baryons per cubic megaparsec per year or roughly one hydrogen atom per cubic meter per billion years, with roughly five times as much dark matter. Such a creation rate would, however, cause observable effects on cosmological scales.
An aesthetically unattractive feature of the theory is that the postulated spontaneous new matter formation would presumably need to include deuterium, helium, and a small amount of lithium, as well as regular hydrogen, since no mechanism of nucleosynthesis in stars or by other processes accounts for the observed abundance of deuterium and helium-3. (In the Big Bang model, primordial deuterium is made directly after the "bang," before the existence of the first stars).
Chaotic inflation theory has many similarities with steady state theory, although on a much larger scale than originally envisaged.
Problems with the steady-state theory began to emerge in the late 1960s, when observations apparently supported the idea that the universe was in fact changing: quasars and radio galaxies were found only at large distances (i.e., redshift, and thus, because of the finiteness of the speed of light, in the past), not in closer galaxies.
For most cosmologists, the refutation of the steady-state theory came with the discovery of the cosmic background radiation in 1965, which was predicted by the big bang theory. Stephen Hawking said that the fact that microwave radiation had been found, and that it was thought to be left over from the big bang, was "the final nail in the coffin of the steady-state theory." Within the steady state theory this background radiation is the result of light from ancient stars which has been scattered by galactic dust. However, this explanation has been unconvincing to most cosmologists as the cosmic microwave background is very smooth, making it difficult to explain how it arose from point sources, and the microwave background shows no evidence of features such as polarization which are normally associated with scattering. Furthermore, its spectrum is so close to that of an ideal black body that it could hardly be formed by the superposition of contributions from dust clumps at different temperatures as well as at different redshifts. Steven Weinberg wrote in 1972,
Since that time, the big bang theory has been considered to be the best description of the origin of the universe. In most astrophysical publications, the big bang is implicitly accepted and is used as the basis of more complete theories.
Bondi and Gold proposed no mechanism for the creation of matter required by the steady state theory, but Hoyle proposed the existence of what he called the "C-field", where "C" stands for "Creation". The C-field has negative pressure, which enables it to drive the steady expansion of the cosmos, whilst also creating new matter, keeping the large-scale matter density approximately constant; in this respect the C-field is similar to the inflaton field used in cosmic inflation. For this reason Hoyle's conception of the steady state in 1948 incorporates many features that later emerged in both inflationary cosmology and the recently observed accelerating universe, which may be modeled in terms of a cosmological constant in Einstein's model of the universe.
The C-field and the notion of quasi-steady state universe also has some resemblance to chaotic inflation theory or eternal inflation which sometimes posits an infinite universe with neither beginning nor end, in which inflation operates continuously, on a scale beyond the observable universe, to create the matter of the cosmos. However, both steady state and quasi-steady state assert that the creation events of the universe can be observed within the observable universe.
Quasi-steady state cosmology (QSS) was proposed in 1993 by Fred Hoyle, Geoffrey Burbidge, and Jayant V. Narlikar as a new incarnation of steady state ideas meant to explain additional features unaccounted for in the initial proposal. The theory suggests pockets of creation occurring over time within the universe, sometimes referred to as minibangs, mini-creation events, or little bangs, somewhat reminiscent of the ambiplasma domains proposed in Hannes Alfven's cosmology. After the observation of an accelerating universe, further modifications of the model were done. Mainstream cosmologists who have reviewed QSS have pointed out flaws and discrepancies with observations left unexplained by proponents. 
External articles and references
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Steady_state_theory". A list of authors is available in Wikipedia.|