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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 steady state views, new matter is continuously created as the universe expands, so that the perfect cosmological principle is adhered to.
The steady state theory of Bondi and Gold was inspired by the circular plot of the film Dead of Night, which they had watched together. Theoretical calculations showed that a static universe was impossible under general relativity, and observations by Edwin Hubble had shown that the universe was expanding. The steady state theory asserts that although the universe is expanding, it nevertheless does not change its appearance over time (the perfect cosmological principle); it has no beginning and no end.
The 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, however, would cause observable effects on cosmological scales. However, 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).
The steady state model is now largely discredited, as the observational evidence points to a Big Bang-type cosmology and a finite age of the universe.
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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 (therefore existing only in the distant past), not in closer galaxies. Whereas the Big Bang theory predicted as much, the Steady State theory predicted that such objects would be found everywhere, including close to our own galaxy.
For most cosmologists, the refutation of the steady-state theory came with the discovery of the cosmic microwave 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.
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. After the observation of an accelerating universe, further modifications of the model were made.[2]
Chaotic Inflation theory has many similarities with steady state theory, however on a much larger scale than originally envisaged. It is the C-field and the notion of quasi-steady state universe that 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 (new hydrogen atoms in the steady state case) can be observed within the observable universe, whereas inflationary theories do not posit inflation as an ongoing process within the observable universe.
Astrophysicist and cosmologist Ned Wright has pointed out flaws in the theory.[3] These first comments were soon rebutted by the proponents.[4] Wright and other mainstream cosmologists reviewing QSS have pointed out new flaws and discrepancies with observations left unexplained by proponents.[5]