[excerpt from "Steady-state Theory," Wikipedia]

The steady state theory of Bondi, Gold and Hoyle was inspired by the circular plot of the film Dead of Night they watched together[1]. 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.

[edit] Problems

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. Halton Arp, also since the 1960s, has been taking a different view of the data, claiming that evidence can also point to quasars existing as close as the local Virgo cluster, however, this theory is not accepted by mainstream scientists today.

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,

    The steady state model does not appear to agree with the observed dL versus z relation or with source counts ... In a sense, the disagreement is a credit to the model; alone among all cosmologies, the steady state model makes such definite predictions that it can be disproved even with the limited observational evidence at our disposal. The steady-state model is so attractive that many of its adherents still retain hope that the evidence against it will disappear as observations improve. However, if the cosmic microwave background radiation ... is really black-body radiation, it will be difficult to doubt that the universe has evolved from a hotter, denser early stage.

As of 2006, the majority of astronomers consider the big bang theory 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. Attempts incorporate the cosmic microwave background or the latest measurements of dark energy have lead to the development of quasi-steady state theories.

[edit] C-field

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, creates the matter, and drives the steady expansion of the cosmos. These properties are all shared by the inflaton field used in cosmic inflation. In this fashion Hoyle's conception of the steady state in 1948 incorporates many features that later emerged in inflationary cosmology, especially in 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.

-- Wikipedia, "Steady-state Theory" (as of 2007.01.24)