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{{Infobox theory
| name = Steady State Theory
| type = Cosmological model
| author = Hermann Bondi, Thomas Gold and Fred Hoyle (1948)
| keywords = perfect cosmological principle, continuous creation, [[Big Bang]], [[Quasi-Steady State Cosmology|quasi-steady state]], [[Eternal Universe|eternal universe]]
| year = 1948
}}

'''Steady state theory''' is the cosmological model in which the universe has no beginning and no end, presenting on the large scale the same appearance at every epoch, with new matter created continuously to keep the mean density constant as the universe expands.

==The standard account==

The theory was put forward in 1948 in two papers in the ''Monthly Notices of the Royal Astronomical Society'': one by [[Hermann Bondi]] and [[Thomas Gold]], the other, on a different formal basis, by '''Fred Hoyle'''. Its governing assumption is the '''perfect cosmological principle''' — the universe is homogeneous and isotropic not only in space, as ordinary cosmology assumes, but also in time. There is therefore no privileged epoch, no "early universe," and no origin event.

The model accepted the observed expansion. To keep the perfect cosmological principle in the face of expansion, matter must appear continuously; the required rate is very small, of the order of one hydrogen atom per cubic metre every billion years, far below any rate that could be detected directly. The universe is thus infinitely old, infinitely extended, and always the same in the mean, with galaxies of every age present everywhere at every time.

The steady state model was the principal rival to the evolving hot-origin cosmology through the 1950s and early 1960s. It was Hoyle who gave the rival theory its name, using the phrase "big bang" dismissively in a 1949 BBC broadcast. The model was falsifiable in a way its rival was not: because it forbids evolution, any evidence that the distant — and therefore earlier — universe differs systematically from the nearby one counts directly against it. Three lines of evidence were taken to supply exactly that. Martin Ryle's radio source counts in the late 1950s and early 1960s indicated more sources at large distances than a non-evolving population allows; quasars were found to be distributed in a way suggesting they belonged to an earlier epoch; and in 1965 Arno Penzias and Robert Wilson detected the cosmic microwave background, which the hot-origin model had a natural account of and the steady state model did not. Most astronomers abandoned the theory after 1965.

Hoyle did not. With [[Geoffrey Ronald Burbidge]] and [[Jayant Vishnu Narlikar]] he developed the '''quasi-steady state cosmology''' (QSSC) from 1993, which retains an eternal universe but replaces smooth creation with matter created in discrete explosive events in and near massive objects, and replaces monotonic expansion with a long-term expansion carrying superposed oscillations.

==On this wiki==

Steady state cosmology occupies an unusual position in the literature collected here. Very few contributors defend the 1948 model in its original form; a great many share its central commitment — that the universe had no beginning — while rejecting the expansion the model was built to accommodate. That distinction matters when reading the papers below, and it is set out at [[Eternal Universe]].

The direct descendant of the theory is represented by [[Geoffrey Ronald Burbidge]], Hoyle's long-time collaborator, whose ''[[Quasi-Steady State Cosmology]]'' (2001) argues that the standard model "does not have the strong observational foundations that are frequently claimed for it" and that only two of its properties — the expansion and the acceleration — were ever genuinely predicted rather than fitted after the fact. [[Jayant Vishnu Narlikar]], the third member of that collaboration, is catalogued here for ''[[A Different Approach to Cosmology: From a Static Universe through the Big Bang towards Reality]]'' (with Hoyle and Burbidge), ''[[Facts and Speculations in Cosmology]]'', ''[[An Introduction to Cosmology]]'' and ''[[Current Issues in Cosmology]]''. The founding pair are both catalogued: [[Hermann Bondi]] and [[Thomas Gold]]. See also ''[[A Tribute to Fred Hoyle]]''.

[[Thomas E Phipps]] argued in ''[[Steady-State Cosmology: Once More Unto the Breach?]]'' (1989) that a non-Doppler redshift mechanism together with [[Paul Marmet]]'s treatment of [[Olbers' Paradox|Olbers' paradox]] justified renewed interest in steady-state and related models, citing [[Halton C Arp]]'s quasar data in support. [[Mogens True Wegener]] derived three new steady-state models from a strict light principle in [["Big Bang" or "Steady State"?]] (2007), and [[Alphonsus G Kelly]] argued in ''[[Big Bang or Full Stop?]]'' (2005) that the redshift data, correctly read, indicate a recession that has slowed to a present steady state.

A larger group here reaches an eternal universe by a different route — denying that the redshift measures recession at all, so that no expansion needs to be balanced by creation. That literature is gathered at [[Redshift]], [[Tired Light]] and [[Intrinsic redshift]], with representative papers including ''[[An Infinite Non-Expanding Universe in Dynamic Equilibrium]]'', ''[[Nature of the Non-Expanding Universe]]'' and ''[[A Non-Expanding, Non-Relativistic Universe]]''. On that view the steady state theory conceded too much by accepting expansion in the first place. Wider criticism of the standard model is indexed at [[Big Bang]] and [[Non-standard cosmology]], and further material is under [[:Category:Cosmology]].

==Open questions==

That the steady state theory in its 1948 form is inconsistent with the microwave background and the radio source counts is not seriously disputed, including by most critics here. What remains genuinely open in mainstream cosmology is narrower: the origin of the matter–antimatter asymmetry, the physical status of inflation, and whether the standard model's own creation event is better founded than continuous creation was. Critics on this wiki press the last point hardest, arguing that a single unexplained creation is not obviously preferable to a distributed one.

==See also==

* [[Big Bang]]
* [[Eternal Universe]]
* [[Non-standard cosmology]]
* [[Redshift]]
* [[Quasar]]
* [[Cosmology]]

[[Category:Cosmology]]
[[Category:Big Bang]]
[[Category:Astronomy]]
[[Category:Theory & Models]]

Steady State Theory - Revision history

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