In the steady-state model, the density of matter in the expanding universe remains unchanged due to a continuous creation of matter, thus adhering to the perfect cosmological principle, a principle that asserts that the observable universe is basically the same at any time as well as at any place.
Why did it fail?
While the steady-state model enjoyed some minority support in the scientific mainstream until the mid-20th century, it is now rejected by the vast majority of cosmologists, astrophysicists, and astronomers as the observational evidence points to a hot Big Bang cosmology with a finite age of the universe, which the steady-state model does not predict.
Who gave the theory?
The steady-state model was proposed by three physicists in 1948, Hermann Bondi, Thomas Gold, and Fred Hoyle. It is based on the assumption that on the large scale the Universe is completely homogenous; that it looks the same from anywhere in the Universe at any given time.
Why is it Wrong?
At the time, this theory wasn’t quite as crazy due to our lack of understanding of the Universe. The more that we’ve learned about the Universe over the past half-century, the more likely that the steady-state Universe theory is just plain wrong.
The idea of the Steady-state model was to account for some of the problems that were considered from the Big Bang model. The fact that the Universe was calculated to be younger than the Solar System was a big problem with the Big Bang model in 1948.
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Cosmological Principle
In the case of Bondi and Gold, the proposal for a Steady-state model followed their belief in the ‘perfect cosmological principle’, a principle that stated that the Universe should appear the same to all observers at all times. This principle leads to the postulate of continuous creation of matter in order to sustain an unchanging Universe. While the idea bears some similarities to Einstein’s Steady-state model, it is difficult to compare the models directly because the Bondi-Gold theory was not formulated in the context of General Relativity.
On the other hand, Fred Hoyle constructed a Steady-state model of the cosmos by means of modification to Einstein’s field equations. Replacing Einstein’s Cosmological constant with a new ‘creation-field’ term Cik,0, Hoyle obtained the equation
The creation-field term allowed for an unchanging Universe but was of importance only on the largest scales, in the same manner as the Cosmological constant.
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General Theory of Relativity
Hoyle’s Steady-state model violated the law of conservation of energy. However, the theory was more quantitative than the Bondi-Gold model and he extracted estimates of 1.8×1027cm and 5×10-28g/cm3 for the radius and mean matter density of the Universe respectively. These values were similar to the prediction of evolving models. In the years that followed, Hoyle’s Steady-state model became the dominant Steady-state theory because it could be quantified and refined within the context of the general theory of relativity.
For most cosmologists, the definitive refutation of the steady-state model came with the discovery of the cosmic microwave background radiation in 1964, which was predicted by the Big Bang theory.
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