Steady state universe

In cosmology, the Steady State theory is an alternative to the Big Bang model of the evolution of the universe. In the steady-state theory, 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.

While the steady state model enjoyed some popularity in 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.

Cosmological expansion was originally discovered through observations by Edwin Hubble. Theoretical calculations also showed that the static universe as modeled by Einstein (1917) was unstable and contradicted general relativity. The modern Big Bang theory is one in which the universe has a finite age and has evolved over time through cooling, expansion, and the formation of structures through gravitational collapse.

The steady state theory asserts that although the universe is expanding, it nevertheless does not change its appearance over time (the perfect cosmological principle); the universe has no beginning and no end. This requires that matter be continually created in order to keep the universe's density from decreasing. Influential papers on steady state cosmologies were published by Hermann Bondi, Thomas Gold, and Fred Hoyle in 1948.

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