A cosmological model of a universe which is expanding but has the same density at all times due to the continuous creation of matter. The steady-state theory is based on the perfect cosmological principle, which requires the universe to be the same at all times, as well as in all places. The mathematical solution of the equations of general relativity that results from this principle is the de Sitter universe. For many years the steady-state theory was a rival to the Big Bang theory, but it has fallen out of favour because it is inconsistent with the observed properties of the cosmic microwave background and cannot explain the evolution in the appearance of our Universe with time. Unlike the Big Bang theory, the steady-state theory has no initial singularity and does not require the existence of a primordial fireball phase. It was put forward in 1948 by H. Bondi, T. Gold, and F. Hoyle.
Subjects: Astronomy and Astrophysics.