Big Bang is a past horizon, though in practice our view is also limited by the opacity of the universe at early times. So our view cannot extend further backward in time, though the horizon recedes in space. If the expansion of the universe continues to accelerate, there is a future horizon as well. English astronomer Fred Hoyle is credited with coining the term "Big Bang" during a 1949 BBC radio broadcast, saying: "These theories were based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past." It
Steady state model 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 model 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