In cosmology, the steady-state model believes that the universe is constantly expanding while keeping a steady average density. It also elaborates that matter is constantly being created to give shape to new stars and galaxies at about the same rate that old astronomical objects become invisible due to their progressive distance and rate of the downturn. A steady-state universe has no origin or endpoint in space. Besides, the perspective on the grand scale, that is, the average density and organization of galaxies are identical from any location from inside. Galaxies of all eras are merged.

Sir Hermann Bondi, Thomas Gold, and Sir Fred Hoyle, all British scientists, first proposed the model in 1948. Hoyle expanded on it to address issues that had surfaced in terms of the alternate big-bang theory. Since the 1950s, several studies, especially those of the cosmic microwave aspect, anticipated by the big-bang model, have produced abundant data contradicting the steady-state image, leading scientists to accept the big-bang hypothesis decisively.