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How did the steady-state theory explain an expanding universe?

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The steady-state theory proposed that while the universe is continuously expanding, it maintains a constant average density over time.12

To reconcile the observed expansion with a constant density, proponents of the theory—including Sir Hermann Bondi, Thomas Gold, and Sir Fred Hoyle—postulated the continuous creation of matter. This new matter was theorized to form new stars and galaxies at the same rate that older ones became unobservable due to their increasing distance and velocity of recession.12

By continuously generating matter to offset the thinning caused by cosmic expansion, the theory maintained that the universe has no beginning or end and that its large-scale appearance remains unchanged throughout time. However, this model has been largely superseded by the big-bang model, as evidence such as the cosmic microwave background contradicts the steady-state requirement that the universe's properties remain constant.12