The Steady State Theory is a cosmological model that suggests the universe is eternal and unchanging on a large scale. According to this theory, as the universe expands, new matter is continuously created to maintain a constant average density. This means that even though galaxies are moving away from each other, the overall appearance of the universe remains the same over time. Proposed in the 1940s by scientists like Fred Hoyle, the Steady State Theory contrasts with the Big Bang Theory, which posits that the universe had a specific beginning. While the Steady State Theory was popular for some time, it has largely fallen out of favor due to evidence supporting the Big Bang, such as the discovery of cosmic microwave background radiation.