Steady-state model

The steady-state model is a cosmological theory about the nature of our universe. It was once a major alternative to the Big Bang theory. This model is based on the perfect cosmological principle. This principle states that the observable universe is always the same at any time and any place. While a static universe also follows this principle, it cannot explain why space is actually expanding. The steady-state model accepts that the universe expands, but it claims the universe's appearance never changes.

To maintain a constant appearance, the model relies on the continuous creation of matter. In an expanding universe, matter would normally become more spread out over time. This process is known as dilution. To prevent this, the steady-state model proposes that new matter is constantly appearing. This new matter fills the increasing gaps created by expansion. By doing this, the density of the universe remains unchanged. This process ensures the universe looks the same regardless of how much it grows.

There are different ways scientists have thought about these processes. In the 1950s, Thomas Gold and Fred Hoyle considered how new matter might behave. They suggested that newly created matter might exist in regions denser than the average density of the universe. This could create a pressure gradient, which is a difference in pressure between two areas. This gradient might push matter into over-dense regions. This could lead to thermal instability and the emission of large amounts of plasma. However, other scientists found that this would produce more X-rays than we actually observe in space.

History shows a long debate between different cosmological ideas. Albert Einstein studied a steady-state model in a 1931 manuscript, though he eventually abandoned it. In 1948, Hermann Bondi, Thomas Gold, and Fred Hoyle published influential papers on the steady-state model. This period from the 1940s to the 1960s saw the astrophysical community deeply divided. They were choosing between the steady-state model and the Big Bang theory. The Big Bang theory, advanced by Father Georges Lemaître, suggested a universe with a finite age that evolves through cooling and expansion.

Evidence against the steady-state model began to emerge through various astronomical observations. In the 1950s and 1960s, scientists noticed that bright radio sources were unusual. These sources, known as quasars and radio galaxies, were only found at very large distances. Because of the speed of light, seeing them far away means they existed in the distant past. The Big Bang theory predicted this distribution. However, the steady-state model predicted these objects would be found everywhere, including near our own galaxy. By 1961, statistical tests provided strong evidence against the steady-state view.

A major blow to the theory came in 1964 with the discovery of cosmic microwave background radiation. This radiation is a faint glow of light that fills the universe. The Big Bang theory predicted this radiation as a leftover from the early, hot universe. The steady-state model tried to explain it as light from ancient stars scattered by galactic dust. However, the radiation is too even in all directions to be caused by dust. It also lacks the polarization that scattering would create. Furthermore, its spectrum is too close to an ideal black body to be made by many different dust clumps.

In 1993, a new version called quasi-steady-state cosmology (QSS) was proposed. This was suggested by Fred Hoyle, Geoffrey Burbidge, and Jayant V. Narlikar. This model attempted to explain features that the original theory could not. It suggested that creation happens in small pockets over time. These events are sometimes called minibangs or little bangs. Some ideas even linked this to the Planck particle, a hypothetical black hole. Despite these new ideas, most mainstream cosmologists still find flaws in the model. Today, the Big Bang is the widely accepted explanation for the origin of the universe.