Steady State Theory

Expanding universe
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Steady State Theory was a theory proposed in twentieth-century cosmology to explain evidence that the universe was expanding, but still retain the core idea that the universe always looks the same, and is therefore unchanging in practice (and has no beginning and no end). This idea has largely been discredited due to astronomical evidence that suggests the universe is, in fact, changing over time.

Steady State Theory Background and Development

When Einstein created his theory of general relativity, early analysis showed that it created a universe that was unstable — expanding or contracting — rather than the static universe that had always been assumed. Einstein also held this assumption about a static universe, so he introduced a term into his general relativity field equations called the cosmological constant, which served the purpose of holding the universe in a static state. However, when Edwin Hubble discovered evidence that distant galaxies were, in fact, expanding away from the Earth in all directions, scientists (including Einstein) realized that the universe didn't seem to be static and the term was removed.​

Steady state theory was first proposed by Sir James Jeans in the 1920s, but it really got a boost in 1948, when it was reformulated by Fred Hoyle, Thomas Gold, and Hermann Bondi.

(There is an apocryphal story that they came up with the theory after watching the film Dead of Night, which ends exactly as it began.) Hoyle particularly became a major proponent of the theory, especially in opposition to the big bang theory. In fact, in a British radio broadcast, Hoyle coined the term "big bang" somewhat derisively to explain the opposing theory.

In his book, physicist Michio Kaku provides one reasonable justification for Hoyle's dedication to the steady state model and opposition to the big bang model:

One defect in the [big bang] theory was that Hubble, because of errors in measuring light from distant galaxies, had miscalculated the age of the universe to be 1.8 billion years. Geologists claimed that Earth and the solar system were probably many billions of years old. How could the universe be younger than its planets?

In their book Endless Universe: Beyond the Big Bang, cosmologists Paul J. Steinhardt and Neil Turok are a bit less sympathetic to Hoyle's stance and motivations:

Hoyle, in particular, found the big bang abhorrent because he was vehemently antireligious and he thought the cosmological picture was distrubingly close to the biblical account. To avoid the bang, he and his collaborators were willing to contemplate the idea that matter and radiation were continually created throughout the universe in just such a way as to keep the density and temperature constant as the universe expands. This steady-state picture was the last stand for advocates of the unchanging universe concept, setting off a three-decade battle with proponents of the big bang model.

As these quotes indicate, the major goal of the steady state theory was to explain the expansion of the universe without having to say that the universe as a whole looks different at different points in time. If the universe at any given point in time looks basically the same, there is no need to assume a beginning or an end. This is generally known as the perfect cosmological principle. The major way that Hoyle (and others) were able to retain this principle was by proposing a situation where as the universe expanded, new particles were created. Again, as presented by Kaku:

In this model, portions of the universe were in fact expanding, but new matter was constantly being created out of nothing, so that the density of the universe remained the same.[...] To Hoyle, it seemed illogical that a fiery cataclysm could appear out of nowhere to send galaxies hurtling in all directions; he preferred the smooth creation of mass out of nothing. In other words, the universe was timeless. It had no end, nor a beginning. It just was.

Disproving the Steady State Theory

The evidence against the steady state theory grew as new astronomical evidence was detected. For example, certain features of distant galaxies — such as quasars and radio galaxies — weren't seen in nearer galaxies. This makes sense in the big bang theory, where the distant galaxies actually represent "younger" galaxies and nearer galaxies are older, but the steady state theory has no real way to account for this difference. In fact, it's precisely the sort of difference that the theory was designed to avoid!

The final "nail in the coffin" of steady state cosmology, however, came from the discovery of the cosmological microwave background radiation, which had been predicted as part of the big bang theory but had absolutely no reason to exist within the steady state theory.

In 1972, Weinberg said of the evidence opposing steady state cosmology:

In a sense, the disagreement is a credit to the model; alone among all cosmologies, the steady state model makes such definite predictions that it can be disproved even with the limited observational evidence at our disposal.

Quasi-Steady State Theory

There continue to be some scientists who explore the steady state theory in the form of quasi-steady state theory. It is not widely accepted among scientists and many criticisms of it have been put forth that have not been adequately addressed.

Also Known As: steady state cosmology