Steady-State Theory

There are a number of problems with the steady-state theory, but at the time the theory was proposed, there were also points in its favor.

The steady-state theory rests on the foundation of the perfect cosmological principle. Hence, any evidence that the universe evolves is evidence against the steady-state theory. The existence of quasars and the change in the expansion rate of the universe a few billion years in the past, discussed earlier, are evidence against the steady-state. This evidence for the evolution of the universe did not exist in 1948, when the steady-state theory originated. It became part of the cumulative weight of evidence that had built up against the steady-state theory by the mid 1960s. In gallant attempts to save the steady-state theory, its proponents, chiefly Hoyle and Jayant Narlikar, have argued that the universe can change over time periods of a few billion years without violating the perfect cosmological principle. We must look at even longer time spans to see that these changes with time average out.

The cosmic background radiation is widely considered the final blow to the steady-state theory. Again, proponents of the steady-state theory have made gallant efforts to save their theory in the face of what most astronomers consider overwhelming evidence. They argue that the background radiation could be the cumulative radiation of a large number of radio sources that are too faint to detect individually. This scheme requires the existence of roughly 100 trillion (about 10,000 times the number of observable galaxies) such sources that about are one millionth as bright as the radio sources we do detect. Few astronomers are willing to go to such great lengths to rescue the steady-state theory.

Another objection raised against the steady-state theory is that it violates one of the fundamental laws of physics as that law is currently understood. The law of conservation of matter and energy states that matter and energy are interchangeable and can change between forms, but the total amount of matter and energy in the universe must remain constant. It can be neither created nor destroyed. The steady-state theory requires continuous creation of matter in violation of this law. However, laws of science result from our experimental evidence and are subject to change, not at our whim, but as experimental results dictate. The rate at which matter is created in the steady-state theory is small enough that we would not have noticed. Hence we would not have discovered experimentally any conditions under which matter could be created or any modifications required in this law.

Were there ever any points in favor of the steady-state theory? When the steady-state model was first suggested, our best estimate of the age of the universe in the context of the big bang model was about two billion years. However, the earth and solar system are about five billion years old. The oldest stars in our galaxy are at least 10-12 billion years old. These age estimates present the obvious problem of a universe younger than the objects it contains. This problem is no longer so severe. Modern estimates for the age of the universe range from about 10 billion years to about 20 billion years. The lower end of this range still has the problem, but the upper end of the range gives a universe old enough to contain the oldest objects we have found so far. In the steady-state theory the universe has always existed, so there are no problems presented by the ages of objects in the universe.

For some people there are philosophical or esthetic grounds for preferring the steady-state hypothesis over the big bang theory. The big bang theory has a moment of creation, which some people prefer for personal or theological reasons. Those who do not share this preference often favor the steady-state hypothesis. They prefer the grand sweep of a universe that has always existed to a universe that had a moment of creation and may, by inference, also have an end in some far distant future time.

The weight of evidence against the steady-state theory has convinced most modern astronomers that it is incorrect. The steady-state theory does, however, still stand as a major intellectual achievement and as an important part of the history of the development of cosmology in the twentieth century.