Steady State Cosmology
A Cosmological Alternative to the Big Bang Theory
The steady state theory was a mid 20th century alternative to the big bang theory. It suggested that there was no moment of creation. The universe has always existed.
Steady State Theory
Most astronomers think some version of the big bang theory is correct, but during the mid-twentieth century the steady state theory was a strong alternative. The cosmic microwave background radiation discovered in the 1960s rang the steady state theory's death knell.
The steady state theory rests on the fundamental cosmological assumption, called the perfect cosmological principle, that the universe does not evolve or change with time on large scales. Hence the universe has existed for an infinite time in the past and will continue to exist for an infinite time in the future, looking like it does now.
Continuous Creation
The steady state theory does not suggest that the universe is static. It came after Hubble discovered the expanding universe and takes the expansion into account.
How can the universe expand without changing? In the steady state theory, hydrogen atoms appear - from nothing - into empty space. They gradually collect to form new galaxies that fill in spaces left between galaxies as the universe expands. This continuous creation of matter keeps the average density of the universe and the average distance between galaxies constant as the universe expands. Hence, an alternate name is continuous creation theory.
Continuous creation violates the principle of conservation of matter, when hydrogen atoms appear in empty space. How can this be, if laws of science are inviolable? The laws of nature are constant, but our understanding of these laws is imperfect and does change. Scientific laws represent our current best understanding of how nature works based on the totality of all experiments and observations. Our statements of all scientific laws are subject to change as required by experimental data.
If matter were continuously created, we would have never seen hydrogen appear from nothing because only one atom need appear every 5 billion years in a cubic meter of space. That translates to roughly one new galaxy per year in the entire observable universe containing billions of galaxies. That rate is insufficient to notice. The steady state theory requires somehow subtly modifying the law of conservation of matter to allow this continuous creation at a rate too slow for us to have observed.
History of the Steady State Theory
In 1946, Thomas Gold, Hermann Bondi, and Fred Hoyle, authors of the steady state theory, saw the movie, Dead of Night, which had a circular structure so that after four parts the end was identical to the start. They wondered if the universe might be like that.
Two years later, Bondi and Gold proposed the perfect cosmological principle: the universe does not change with time. They then proposed the steady state theory. Bondi and Gold suggested that hydrogen atoms appear in space so that the average density of the expanding universe remains constant.
Concurrently Hoyle suggested a mathematical modification of Einstein's general relativity theory that allowed hydrogen atoms to be created from nothing at the needed rate. No experimental evidence to supports or refutes this modification.
During the 1950s and 1960s, the steady state theory was a viable alternative to the big bang. When it was proposed, our best estimate of the age of the universe, in the big bang theory (2 billion years), was less than the age of the Earth. This impossible situation supported the steady state theory. Since then our best estimate for the universe's age has increased to almost 15 billion years, removing this problem for the big bang.
There are philosophical, aesthetic, and theological reasons for preferring either the steady-state or the big bang theory. The big bang has a moment of creation, while the steady state does not.
The weight of accumulated evidence against the steady-state theory, particularly the cosmic background radiation, convinced astronomers that it is incorrect. It remains an important part of the history of cosmology in the twentieth century.
Further Reading
Bondi, Hermann, The Universe at Large, Doubleday, 1960
Hoyle, Fred, Astronomy, Rathbone Books, 1962
Hoyle, Fred. The Nature of the Universe, Harper & Row, 1960
Hoyle, Fred and Narlikar, Jayant, The Physics-Astronomy Frontier, Freeman. 1980
