Getting back to my series on the Big Bang and inflationary cosmology, I'd like to devote the third entry to what for many years was the leading scientific alternative to big bang theory, the Steady State model. Championed by Fred Hoyle, and colleagues Thomas Gold and Hermann Bondi, the Steady State model proposed "a universe that was expanding but which was still truly eternal and essentially unchanging," in the words of Simon Singh's book Big Bang (p. 341).
As noted in the above quote, the Steady State researchers accepted cosmological findings of an expanding universe. To keep the density of galaxies throughout the universe stable over time, even though the universe's expansion would drive existing galaxies further and further apart from each other and thus dilute the concentration of galaxies, required some unorthodox theorizing. According to Singh (p. 345), Gold suggested a process that:
...counteracted the thinning effect of the expansion and resulted in no overall change. This was the idea that the universe compensated for its expansion by creating new matter in the growing gaps between the receding galaxies, so that the overall density of the universe would remain the same.
The proposed constant density in an expanding universe is illustrated graphically here. Singh's Figure 86 on page 346 is also helpful.
The movie Dead of Night, in which events happen but everything at the end of the film turns out to be the same as at the beginning, is said to be an inspiration for Hoyle and colleagues' Steady State model.
Spontaneous creation of new matter, of course, appears to violate the foundational concepts of conservation of mass and of energy.
Georges Lemaitre, the early big bang theorist who was profiled in John Farrell's book, The Day Without Yesterday (which I reviewed here), among others, appears to have found the deviation from the conservation laws objectionable. Writes Farrell (p. 155):
Lemaitre did not agree with the steady state, either. For one thing, although he understood the reason for the theory's violation of the conservation of energy in order to pop hydrogen atoms out of nothingness to stabilize the eternal universe, and that it might be explained by quantum mechanics, he did not see why this one modification of the conservation laws should be singled out -- and not others as well. If conservation of energy should be altered for the sake of fitting a theory, for example, why stop there? Why not modify the other principles if they are not convenient to the theory?
Ultimately, the discovery of the Cosmic Microwave Background, which I will discuss in my next posting, decisively tipped the scales in favor of the Big Bang, as opposed to the Steady State model. Although Hoyle's view of the universe was discredited, it should be noted that his research on stellar nucleosynthesis remains well-respected; his exclusion from the Nobel Prize on the topic is listed among the great controversies in Nobel Prize awards (and non-awards).