The science of The Big Bang Theory is revealed! (Of the sit-com that is, not the theory of the origin of the universe.) Last season, I was discussing possible titles for this blog with the writers of the show, who had lots of terrific ideas. After all, that’s what writers do. One of the lead actors passed by, overheard us, and gave us this title over his shoulder, just as he was walking into a scene.
The title “The Big Bang Theory” may originally have been coined in derision. (Of the theory of the origin of universe that is, not the sit-com.) Starting in the 1940’s, Fred Hoyle and other proponents of a theory they called the “Steady State Theory” of the universe, took the observation that the universe expanding as discovered by Edwin Hubble in the 1920’s, and proposed that the universe was constantly generating new matter to fill the new space. They went further to say the new matter was generated at exactly the rate to keep the universe always looking the same at all times.
The Steady-Staters dubbed this idea “the perfect cosmological principle”. “Perfect” because their universe was the same at all times, compared to the more prosaic “cosmological principle”, whose universe is merely the same in all places (homogeneity) and in all directions (isotropy). Some readers may complain that such a cosmological principle is clearly not true. Of course standing on Mars your immediate neighborhood would look quite different than to someone standing (briefly) in the central core of Jupiter. However, the cosmological principle applies only to the universe only on its largest scales, distances crossing many hundreds of galaxies. The principle is an empirical observation, something subject to change if observations ever dictate it. There are even some tantalizing hints in recent data to that effect.
Their rival theory originated a couple of decades earlier, in the 1920’s. A Belgian priest, Georges Lemaître, took guidance from the (then) recent theory of General Relativity by Einstein and proposed that all the matter and energy in the universe was created in a single event and the universe became less dense as it expanded. Perhaps Lemaître, a priest, was pleased with the creation event implicit in the model. The Steady-Staters disagreed with the idea that so much matter and energy could be created in a single event and Hoyle poked fun at Lemaître’s theory by giving it the moniker “The Big Bang” during a radio interview in 1949.
The Steady-State and Big-Bang models each were plausible and provided a good description of the history and evolution of the universe. But at least one had to be wrong. Fortunately, like all useful theories, each made definite and distinct predictions which could be tested by observation. It took several decades, but by now, the Steady-State idea is in conflict with a wide variety of data. For example, the two theories predict a different number of distant galaxies, and the numbers found by astronomers agree with the Big Bang Theory and disagree with the Steady State Theory. Moreover, the relative abundance of elements such as deuterium, helium and lithium compared to hydrogen can be measured. The data are explained well by the entire universe having been a nuclear reactor when it was between about 3 and 20 minutes old, a state which the Big Bang Theory implies the universe must have gone through, but never existed in the Steady State model. The final death knell of the Steady State theory occurred in the 1960’s when a microwave radiation was observed coming from all directions in the sky. This radiation, now known to be the oldest light in the universe is called the “Cosmic Microwave Background”. It was produced when the early universe was hot and opaque, a period that never existed in the Steady State model and which it could not explain.
A more advanced summary of problems with the Steady State idea is given by my friend Ned Wright in his terrific cosmology tutorial.
The Steady-Staters were not crack-pots, and they were certainly not dumb. Quite the contrary, Fred Hoyle was the first to describe how heavy elements were synthesized from hydrogen and helium in stars. Many of the observations which eventually favored the Big Bang Theory took a long time to become convincing. For example, it took decades to unravel what fraction of lithium observed was primordial and what was generated later in cores of stars. The initially predicted age of the universe by the Big Bang Theory made it younger than the oldest stars, a situation only fixed when the difficult to measure expansion rate was finally pinned down.
Even after most of the scientific community favored the Big Bang Theory, Hoyle tried to keep the Steady State theory alive. While some have ridiculed his stance, there is a healthy place in scientific discorse for a few serious-minded skeptics. Hoyle continued to mold the Steady-State Theory to explain the data although the theory necessarily became more and more baroque. Ever the skeptic, later in life Hoyle challenged that biological evolution could be driven by natural selection. However, one of his basic ideas, panspermia, that the building blocks of life may have come to Earth on comets was for a time a serious contender. At least two views of such contrariness can be taken: Perhaps his skepticism caused a sharpening of the mainstream arguments, overall serving science by making its arguments stronger. Or perhaps we are left to take comfort in the adage: Funeral by funeral science marches on.
Perhaps most importantly, had the Steady State Theory been right, the theme song to the show would have been nowhere near as interesting:
The whole universe was in a Steady State.
And nearly 14 billion years ago, nothing special happened, wait…