The Andromeda Galaxy (M31), the nearest spiral galaxy to our own Milky Way, about 2,400 million light-years distant, and part of our local group of galaxies.
14 October 2022
The Big Bang is the name given to a variety of models that explain how the universe suddenly began expanding from an incomprehensibly dense and hot state some 13.8 billion years ago.
The modern idea of an expanding universe was first proposed by Belgian physicist (and Catholic priest) Georges Lemaître in 1927. Two years later astronomer Edwin Hubble would provide the observational basis that confirmed Lemaître’s model. Four years later, Lemaître updated his idea of an expanding universe with the proposal that the universe began with the explosion of l'atome primitive (the primeval atom). The theory was developed further in the late 1940s by physicists George Gamow and Ralph Alpher, resulting in a joint paper for which Gamow recruited physicist Hans Bethe as a co-author—even though Bethe had made no substantive contribution to the work—so he could make an alpha-beta-gamma pun. (Alpher, who was a graduate student at the time, objected to the pun as it diluted his contribution to the work—and in academia, credit is everything, especially to early-career researchers.)
In these early years, while there was a solid observational foundation for the expansion of the universe, the Big Bang theory lacked substantial observational confirmation. It wouldn’t be until the 1965 discovery of the cosmic microwave background radiation, the residue of the Big Bang, that the theory became generally accepted. In these early years, the chief theory competing with the Big Bang was the Steady State theory, championed by English astronomer Fred Hoyle. And it was Hoyle who first coined the term big bang to describe the competing theory. He did so in a March 1949 BBC broadcast, a transcript of which was printed the following month in the BBC’s weekly magazine, the Listener:
We now come to the question of applying the observational tests to earlier theories. These theories were based on the hypothesis that all the matter in the universe was created in one big bang at a particular time in the remote past.
[…]
But [Hoyle’s “continuous creation” hypothesis] replaces a hypothesis that lies concealed in the older theories, which assume, as I have already said, that the whole of the matter in the universe was created in one big bang at a particular time in the remote past. On scientific grounds this big bang hypothesis is much less palatable of the two. For it is an irrational process that cannot be described in scientific terms. Continuous creation, on the other hand, can be represented by precise mathematical equations whose consequences can be compared with observation. On philosophical grounds too I cannot see any good reason for preferring the big bang idea.
That same issue of the Listener published a letter by an A.G. Walker responding to Hoyle’s broadcast that also used the term:
Mr. Hoyle suggests that his hypothesis is not additional but replaces a creation hypothesis in previous theories, and that in these theories the universe is assumed to have been created instantaneously, “with a big bang” as he put it. In fact these theories say nothing at all about the mechanism of creation. Scientists as individuals may have ideas on this subject but not science, at least not the theories prior to Mr. Hoyle’s. In cosmology the “epoch of creation” is the epoch when physical laws first existed pretty much as they are today, and no scientific theory can take us back beyond that epoch. What happened before then, whether matter existed in a different form or whether there was a “big bang,” is something about which science, the study of observables, can tell us nothing.
Hoyle would go on to give a five-part lecture series on the BBC in early 1950, and in the final part, broadcast in March 1950, he would use big bang again:
First I will consider the older ideas—that is to say the ideas of the nineteen-twenties and the nineteen-thirties, and then I will go on to offer my own opinion. Broadly speaking, the older ideas fall into two groups. One was that the Universe started its life a finite time ago in a single huge explosion, and that the present expansion is a relic of the violence of this explosion. The big bang idea seemed to me to be unsatisfactory even before detailed examination showed that it leads to serious difficulties.
[…]
From time to time people ask where the created material comes from. Well it does not come from anywhere. Material simply appears—it is created. At one time the various atoms composing the material do not exist and at a later time they do. This may seem a very strange idea and I agree that that it is but in science it does not matter how strange an idea may seem so long as it works—that is to say so long as the idea can be expressed in a precise form and so long as its consequences are found to be in agreement with observation. In any case the whole idea of creation is queer. In the older theories all the material in the Universe is supposed to have appeared at one instant of time, the whole creation process taking the form of one big bang. For myself I find this idea much queerer than continuous creation.
Hoyle’s use of the term was mildly derisive, but proponents of the Big Bang theory adopted it and made it their own. Hoyle was wrong in his assessment of the theory, but to be fair when he initially expressed his doubts, those doubts were justified given the state of the science at the time. But Hoyle never accepted the theory’s validity, even after the evidentiary support for the theory became overwhelming, which is a mark against him. Hoyle died in 2001.
And while the overall concept of the Big Bang is generally accepted by physicists, no single model of how it happened adequately explains all the observations, so the debate on the exact nature of the Big Bang and the subsequent expansion of the universe continues.
Sources:
Hoyle, Fred. “Continuous Creation.” The Listener, 7 April 1949, 568. Gale Primary Sources: The Listener.
———. “Man’s Place in the Expanding Universe.” The Listener, 9 March 1950, 420–21. Gale Primary Sources: The Listener.
Oxford English Dictionary, third edition, December 2008, s.v. big bang, n.
Walker, A.G. “Continuous Creation” (Letter). The Listener, 7 April 1949, 588. Gale Primary Sources: The Listener.
Photo credit: Dave Wilton, 2022.