The twentieth century was in many ways revolutionary in the history of cosmology. In fact, it can be argued that cosmology as a science in its empirical sense was born during this time: the advances in the field of astronomy allowed scientists to gain observational data that came to play a crucial role in the development of the discipline. The twentieth century also was a period of scientific controversy, a struggle between two cosmological concepts, namely the Big Bang and the Steady State theories. In this essay I shall explain why the Steady State theory of cosmos came about by investigating the context in which it was developed. I shall illustrate that the theory was in a sense the result of the developments in cosmology in the first half of the century, while at the same time it can be seen as a reaction to those changes. Secondly, I shall analyze the history of the conflict between the two theories and examine why the Steady State theory is now regarded obsolete. I shall illustrate that the current observational evidence is in disagreement with the predictions of the Steady State theory and, by contrast, strongly correlates with the description of the universe provided by the Big Bang theory. In this essay I shall refer to Thomas Kuhn’s concepts, such as ‘anomaly’, ‘paradigm shift’ and ‘crisis’, as described in his book The Structure of Scientific Revolutions. I believe these terms will be helpful in understanding the story of the Steady State theory.
To start with, what does the Steady State theory argue? The Steady State theory was a cosmological concept put forward by Fred Hoyle, Hermann Bondi and Thomas Gold in the late 1940s, at the same time when George Gamow and Ralph Alpher formulated their Big Bang theory. In contrast with the Big Bang theory, the Steady State theory claimed that the universe was expanding ‘statically’, meaning that its large-scale properties did not change with time. The idea was based, as Hoyle points out, on a ‘symmetry postulate’, which, as he argued, ‘had repeatedly demonstrated their power in theories of physics’ by that time in the twentieth century (Hoyle, 1955, p. 157). The proponents of the theory put forward the idea of the ‘perfect cosmological principle’, according to which the universe must look the same to its observers not only from all the points in space, but also from all the points in time, which was achieved by the continuous process of creation of matter to ‘fill in the gaps’ that were generated by the expansion of the universe. The theory, according to Hoyle, ‘had a compelling simplicity’ due to the underlying principle of ‘symmetry postulate’ (Ibid). Hoyle himself gave a humorous account of how the idea of the Steady State universe was conceived: Hoyle and his colleagues, Bondi and Gold, were inspired after seeing a film that ended the same way it had begun, ‘thereby setting-up the potential for a never-ending cycle’ (Hoyle quoted in Longair, 2006, p. 324). The steady-state model was in a stiff competition with the Big Bang theory, which eventually came to be regarded as the basis of the current scientific consensus among cosmologists. However, I shall argue that both theories emerged as a result of a series of developments in cosmology and astronomy in the first half of the twentieth century.
To be able to understand what triggered the emergence of the Steady State theory in the middle of the twentieth century it is essential to briefly outline the earlier history of the cosmology. In this section of my essay I shall examine the evolution of cosmology as a scientific discipline in the first part of the twentieth century. The birth of modern cosmology is often associated with the emergence of Albert Einstein’s theory of relativity and, in particular, with its application to cosmology in his Cosmological Considerations in the General Theory of Relativity published in 1917. In this paper Einstein’s tackles problem of ‘formulating boundary conditions of infinite space’, which had been considered by Isaak Newton two centuries earlier, and solves the problem by postulating a closed model of the cosmos, spatially finite but temporarily infinite (Kragh, 2002, p. 525). Einstein aimed to reconcile his general theory of relativity with the scientific consensus in cosmology, namely the ‘static’ model of the universe. Among the problems associated with this view was the fact that such a static universe was an unstable system and prone to a collapse due to the forces of gravity. Einstein solved this problem by adding a cosmological constant to counterbalance gravity and ensure the stability of the universe (Kragh, 1996).
As I have stated earlier in this essay, the scientific consensus in cosmology at the time, or the ‘paradigm’, using Thomas Kuhn’s term, was the static universe. Hence, the introduction of the cosmological constant by Einstein can be viewed as an attempt to accommodate the ‘anomaly’ that was derived from his field equations: the fact that, according to general relativity, the universe must either collapse or expand indefinitely (Nussbaumer, 2009). The idea of an expanding universe seemed unintelligible at the time. Nevertheless, the paradigm of a static universe was undermined and was eventually refuted in the early 1930s. As Kragh points out, the refutation of the static universe was the result of two different scientific endeavors, one of which was observational and the other theoretical (Kragh, 2002). The observational evidence in favor of an expanding model of the universe was accumulated later in the 1920s. This came to be known as the Doppler effect: the light that came from faraway objects in space appeared to be ‘redshifted’, which could be explained by the fact that they were receding from the Earth. Redshifts had been observed earlier: Vesto Slipher is considered to be the first to systematically study redshifts in nebulae in 1910s (Nussbaumer, 2009). However, the idea of an expanding universe was not accepted until 1929, when Edwin Hubble published his data, postulating what is now referred to as Hubble’s Law, according to which the recessional velocities of the galaxies that were moving away from the Earth were proportional to their distances from the Earth (Ibid).
The theoretical basis for an expanding universe, however, had been put forward years earlier. In this section I shall briefly outline the contribution of Alexander Friedman, who is generally regarded as the first person to consider the theoretical possibility of an expanding universe. In 1922, years before Hubble published his data, Friedman derived what are now referred to as the Friedman equations, which describe the universe as homogenous and isotropic. However, the Friedman equations were capable of generating different cosmological models. Among such were models that proposed the idea of an indefinite expansion of the universe and, hence, would be compatible with what came to referred to as the Big Bang theory, as well as the model based on the idea of a ‘static’ expansion, which is the cosmological model that was proposed by the Steady State theory in 1948 (Nussbaumer, 2009). George Lemaitre explicitly argued in favor of an expanding universe in the late 1920s, and in 1931 he put forward the concept of the ‘primeval atom’, which is generally regarded as a precursor to the Big Bang theory (Bertotti, 1990).
Hence, the Steady State theory, just like the Big Bang theory, was in a sense the result of a continuous development in both theoretical and observational cosmology. However, it is essential to look at the further development of cosmological ideas and examine why both theories did not become fully formulated until the late 1940s. As Kragh states in his paper, ‘It is most remarkable that neither Friedman’s nor Lemaitre’s works made no impact at all’ (Kragh, 2002, p. 527). He states that among the reasons for the reluctance of the scientific community to accept the new paradigm was the ‘ingrained belief in the static nature of the universe’ (Kragh, 2002, p. 527) The use of Thomas Kuhn’s concept of ‘crisis’ can be helpful in understanding the state of cosmology in the period that began with the discovery of an expanding universe: ‘The 1930s witnessed a proliferation of cosmological ideas and models that were opposed to standard general relativity. On the whole, cosmology had very little disciplinary and theoretical unity’ (Kragh, 2002, p. 529). The fact that the universe was expanding led to a ‘paradigm shift’ in cosmology, namely, the shift from a static to an expanding universe. However, this change was a gradual process: during the period of crisis a number of ideas were put forward by cosmologies in order to solve the ‘anomaly’ of an expanding universe. The period of crisis eventually resulted in a competition between two cosmological theories, the Big Bang and the Steady State theory. Taking the context of crisis into account, it can also be argued that the Steady State theory came about as a compromise between the two paradigms: while the theory accepted the fact that the universe was expanding, it described the expansion as ‘static’, meaning that the large-scale properties of the universe remained stable. Indeed, the early big bang theories in the 1930s were, as Kragh puts it, ‘cooly received’ due to their idea of the creation of the universe, which was considered to be ‘conceptually problematic’ (Kragh, 2002, p. 528). Hence, I shall argue that the primary reason for the emergence of the Steady State theory in the 1940s was to solve the ‘anomaly’ of an expanding universe by putting forward a cosmological model that would not refer to a hypothetical beginning of time and would retain some of the features of the ‘static universe’ paradigm. In this sense, the Steady State theory can be compared with the geoheliocentric model devised by Tycho Brahe in the sixteenth century as an alternative to Copernicus’s model and, hence, also represented a consensus between two competing paradigms: heliocentrism and geocentrism (Westman, 2011).
But what other factors could have contributed to the formulation of the Big Bang and Steady State theories? Why were they formulated in the immediate post-war period? Among the other factors that led to the advancement of the Big Bang theory as well as the formulation of the Steady State theory were the developments in nuclear physics that came to be a fundamental component of modern cosmology. According to Kragh, the advances in nuclear physics provided cosmology with a ‘much-needed physical perspective’ (Kragh, 2002, p. 530). What is more, Jon Agar uses his concept of working worlds to explain the emergence of both cosmological theories in the post-war period by stating that ‘the cosmologies devised in the middle of the twentieth century had at their heart the scientific values of the working world of nuclear projects’ (Agar, 2012, p. 366). In 1940s George Gamow combined Friedman equations with nuclear physics to explain how the universe came into being. Fred Hoyle in turn developed his theory of nucleosynthesis that came to be regarded as a crucial contribution to modern cosmology (Kragh, 1996).
However, the Steady State theory was a rival concept to theory of Big Bang theory from its very beginning. So, what was the reason for the scientific controversy in the middle of the twentieth century? There were a number of problems that the supporters of the Bing Bang theory faced at the time. I have already mentioned earlier in this essay the more general and philosophical objections based on the problem of the creation of the universe out of nothing. Hoyle coined the term ‘big bang’ as a derogatory label, since he did not consider the theory scientific: ‘For it is against the spirit of scientific enquiry to regard observable effects as arising from ‘causes unknown to science’, and this is in principle what creation-in-the-past implies’ (Hoyle quoted in Harrison, 1981, p. 380). The notion of the creation of the universe seemed to violate the concept of laws of nature, whereas the idea of continuous creation as put forward by the Steady State theory was seen as scientific due to its regular nature. However, in addition to this, there were serious scientific objections to the Big Bang theory at the time. In particular, one of the main problems was the ‘time-scale difficulty’ associated with the theory. As a result of overestimation of the value of the Hubble constant, the universe as described by the Big Bang theory appeared to be younger than the Earth (Kragh, 1999). In addition to this, the Big Bang theory did not have empirical evidence that would prove the fact of the emergence of the universe from a hot dense state at the time. However, it is important to note that the concept of a steady-state universe as well possessed certain disadvantages that were pointed out after its introduction to the scientific community. First of all, the Steady State theory was considered to be unorthodox mainly because of its notion of continuous creation of matter, which, it can be argued, was as problematic, as the notion of the creation of the universe put forward by the Big Bang theory. What is more, the Steady State theory violated the principle of energy conservation and, hence, the theory was often referred to, according to Kragh, as ‘unscientific romanticizing’ or ‘science-fiction cosmology’ (Kragh, 2002, p. 531).
So, why did the Steady State theory eventually become refuted as a cosmological model of the universe? In the following section of this essay I shall provide a description of that process by examining the accumulation of evidence in support of the Big Bang theory, which eventually led to refutation of the steady-state concept. To begin with, in 1952 William Baade discovered that the Hubble’s constant had been overestimated, which led to its further reconsideration by astronomers and its revision downwards. As a result, one of the major objections to the Big Bang theory was no longer valid: ‘With a new Hubble time of 3, 6 billion years, soon to increase to about 10 million, there was no longer any serious difficulty with the age of the universe' (Kragh, 2002, p. 532). Empirical objections to the Steady State theory, which also provided evidence for the Big Bang concept, came from radio astronomy in the 1950s. Hoyle wrote in 1956: ‘Recently Martin Ryle in England reported a count of radio sources which indicated that the density of galaxies in space increases with distance from us – again an apparent support for the evolutionary hypothesis’ (Hoyle, 1956, p. 166). The evidence appeared to contradict the Steady State theory, which argued that the density of the universe must be constant (Longair, 2006). In the early 1960s, having gathered further evidence Martin Ryle wrote that ‘these observations do appear to provide conclusive evidence against the steady-state theory’ (Kragh, 2002, p. 533). The data that came from radio astronomy seriously damaged the reputation of the Steady State theory, but the theory had not been conclusively refuted yet. The competing two theories in the period of crisis required what Karl Popper referred to as a ‘crucial experiment’, or, in this case, observation, which would enable the scientists to decide between the two competing hypotheses. It was in the 1960s, when new astronomical data led to the rejection of the steady-state hypothesis and the acceptance of the Big Bang theory as the new cosmological paradigm. Such evidence included the count of quasars and the cosmic helium abundance (Kragh, 1996). However, the moment of triumph for the Big Bang theory came in 1965 with the discovery of the cosmic microwave background radiation by Arnold Pensias and Robert Wilson. The discovery, which had been predicted earlier by the supporters of the theory, detected the relics from the early stages in the evolution of the universe after its expansion from a hot dense state (Longair, 2006). This discovery can be termed as ‘the crucial experiment’ in Karl Popper’s sense, as it enabled cosmologists to choose between the two rival theories: while it had been predicted by the Big Bang theory, it could not be accounted for by the Steady State theory. Hence, due to the overwhelming evidence in favor of the Big Bang theory, the steady-state cosmological model was rejected by the scientific community and since then has been generally considered obsolete (Ibid).
To sum up, in this essay I have investigated the history of the Steady State theory starting with the early developments in cosmology, namely Einstein’s application of relativity to cosmology and the emergence of the paradigm of an expanding universe in the early 1930s. Cosmology entered a phase of crisis, where it had to devise a new theory that would be able to explain the expansion of the universe. The early Big Bang theories did not receive much support due to a number of problems associated with the notion of the creation of the universe, as well as due to overestimation of the value of the Hubble parameter. In the late 1940s, in the context of the advances in nuclear physics, the Steady State theory emerged as an alternative to the Big Bang theory. While it accommodated the fact of the expansion of the universe, it postulated the idea of continual creation of matter, which meant that the universe remained static in its large-scale properties. While being a serious competitor to the Big Band theory in the middle of the century, it was eventually refuted as a result of new data gathered by astronomers, which contradicted the steady-state concept and, by contrast, matched with the predictions of the Big Bang theory. The latter was accepted as the new paradigm in cosmology in the 1960s, crucially after the discovery of cosmic microwave background radiation. The Steady State theory, on the other hand, has since been generally rejected, as it cannot account for the observational data gathered by astronomers.