The forgotten cosmological theory

The Well Balanced Universe

 

The forgotten cosmological theory

By Edmund Wood

These days, it is difficult to imagine that the universe might not have started with a big explosion out of a speck of nothingness. So much has been written about the big bang theory and all its associated paraphernalia that most people now think of that description of our cosmos as true fact.

Even just forty years ago, though, the situation was very different. Up till the late 1960s, it was still perfectly acceptable to believe, for instance, that the universe had no beginning at all, and there was a creditable, long-standing theory to support such a view.

The steady state theory of the universe was born in 1948, the brainchild of three Cambridge physicists, Fred Hoyle, Hermann Bondi, and Thomas Gold. These three scientists had been seconded into the same radar development group during the second world war and had become close friends.

After the war, they had each obtained posts back at Cambridge and continued to meet regularly on a social basis. On these occasions, long discussions about controversial topics in physics and astronomy were the norm. Since both Hoyle and Bondi were doing research in astrophysics, it was natural that the current state of cosmology was a recurring theme. Although Gold was working in medical physics, he was also interested in astronomy and contributed many of his own ideas.

Early days

At this time, the modern science of cosmology was very much in its infancy. It was only 19 years since Edwin Hubble had discovered that the light from galaxies was shifted in frequency towards the red end of the spectrum by an amount that depended on distance.

Although most astronomers agreed that this meant that the galaxies were rushing away from each other in an expanding universe, there was as yet no generally accepted opinion as to what this implied about the past and future of the cosmos.

The Belgian theoretical physicist, George Lemaître, had demonstrated that Einstein's equations of general relativity seemed to confirm that the universe was expanding and that it was ever denser going back into the past. More recently — in the mid-1940s — the US physicist, George Gamow, had begun to promote the idea that the universe originally exploded out of nothing and that all the elements were created from a super-dense hot gas of neutrons in the immediate aftermath.

Dissatisfied

The three Cambridge associates were not happy with this proposal of Gamow's; indeed, Hoyle was already researching the possibility that most, if not all, the elements heavier than hydrogen were produced in the centres of stars.

They also thought that it was unscientific to state that the universe suddenly exploded into existence with no determinable cause or reason. A third complaint related to calculations of the age of the universe. If you accepted the explosion-out-of-nothing hypothesis, the age of the universe could be deduced from an estimate of the rate of expansion.

The best estimate at that time gave an age of the universe of approximately two billion years. Unfortunately, this result was lower than the known age of the Earth, calculated from the decay of radioactive elements in ancient rocks. To have the universe younger than the Earth was clearly impossible. While Gamow and colleagues were content to believe that the estimates could be wrong, the Cambridge trio saw the figures as condemnation of the explosion-out-of-nothing hypothesis.

A fundamental principle

A further objection was more philosophical. When Albert Einstein had attempted to apply his equations of general relativity to the whole universe he had introduced the assumption that the universe should look basically the same to any observer at any time. This assumption was known as 'the cosmological principle', and it was thought by some to be of fundamental importance.

At the time, Einstein had been thinking of a static, unchanging universe, because that was before Hubble's work on the galaxy redshifts. To his annoyance, he had found that his universe would be unstable and would collapse into a heap, because of the combined gravity.

He had been reluctant, though, to abandon the cosmological principle, because without it it would have been very difficult to know how to apply the equations to the whole cosmos. Instead, he decided to add an extra factor into the equations, which he called 'the cosmological constant'.

This was the equivalent of a weak, but universal, repulsive force, sufficient to counteract gravity on the large scale, and thus stabilise the cosmos. He was not totally happy with this idea, though, because there was no evidence for such an effect.

Lemaître's expanding universe provided a different resolution of the problem, but at the expense of corrupting the cosmological principle: such a universe changes over time and could only look the same to observers at the same epoch.

In the light of Hubble's results, Einstein decided to accepted Lemaître's solution, and he called the cosmological constant his “greatest blunder”. The Cambridge scientists, however, did not like the distortion of the original principle. They preferred to think of the universe as constant in both space and time, and they now renamed this concept 'the perfect cosmological principle'.

The problem they faced was how to explain all the observations. This was especially difficult since they all three agreed with the majority of astronomers that the redshifts of the galaxies proved that the universe was expanding. Surely, if the galaxies were flying apart, the appearance of the universe would change over time?

A novel idea

It was Gold who came up with a solution. He suggested that new matter could be created 'in the gaps' as everything moved apart, subsequently condensing into new galaxies; this could happen at just the right rate to enable the overall density of matter to remain constant.

At first, Hoyle and Bondi were sceptical about the idea of new matter popping up all over the place, until their calculations showed that in fact the rate necessary was so low it would be undetectable. As Hoyle later phrased it, it would be “about one atom per century in a volume equal to the Empire State Building”.

The new theory was finally presented in two separate papers in the monthly notices of the Royal Astronomical Society in July and August 1948. This was because Bondi and Gold preferred an approach based on philosophical arguments to do with the perfect cosmological principle; whilst Hoyle went for a highly mathematical version, using an adjustment to the equations of general relativity to allow for matter creation.

Hoyle's paper was titled: A new model for the expanding universe, Bondi and Gold's: The steady state theory of the expanding universe”. In a way, this name for the theory was an unfortunate choice, because many people since have confused the steady state universe with a static one. (Perhaps something like 'constant creation theory' would have been better.)

Take off

Initially the new theory received a rather cool reception, because theorists were unhappy with the idea of matter creation with no known mechanism (though Gamow's proposal could also be criticised for this). There were two events, however, which really launched the steady state theory into eminence, particularly in Britain.

In 1949, Hoyle was invited by BBC Radio to give a series of talks on astronomy. These were very popular, and in them he unashamedly promoted the steady state alternative to Gamow's “big bang”, as he called it. (Hoyle's pat description of the explosion hypothesis has stuck ever since.)

Then, in 1957, Hoyle presented a paper together with Margaret and Geoffrey Burbage and William Fowler, which conclusively demonstrated that nearly all the elements heavier than hydrogen were produced in the centres of stars. This was a big blow for the explosion hypothesis, which immediately lost favour, and the steady state theory experienced a surge of support as a result. This subsequent period was the heyday of the theory, and it lasted for several years.

Back to Earth

Despite the undermining of Gamow's proposal for element formation, Gamow himself remained incorrigible regarding the explosion-out-of-nothing hypothesis. In his popular science writing of the period he continued to refer to his “creation of the universe” idea as if it was a true fact.

As it turned out, several occurrences during the 1960s gradually helped to reverse the tide of favour back in his direction.

Firstly, estimates of the age of the big bang universe increased considerably following new measurements of the redshifts and distances of galaxies: the new figures gave a possible age comfortably above that of the Earth.

Secondly, the talented Cambridge radio astronomer, Martin Ryle, produced statistics of the number of radio-emitting sources in the sky compared with their intensities, and these were more in favour of an evolving universe than one with constant density. There had been a history of antagonism between Ryle and the three steady-staters and, even though there was large uncertainty in the data, Ryle ensured that his conclusions were widely publicised with the aid of press conferences.

Thirdly, it was realised that, though most elements had been produced in stars and not in a big, one-off explosion, this did not really negate Gamow's overall concept. In fact, the origins and abundances of the three lightest elements — hydrogen, helium and lithium — were not accounted for in the stellar theory but could be satisfactorily explained by the big bang.

The fourth and most decisive occurrence that changed the fortunes of the two theories was the discovery by Arno Penzias and Robert Wilson in 1965 of a background glow of microwaves coming from every direction in the sky with equal intensity.

It just happened that something similar to this had been predicted by Gamow and his co-workers, Ralph Alpher and Robert Herman, as a possible left-over radiation from their ancient explosion. There did not seem to be any satisfactory way of accounting for this cosmic microwave glow in an expanding, steady-state universe.

It took some time, however, for the discovery of Penzias and Wilson to be fully confirmed, because a large part of the relevant microwave spectrum was only detectable from above the Earth's atmosphere. The steady state theory was consequently able to hold out for several years, but support steadily dwindled.

Into the wilderness

In subsequent years, Hoyle doggedly battled on by producing variations of his theory which were adapted in different ways to accommodate the new observational evidence.

These culminated, in 1993, in the publication, together with Geoffrey Burbage and Jayant Narlikar, of the so-called 'quasi-steady-state cosmology'. This theory describes a universe which is expanding and contracting repeatedly over long periods of time. New matter is created sporadically throughout the universe in mini, big-bang-like explosions in the centres of galaxies. The microwave background is explained as radiation from stars soaked up and re-emitted by cosmic iron whiskers which have been distributed throughout space by supernova explosions.

Since the vast majority of astronomers believe that the big bang theory is right, this and all of Hoyle's previous efforts have generally been ignored by the wider astronomical community, and the original steady state theory itself is now very rarely even mentioned in texts on cosmology.

Bondi and Gold never went along with any of Hoyle's revisions. They believed that these were wrong for the very same reason that they continued to believe that the big bang theory was wrong — because of the failure to comply strictly with the perfect cosmological principle. They remained steadfastly convinced that the universe must look basically the same from any point in both space and time, but they were unable to come up with a new, satisfactory way of explaining how this could fit with all the observations.

© Edmund F Wood Sept 2007

 

More news ...