Only a whimper in face of the big bang?

Against the big bang, steady-state theorists are on a mission to deprogramme a generation of young fogeys, says Roger Blandford

Cosmologists are always in error, though never in doubt." This aphorism, attributed to the Russian physicist Lev Landau, sprang to mind as I read through this book. The senior author is Fred Hoyle, who is best known as an outspoken advocate of the "steady state" model of the universe, which he proposed in 1948 (simultaneously with Hermann Bondi and Thomas Gold, and following earlier suggestions by James Jeans and Paul Dirac), and as a lucid populariser and science-fiction author. Hoyle can also be credited with leading a revolution in British astrophysics, recognising early on that it had to free itself from the protective embrace of applied mathematics and go out into the heady world of discovery in nuclear and particle physics if it was to meet the challenges of large telescopes opening up the whole electromagnetic spectrum. The second author, Geoffrey Burbidge, was one of the first astrophysicists to appreciate the enormous energy associated with extra-galactic radio sources, and one of Hoyle's collaborators in developing the theory of nucleo-synthesis, a crown jewel of 20th-century astrophysics. Third, there is Jayant Narlikar, who is a distinguished relativist, educator and populariser.

These three authors have a mission to deprogramme a generation of young fogeys, whom they see as having been lulled into an uncritical acceptance of false prophets and cosmological orthodoxy, with an unashamed polemic written in a lively and entertaining style. I think (and hope) they would be proud to be labelled Old Turks.

Orthodox cosmology, or the "big bang theory" (a phrase coined by an ironic Hoyle), has been assembled (albeit with some back-tracking) through patient and painstaking observations and by sifting through many imaginative theoretical ideas over the past 40 years. It assumes that our universe emerged at a specific time from a very dense state, where quantum mechanics and gravity held sway. The universe underwent a growth spurt, called "inflation", and created a space that is extremely "flat", just as Euclid postulated, and uniform, save for some tiny blemishes. It then grew more moderately, allowing all the interactions of high-energy physics to take place and leaving behind a slight residue of matter over anti-matter. After 300 million years, the minor blemishes left over from inflation had grown to form the first associations of stars and galaxies and their byproducts, planets. Finally, if the interpretation of recent observations is to be trusted, we appear to be embarking on a second burst of inflation, where the universe will double in size about every 12 billion years. Both episodes of inflation have been attributed to "dark" or "vacuum" energy, a counter-intuitive feature of space in its most fundamental state. As the authors remark, reactions to this modern creation myth range between "fanatical belief and cynical scepticism", although most astrophysicists take the view that it is a good working model that has been and should be tested as precisely as possible. All are agreed that it raises more questions than it answers.

The steady-state cosmology starts from the opposite assumption: that we live in an eternal universe where the dilution caused by expansion is compensated by the continuous creation of matter. There never was a high-density state, and helium formation is associated either with nuclear burning in stars or matter creation itself. The original version of the theory has some similarities with the contemporary theories of first or second inflation, with a so-called C-field taking the place of dark energy. Like the big bang theory, steady-state cosmology has been modified over the years to accommodate new observational discoveries and retains a strong emotional appeal. But after all, when faced with a choice between a celestial empire on which the sun, in an almost literal sense, never sets and one that rushes purposelessly towards darkness and emptiness - an agoraphobic's worst nightmare - who would not opt for life? However, in science, even the most beautiful theories can be murdered by ugly facts.

This is neither a popular nor even a pedagogic book. The field equations of general relativity are introduced early on, without explanation, and quickly developed in ways both standard and non-standard. A good working knowledge of the jargon and discoveries of observational cosmology is also essential for understanding the details.

Some of the text is taken up with re-enacting past battles with a diverse collection of critics ranging from Nobel laureates to cranks. They are variously scolded as "emotionally driven" and "religiously motivated", and are even characterised, in one illustration, as a flock of geese. Although much of this is pejorative and anecdotal and many of the targets are, sadly, no longer able to give their version of events, the published record is sufficient. Much of the early case against steady-state cosmology was flawed, but from the mid-1960s, two arguments against it have seemed particularly compelling to almost all practising astrophysicists and have resulted in the steady-state theory having few adherents beyond the authors.

The first argument involves microwave background radiation, discovered in 1965 by Arno Penzias and Robert Wilson. This is now measured to have a "thermal" spectrum to better than one part in 10,000, which means that it emerged from a drab and featureless environment where all components shared a common temperature. This is a perfect description of the 300,000-year-old universe at the time when it became transparent, according to orthodox cosmology, and is not at all a characterisation of the modern, hurly-burly universe with its motley collection of stars, supernovae and active galaxies.

The second argument involves quasars. Conventionally, quasars are accreting, massive black holes in the nuclei of galaxies and their "redshifts" are believed to be due to the expansion of the universe. Consequently, most quasars are quite distant and observed when the universe was much younger. They were more than a thousand times more plentiful when the universe was roughly a quarter of its present age, in clear violation of the simple, steady-state view.

In addition, there are several arguments that directly support the big bang model. Perhaps the two most telling are its successful prediction of the number of families of elementary particles in order to account self-consistently for the synthesis of the light elements, and the successful measurement of the long-anticipated, tiny fluctuations in the temperature of the microwave background - especially those on an angular scale of one degree. These show that space really is flat and are consistent with inflation (though they do not prove it).

To their credit, the authors discuss all these issues and then set down, with commendable specificity, their alternative interpretations. They assert that the microwave background is starlight that has been thermalised by graphite and iron "whiskers" formed and ejected by supernovae. They conclude that for this to have been possible, it is necessary to introduce a more complicated "quasi-steady-state model" where periodic cycles of expansion and contraction are superimposed on the overall expansion so that thermalisation occurs during maximum compression. At this point, the theory is starting to approach the orthodox big bang, albeit with the crucial difference that there was no "early" universe and no physical singularity in the past or, incidentally, in black holes - which the authors clearly regard as a virtue. Hoyle et al also argues that quasars are the site of mass creation in a manner that can contribute a variable, non-cosmological component to their measured redshifts. The highly contentious evidence for this effect and the associated claim that quasars can be expelled from galaxies is presented in some detail.

I hope that this book is not completely ignored by younger cosmologists because it will help them to understand how Hoyle and others started to consider some bold and relevant cosmological ideas long before anyone else and to give credit where it is due. I also trust that they will strip away the bluster and take to heart some serious concerns about hyperbole and uncritical thinking in the methodology of modern cosmology. Finally, I hope that some of them will take the time to examine objectively and independently, as many of us believe we have already done, the observational evidence for the two most radical and addressable notions expounded in this book, namely that the microwave background is not a relic of the big bang, but, instead, re-processed starlight and that, second, quasars are not accreting, massive black holes in the nuclei of ordinary galaxies but creation sites that can contribute a large, non-cosmological component to their measured redshifts. It is symptomatic of the excitement and possibilities inherent in contemporary cosmology that we do not know what new ideas this examination might stimulate.

Roger Blandford is professor of theoretical astrophysics, California Institute of Technology, Pasadena, United States.