This is possibly the best book I have ever read on the history of science, and if you're interested in the subject I recommend it very highly. Professor Kragh sets out to describe the revolution in our concept of the universe that happened between 1915 and 1970. It is every bit as dramatic as the Copernican revolution 400 years earlier, and when he published it (1995) several of the key players were still alive; he talked to most of them, and one (Bondi) is quoted on the back as expressing his appreciation. This is a classy piece of work. The two theories in the title are the Big Bang, which eventually won, and the Steady State Theory, which mounted a spirited challenge but lost. A large part of the book is about the rivalry between these two theories, and describes how the scientific community eventually decided in favor of the Big Bang. Kragh appears to have read just about every relevant book and paper published during the period, and has done a phenomenal job of organizing this huge mass of material. I am sure there was a temptation to write a bloated thousand-page tome, but he has managed to cut it down to 390 pages of main text plus a hundred or so of end notes and bibliography, which feels just about right. He never shows off his scholarship, but concentrates on the main question: how did we reach the current state of affairs, where nearly everyone in the scientific world believes in the Big Bang? As a result, the book is engaging and highly readable. I got through it in a few days.
What I found most impressive is the way Kragh balances five different perspectives: science, history, sociology, philosophy and religion. He is in no way afraid of the science, which he clearly understands in great depth, and he presents equations and graphs whenever they are necessary to support the details of the argument. Although my own understanding of the other subjects is not really sufficient to give a critical appraisal, I found his presentation compelling. As a historian, he comes across as objective and even-handed. He has no obvious axe to grind, and tries hard to help the reader see things as they appeared at the time, not in the light of what came later. As he says, it's all too easy to look at an idea which turned out to be correct, and present it as an amazing flash of insight: often, it's more accurate to call it a lucky piece of speculation. The way he distinguishes between the two is interesting and thought-provoking. In particular, he dismisses claims that Alexander Friedmann should be considered the true originator of the Big Bang theory. Friedmann's 1922 paper was indeed the first thing written on the subject, but Kragh argues that Friedmann was just doing a piece of abstract mathematics, and never seriously considered whether it had anything to do with the real world. It so happened that it did, but we can only see that from our perspective.
As someone who works in science, I have often wished that more people would write about its sociology from the inside, but they so rarely do; Smolin's The Trouble with Physics
is a fine exception, though it's hard to call Smolin impartial. Kragh comes across as a dispassionate referee, despite the fact that the debate was often highly emotional. One of the best passages occurs near the end, when the Steady State theory is starting to come apart. I had not understood that the thing which contributed most to sinking it was the non-uniform distribution of radio galaxies, as discovered by Ryle's Cambridge group during the late 50s. It all came down to the slope of a certain curve: if the gradient was less than 1.5, the Steady State theory was okay, but if it was higher then the theory was dead. In their second survey (2C), the Cambridge group found a value of 3.0, but it turned out that the results were unstable, and could not be replicated. The third survey (3C) gave a revised value of 1.8. When the results were presented at a conference, Bondi, one of the main champions of the Steady State, made an ironic comment: the number had now dropped from 3.0 to 1.8, so were there grounds for hoping that it might progress to 1.5 in the next edition? Ryle's group had put in years of work in obtaining this number, and the reputations of both groups were largely dependent on what happened. When Bondi asked his question, Ryle lost his temper completely, to the amazement of the audience; one of them said he had never seen such an open display of anger in the 30 years he had been in the field. But it turned out that the 1.8 value was solid, and Ryle later was awarded the Nobel Prize, while Bondi quit the field.
And, last but not least, philosophy and religion. One of the most extraordinary aspects of the whole affair was the sharp polarization in this area: the Big Bang theory was to a large extent the work of Georges Lemaître, a Catholic priest, while the leader of the Steady State side, Fred Hoyle, was a militant atheist. So many opportunities to sensationalize the narrative! Kragh examines the evidence in his calm way, and comes to a conclusion that is almost too reassuringly prosaic: even if people's religious or anti-religious beliefs predisposed them to choose their side accordingly, the debate was conducted on purely scientific grounds. Though an interesting footnote is that the Soviet Union, under Stalin, decided all cosmology was bourgeois, so Russian scientists hardly got a chance to contribute.
Such an amazing story, and such a great book! I must read some more Kragh.