Abstract
In 1954, The British Journal for the Philosophy of Science featured a discussion between Gerald Whitrow and Hermann Bondi under the title “Is Physical Cosmology a Science?,” a question which at the time was more than just rhetorical. Seventeen years later it was answered with a resounding yes, namely, with Princeton University Press’s publication of Physical Cosmology, the first time that the term appeared in the title of a textbook. The author was the 35-year-old Canadian-American physicist Jim Peebles, who 5 years earlier had discovered, together with his mentor Robert Dicke, that the cosmic microwave background radiation is a fossil of the big bang. Since then, P.J.E. (Philip James Edward) Peebles has contributed importantly to a wide range of topics in theoretical cosmology, including structure formation, dark matter, dark energy and primordial nucleosynthesis. His lifelong work in cosmology was crowned in 2019, when he received one half Nobel Prize for “contributions to our understanding of the evolution of the universe and Earth’s place in the cosmos.”
The focus of Cosmology’s Century is on post-1960 theories and observations of the universe, but it also examines in some detail earlier developments such as the steady-state theory – “a magnificent philosophical construction” (p. 351) – and George Gamow’s important but curiously uninfluential work on the hot big bang. The book explains carefully and critically the relationship between the old big bang theory building on “Gamow’s intuitive genius” (p. 347) and the new one which emerged in 1965 as a result of the discovery of the cosmic microwave background. The new picture of the universe was principally due to Dicke’s research group in Princeton, but as Peebles makes clear, very important contributions were also, and largely independently, made by Yakov Zeldovich and his group in the Soviet Union.
A significant part of the book deals with Peeble’s involvement in the development, and yet it is, first of all, an objective account of cosmological research and not a scientific autobiography. The structure of the book is not strictly chronological, as one might expect, but rather subject-oriented with, for example, a long chapter on dark matter following an equally long chapter on cosmic structure formation. This textbook-like organization, together with a relatively high technical level, will probably appeal more to historically interested physicists and astronomers than to historians of science. In this respect, the book has features in common with Malcolm Longair’s The Cosmic Century: A History of Astrophysics and Cosmology published by Cambridge University Press in 2006.
As witnessed by its 45-page bibliography, Peebles’ book is based on exhaustive historical documentation. It makes excellent use of both primary and secondary sources, including his own recollections and personal communications from some of his colleagues which add valuable information that cannot be found elsewhere. However, the historical perspective is largely limited to the technical and scientific development, which Peebles describes in fascinating and insightful details. As indicated by the subtitle, the book is an inside history and not an outside or contextual history of modern cosmology. This is indirectly reflected in the bibliography which comprises more than 1000 references of which fewer than a handful are written by historians of science. The book has almost nothing to say about the history of cosmology in its broader sense, including such aspects as its public appeal, its social and communicative structure, and its ideological and philosophical implications. Some of the more general perspectives are taken up in the final chapter, which is reflective and interesting if also, in my view, disappointingly narrow. The chapter includes a section with the provocative title “The Social Construction of Science.” Although Peebles is definitely not a social constructivist in the sense of philosophy and sociology of science, he labels cosmology in the 1920s as a “social construction” which eventually, with new observations and methods of testing, was turned into an “empirical construction.”
Cosmology’s Century is primarily written with a scientific audience in mind, but it is also of great interest, even indispensable, for the small community of historians of modern astrophysics and cosmology. As Peebles notes in the preface, “It is generally acknowledged that in natural science, we take poor care of our history” (p. viii). This may be true in general, but with Cosmology’s Century it is no longer the case for modern cosmology. Its limitations apart, the book is by far the most authoritative and detailed account of how cosmology, a century after Einstein’s pioneering theory of the universe of 1917, became an advanced science in the form of the present standard cosmological model.