Einstein's Clocks, Poincare's Maps: Empires of Time (review)

At the beginning of the twentieth century, Albert Einstein identified the key to transforming how we understand the dynamic universe. The way to that understanding, he believed, lay in a new way to think about time. With the publication of his paper on the theory of special relativity in 1905, Einstein abandoned the notion of the ether, accepted the speed of light as a constant, and overturned Newton's definition of a single uniform and unidirectional time in favor of a universe that allowed multiple times relative to moving observers. The paper furnished the crucial road map for a new physics and the guide to new notions about time, space, and simultaneity.

Primary sources about the route to relativity are few, and historical interpretations are many. (For an introduction to the historiography, see David Cassidy, "Understanding the History of Special Relativity," Historical Studies in the Physical and Biological Sciences 16, no. 1 [1986]: 177-95, and his reading list at http://www.aip.org/history/einstein/einlinks.htm.) It is likely that the history will never be recounted in quite the same way again now that Peter Galison has written this book. Like Einstein in search of a unifying theory, Galison suggests a way to connect seemingly separate "empires of time" in the realms of physics, philosophy, and the material world's standardized time zones and ubiquitous electrically synchronized clocks. He joins those who argue that relativity theory originated not just in pure thought but also in real-world experience.

Galison's easy familiarity with turn-of-the-century physicists is evident, although uninitiated readers may lose their way from time to time in his descriptions of their work. The book's strongest parts are Galison's absorbing portraits of the title figures and his analysis of how Einstein's ideas about relativity prevailed and those of French mathematician Henri Poincaré did not.

The reader meets Einstein as a brash youngster working in the Swiss patent office in Bern. Far from the iconic ivory-tower genius of his later years, this Einstein is immersed in the electromagnetic technologies of his day, a "tinkerer, souping up homebuilt instruments in his Kramgasse apartment, . . . riveted by the design of machines and the analysis of patents" (p. 46). And, most critical for Galison's argument about Einstein's ideas of simultaneity, this Einstein knows Bern's rail, telegraph, and electrically synchronized clock network. The clocks of the book's title occupy key positions both in Einstein's relativity thought experiments and in his street scene. Galison imagines that Einstein sees clocks at the train station, on his route from home to work, all around him in Bern, a clock-conscious city in a country passionate about watches. Readers hoping to learn about turn-of-the-century electrically synchronized clocks and their repeated failure, by the way, will be disappointed. The book claims that such clocks were an important part of the landscape, but engages with their technical and social history only lightly.

In a sympathetic portrait of Poincaré, Galison builds a convincing case that the Sorbonne professor was no isolated academic either. He was, instead, engaged in practical concerns aimed at furthering the ends of the French empire. Early in his career he was an expert mining engineer. Later he headed the Bureau des Longitudes, where he focused on matters of earthly time and space. Poincaré's maps are more than eponymous mathematical constructs in topology. They are the material results of the bureau's scientific cartography that helped claim and maintain distant colonies and synchronized them with the mother country.

Galison offers an original and provocative interpretation of the route to relativity in an extended account of international time reform at the turn of the twentieth century. Time reformers in Europe and North America coordinated their efforts to introduce global time zones and synchronize the world with time signals sent telegraphically and by radio. Readers will find, for example, a...