Einstein's Clocks and Poincaré's Maps: Empires of Time

  • Peter Galison
W. W. Norton: 2003. 370 pp. $23.95 Sceptre: 2003. £14.99
Keeping time: the control room at the Rue du Télégraphe in Paris synchronized the city's clocks. Credit: MARY EVANS

The challenge of synchronizing clocks around the world, and accurately determining longitudes, required the construction of a great net of cables, often with considerable difficulty. With similar energy, scientists and politicians fought to establish the zero meridian and even the units of time (the French lost both contests, so Greenwich is the zero meridian and time was not decimalized). Peter Galison tells this tale in a tremendous yarn that takes up the largest of the three parts in his new book, Einstein's Clocks and Poincaré's Maps. Henri Poincaré was a prominent figure in these tumultuous events, and Galison argues convincingly, backed by a great deal of hitherto neglected information, that he was a leading product of his formative institution, the Ecole Polytechnique in Paris.

But what does this tell us about time? Newton had believed what most people involved in the creation of the global network of clocks believed, namely that the Universe is like a stage on which it makes sense to be able to say precisely when two separate events take place. The great struggle to create a single empire of time in which it was possible to say anywhere in the world what the time was (as recorded on a clock in London) was a move to put Newton's idea of time into operation. Observers in London, Paris and New York could all agree that it was, say, 17:00 (although local times might differ). This process is somewhat arbitrary, but the concept of time underpinning it is fundamentally Newton's, shorn, in Poincaré's view, of some illegitimate intuitions.

On this conception, a fast-moving observer can read off the time by simply looking at standardized clocks as he passes them. But that is not what can be done. Einstein's shattering insight into time is that Newton's universal time does not make sense. Observers in a state of constant relative motion with respect to each other do not keep the same time: their clocks beat at different rates.

By 1900, physicists knew that something was amiss in their theories. Prominent among them was Hendrik Lorentz, who in 1904 introduced a trick to resolve discrepancies in the theory of the moving electron. This was the idea of local time. Poincaré showed in 1905 that Lorentz's local time could be interpreted as the time kept by an imaginary clock moving with the electron as it beat against the ether. In the same way, lengths of objects were supposed to contract as they moved relative to the ether. By 1912, Poincaré had come close to accepting Einstein's theory, but he regarded it as a convention, to be accepted or rejected on utilitarian grounds, and never gave it the force that the iconoclastic younger man did.

This shift from one conception of time to another is the second theme of the book, and it is less successful. Galison would have us believe that empire time was radically different from newtonian time. He writes: “Newton's absolute, theological time had no place ... Engineering common time stood where God's absolute time had been,” but this seems unconvincing. Galison also downplays the details of the intense scientific debate, which was well described in Arthur I. Miller's Albert Einstein's Special Theory of Relativity (Addison-Wesley, 1980), in order to give salience to the technological and political factors he has identified. In so doing he pushes Poincaré and Einstein closer together than they were, stressing their involvement in the world of clocks and measurements, and diminishing the radical nature of Einstein's ideas.

Einstein is presented here as a serious and talented worker in the patent office. This is surely an improvement on his portrayal, sometimes fostered by Einstein himself, as an other-worldly academic, although Lewis Pyenson has already described Einstein as an enthusiastic worker in the patent office in The Young Einstein (Adam Hilger, 1985). Perhaps Einstein's daily working life contributed to his insistence on clocks and the measurement of time in his famous paper of 1905 in which he introduced special relativity. However, he is also described as a radical and an iconoclast. The inevitable question is then to decide what weight to attach to these different factors, and Galison refuses to address the matter.

Instead, he has written a methodological final chapter arguing for the inseparability of all the factors that he has introduced, from the grittiest to the most ethereal. He argues that Poincaré in particular was situated at the intersection of three arcs, namely developments in physics, telegraphy and philosophy. Einstein was likewise at a triple intersection, of a slightly different kind. We can accept that it is not easy to situate scientific discovery in a richly overlapping set of contexts, and that conclusions should be tentative, but by marginalizing the strictly scientific debate, the implication that the other arcs carry significant weight is allowed to slip through too easily. This matters greatly when discussing Poincaré, because it is often argued that his capacity to move between mathematics, physics and philosophy often weakened his insights into physics.

The logic of Galison's position is surely that, if empire time is by its nature different from newtonian time, then one might expect someone heavily committed to the establishment of empire time to differ from those habituated to newtonian time. Poincaré should differ from Lorentz, at least, and be closer to Einstein. If empire time was simply understood as being newtonian time put into practice, then Poincaré would resemble Lorentz and differ from Einstein, who believed that time had to be defined by means of clocks (and not merely captured).

Perhaps Poincaré's deep intellectual and political immersion in the creation of empire time with its global sense of simultaneity worked against him when he had the chance to reformulate time as Einstein did, and even to accept it afterwards as, steadily, his contemporaries did. But there are other possible explanations and such inferences are risky. Ultimately, the methodological sophistication in this book may not deliver what its author hopes, but the wealth of information it contains is surely stimulating.