Today the name of Einstein is known to almost everybody, the name of Poincaré to almost nobody. A hundred years ago the opposite was true. Then, Albert Einstein was a newly appointed technical expert, third class, examining patent applications in the Swiss patent office in Bern, having failed in his efforts to find an academic job, while Henri Poincaré was one of the leading figures of the French scientific establishment, famous not only as a great scientist but as the author of popular books that were translated into many languages and kept the public informed about the dramatic progress of science during the early years of the twentieth century. A hundred years ago, Einstein and Poincaré were both working hard at one of the central problems of science, trying to find a correct theory to describe how fast particles behave in electric and magnetic fields. Poincaré had published several papers on the subject which Einstein may or may not have read. Einstein had published nothing.
Two years later, in 1905, Poincaré and Einstein simultaneously arrived at a solution to the problem. Poincaré presented a summary of his results to the French Academy of Sciences in Paris, and in the same month Einstein mailed his classic paper, “Electrodynamics of Moving Bodies,” to the German journal Annalen der Physik. The two versions of the solution were in substance almost identical. Both were based on the principle of relativity, which says that the laws of nature are the same for a moving observer as they are for an observer standing still. Both agreed with the experimentally observed behavior of fast particles, and made the same predictions for the results of future experiments. How then did it happen that Einstein became world-famous as the discoverer of relativity, while Poincaré did not? Poincaré’s lasting fame, such as it is, derives from his discoveries in other areas of science and not from his work on relativity. Is the verdict of posterity, giving all the credit for relativity to Einstein and none to Poincaré, fair or unfair? I will return to these questions later.
Peter Galison is a historian and not a judge. His purpose is to understand the way in which Poincaré and Einstein arrived at their insights, not to hand out praise or blame. His book is an extended double portrait, describing their lives and times in detail. At the beginning, he complains of the unequal treatment given to them by biographers: “There are, to be sure, too many biographies of Einstein and not enough of Poincaré.” Poincaré was a great man who lived a full and many-sided life, and he deserves at least a fraction of the attention that has been lavished on Einstein. For readers who may be interested in learning more about Poincaré, I recommend a short biography by Benjamin Yandell that Galison does not mention. Yandell’s book, The Honors Class: Hilbert’s Problems and Their Solvers,* is a collection of biographies of mathematicians who solved a famous list of twenty-three problems propounded by David Hilbert at the International Congress of Mathematicians in Paris in 1900. Poincaré solved problem number 22. The Poincaré biography in Yandell’s book is one of the best. It gives us in thirty pages a vivid picture of Poincaré’s life as a mathematician, and overlaps very little with Galison’s account.
Galison’s book does not contain a single equation. Anybody with an interest in history can read it. The stories that it tells are mostly about the applications of science and not about science itself. The applications are things that everybody can understand, maps in the case of Poincaré, clocks in the case of Einstein. Poincaré and Einstein were both deeply involved in the practical world of electrical communication and machines at the same time as they were working out the theory of relativity. The scientific theories that emerged from their practical concerns are described briefly, without any mathematical or technical jargon. The book consists of six chapters, four long chapters in the middle and two short chapters at the beginning and the end. The two short chapters set the stage and summarize the conclusions. The little that is said about the details of the theory of relativity is mostly contained in the two short chapters. The main conclusion is that, in the events that led to the discovery of the theory, philosophical speculation and technological invention were inextricably mixed.
The four long chapters consist of a collection of stories, describing how electricity transformed the world in the second half of the nineteenth century. Here is a typical story. A political battle was fought in Hartford, Connecticut, in 1880, to decide whether the trains in Connecticut should run on Boston time or New York time. The battle was fought between the Harvard astronomer Leonard Waldo and the New York to Hartford railroad. Waldo was not only an astronomer but also an entrepreneur. His observatory ran a business, selling accurate time signals that were distributed to customers by electric telegraph. The customers were railroads and city fire departments, manufacturers and retailers of clocks and watches, and private citizens who possessed fine watches and wished to check their accuracy. Waldo made a big pitch to the Hartford city council, emphasizing the superior precision of Boston time. But the New York to Hartford railroad ran on New York time and would not be moved. The railroad won the battle.
Another story tells how the United States led the world in adopting a unified system of time zones in 1883, with the times in neighboring zones differing by exactly one hour. This was another victory for the railroads. The crucial convention to decide the fate of the time-zone system was held in St. Louis, Missouri. The voting was measured not by the number of delegates voting but by the miles of railroad track that they represented. The final vote was 79,041 miles of track in favor and 1,714 miles opposed. After that, cities were compelled to set their clocks by railroad time and not by local time. Even New York City gave up its local time and set its clocks to astronomical time at longitude seventy-five west.
A third story tells how the French Bureau of Longitude established a commission in the year 1897 to extend the metric system to the measurement of time. The idea was to abolish the antiquated division of the day into hours, minutes, and seconds, and replace it by a division into tenths, thousandths, and hundred thousandths of a day. The new second would be a hundred thousandth of a day, and the new hour would be ten kiloseconds. The new units of time could then be handled as conveniently as grams and kilograms, meters and kilometers. To convert time from days to hours or minutes or seconds, we would only need to move a decimal point. We would no longer need to struggle with multiplications and divisions by twenty-four and sixty. This was a revival of a dream that was in the minds of the creators of the metric system at the time of the French Revolution a hundred years earlier. Some members of the Bureau of Longitude commission introduced a compromise proposal, retaining the old-fashioned hour as the basic unit of time and dividing it into hundredths and ten thousandths. Poincaré served as secretary of the commission and took its work very seriously, writing several of its reports. He was a fervent believer in a universal metric system. But he lost the battle. The rest of the world outside France gave no support to the commission’s proposals, and the French government was not prepared to go it alone. After three years of hard work, the commission was dissolved in 1900.
These stories, and many others, are told to illustrate Galison’s thesis that the coordination of time signals was a central concern of people and governments in the later part of the nineteenth century. So it was no accident that the coordination of time signals also has a central role in the theory of relativity. Poincaré and Einstein lived in a period of history when the transmission of time signals was a growth industry, and both of them were professionally involved in it. Poincaré worked for the Bureau of Longitude, which was responsible for the mapping of French territories around the globe. To make accurate maps, the bureau needed to determine accurate longitudes. To determine longitude at a remote place such as Dakar or Haiphong, it was necessary to compare the local time, obtained from local astronomical measurements, with Paris time, obtained by receiving an accurate time signal from Paris. The accuracy of maps therefore depended on the accuracy of long-distance transmission of time signals. The transmission of time signals, first by overland telegraph lines and undersea cables, and later by radio, was a difficult technical problem. Signals were attenuated by transmission losses and corrupted by ambient noise. The transmission introduced delays which had to be accurately calculated, so that Paris time could be correctly deduced from the observed time of reception of signals. The recording apparatus introduced other delays which had to be measured and compensated. The transmission of time signals with high accuracy required a mastery of both theory and practical engineering.
Poincaré was well versed in practice as well as theory. He started his professional career as a mining engineer, inspecting mines in the coal fields of northern France. One of his first jobs was to investigate a disastrous explosion that killed eighteen miners. He descended into the mine looking for clues while the corpses were still warm. He found a miner’s lamp which had a rectangular hole in its wire mesh, apparently caused by a blow from a pickax. The wire mesh, a device invented by Humphrey Davy sixty-five years earlier, prevents the flame inside the lamp from igniting explosive gases in the mine outside the lamp. The mesh allows air to pass through but stops flame from propagating from inside to outside. When the mesh was broken, the flame could propagate freely and all hell broke loose. Poincaré risked his life to discover what had happened, and wrote a report analyzing in detail the flow of gases in the mine.
Einstein grew up in a family of electrical engineers. His father and uncle ran a business in Munich, manufacturing and selling electrical measuring equipment. One of his uncle Jakob’s patents dealt with equipment for the electrical control of clocks. Einstein’s early familiarity with electrical machinery helped him to get his job at the Swiss patent office, and helped him to do the job well. As soon as he started work, he was confronted with numerous applications for patents concerned with electric clocks and with their coordination by distribution of electric time signals. In the year 1904, when the theory of relativity was in process of gestation, fourteen such patents were approved by the Bern office. The number of applications that were disapproved is not recorded.
A.K. Peters, 2002. ↩
A.K. Peters, 2002. ↩