Einstein's Clocks, Poincare's Maps: Empires of Time

Primitive humans had only two times, light time for living and dark time for hiding. The development of agriculture demanded the refinement of a seasonal calendar so that the crops could be planted at the appropriate time. This was only the first step in the simultaneous development of more accurate clocks and advanced technology. The dangers of navigating the seas required the precise computation of longitude, which required an accurate clock and the determination of a point of zero longitude. A growing network of railroad tracks with multiple trains using them required that the trains have highly synchronized timepieces. A difference of less than a minute could lead to a collision and there was several crashes due to such differences. These problems led to an international effort to establish a universal time and an international agreement as to the placement of zero longitude. Henri Poincare was a leader of the movement to establish these standards and in this book the historical background explaining why they were needed is given. There were also many social and political forces that required many compromises between those who were pushing their nationalist agenda. The story of how the logical solution of zero longitude was set at Greenwich is a story of how international agreements can be reached. The most interesting story is how the requirements of synchronized time led Albert Einstein to his theory of relativity. His primary conclusion was that it is impossible. The finite and fixed speed of light meant that synchronization could only be done within the bounds of that restriction. It is amazing to consider all of the consequences of this simple premise and those consequences are explained in detail. The most fascinating statistic in the book deals with the need for a relativistic correction in the Global Positions System (GPS) signals. This satellite system allows for the pinpointing of a position on the earth within a few feet. If no relativistic corrections were made, then after only a single day, the error in the GPS system would be on the order of six miles. This is a book on a very specific and necessary area of technological advancement. One measure of the improvement in technology is the precision of our clocks and from this book, you can see why it is important and in many ways necessary. The primary downside is the last chapter, where about twenty pages could have been deleted without any loss of critical information.

Einstein and Poincare were two inventors who made parallel attempts to harness time and helped create the science of relativity; but no single study has previously drawn such close links between the efforts of the young German physicist Einstein and the mathematician Poincare. Peter Galison's Einstein's Clocks, Poincare's Maps expertly examines the achievements and details of each, and in doing so incorporats new information drawn from forgotten patents, rare photos, and archived materials to chart a little-known but inherently fascinating race toward a theory of time. An important addition to school and community library History of Science collections, Einstein's Clocks, Poincare's Maps is an exciting, intriguing and enthusiastically recommended coverage.

It is so easy to tell when one thing happens simultaneously with another. You just see them both happen at the same time, simple. But let's say you are very sensitive to the speed of light, so sensitive that you can tell the difference in the interval between light coming from five miles away or ten miles away. Imagine yourself on a mountain and you see simultaneous lightning strikes on mountains that are both five miles away from you. You see the light from both at the same time; simultaneity is easy to spot. But now imagine the lightning hits simultaneously a mountain five miles away and another ten miles away. You now see one lightning strike well before the other. Where did the simultaneity go? It has suddenly gotten complicated and elusive. _Einstein's Clocks, Poincaré's Maps: Empires of Time_ by Peter Galison (Norton) is the story of what happened when two quite different thinkers contemplated the problem of simultaneity, and also of how people have done their best to promulgate an increasingly accurate time within their cities, countries, and the world.Quite famously, the young Albert Einstein was a mere minor bureaucrat in the Patent Office in Berne starting in 1902. Galison shows that time synchronization had to be on his mind because some of the patents he examined were for gadgets to help keep clocks in synchrony. Synchronized clocks were becoming increasingly important, for keeping trains from hitting each other, and then to keep microseconds from interfering with mapmaking. Poincaré was President of France's Board of Longitude, and synchrony was vital to him as he sent time-signals to cartographers in, say, South America. If the sent time was off due to cable delivery, the map might be half a kilometer in error. Poincaré's contemplations of synchrony led him to a mathematical concept of relativity that preceded Einstein's. Poincaré, however, didn't take the leap to eliminate the ether as Einstein did.This is not a book to explain relativity. It is a broad history of modern timekeeping, and since Poincaré is a relatively obscure figure, his polymathic additions to different fields of knowledge will be astonishing to most readers. It especially concentrates on how there was a complex historic interplay between theories and mechanisms, abstract and concrete inventions, that brought our current understanding of relativity about. It is a stimulating work, sometimes not easy to get through and certainly not easy to summarize. But there are intriguing insights about the two personalities involved, and fascinating explanations of the give and take in mathematics, engineering, philosophy, and physics eventually that allowed relativity to be understood.

In this book, Peter Galison attempts to show that scientists and mathematicians, no matter how brilliant, do not work in a vacuum. The focus is more on Henri Poincare than Albert Einstein, although Einstein is certainly not slighted. It's just that Mr. Galison feels, at least as far as the general public is concerned, Poincare has been "slighted,"....and this book, in part, is an attempt to redress the situation. It is easy to think of mathematicians and physicists as being disconnected from the "real world." Mr. Galison wants to show us, however, that they are influenced heavily by their colleagues in the scientific community and, more generally, by the culture they are part of. Thus, Poincare (president of the French Bureau of Longitude) was a creature of his times: he was "formed" by his education at the Ecole Polytechnique, with its emphasis on combining theory with practice. He was a man who "networked," and constantly exchanged ideas with fellow mathematicians and scientists. As a Frenchman, he shared in the humiliation of the French defeat at the hands of the Prussians in the war of 1870. Thus, it was important for France to lead the way in the longitudinal mapping of the planet (which required the synchronization of clocks across great distances). This longitudinal mapping was important for war and peace (for moving armies and navies...and oceangoing commerce). Synchronized clocks, even apart from their relationship to longitude, were also important for other reasons- such as for regulating railroad schedules. Mr. Galison's point: time was in the air and, since the outlook was global, there was an understanding that time was relative rather than absolute. Mr. Galison is not trying to say that Poincare "invented" the Theory of Special Relativity. What he is trying to say is that the obsession with time was "in the ether." Einstein, in Switzerland, was not immune to these influences. Which brings us to, for me, anyway, the most interesting part of the book - the relationship between Einstein's work at the Bern patent office (both the specifics and the methodology). People were constantly trying to come up with better ways of synchronizing clocks, and Einstein saw many of these patent applications. Also, it was his job to evaluate patent applications. The patent application (amongst other things) has to show that you've come up with something original, and it also has to show clearly how the invention will work. Mr. Galison makes a convincing argument that Einstein's job, at the very least, kept him thinking about the synchronization (and, hence, the relativity) of time. Even more interesting, in his 1905 paper on Special Relativity, Einstein did not use footnotes or make references to other scientists. Mr. Galison speculates: was this arrogance on Einstein's part, or was he influenced by his work at the patent office? In other words, it wouldn't help your case if, in a patent application, you showed how your idea was based on other ideas. Y