Einstein by Walter Isaacson

had inaugurated an urban time network of electrically synchronized clocks in 1890, and a decade later, by the time Einstein had arrived, finding ways to make them more accurate and coordinate them with clocks in other cities became a Swiss passion.
    In addition, Einstein’s chief duty at the patent office, in partnership with Besso, was evaluating electromechanical devices. This included a flood of applications for ways to synchronize clocks by using electric signals. From 1901 to 1904, Galison notes, there were twenty-eight such patents issued in Bern.
    One of them, for example, was called “Installation with Central Clock for Indicating the Time Simultaneously in Several Places Separated from One Another.” A similar application arrived on April 25, just three weeks before Einstein had his breakthrough conversation with Besso; it involved a clock with an electromagnetically controlled pendulum that could be coordinated with another such clock through an electric signal. What these applications had in common was that they used signals that traveled at the speed of light. 49
    We should be careful not to overemphasize the role played by the technological backdrop of the patent office. Although clocks are part of Einstein’s description of his theory, his point is about the difficulties that observers
in relative motion
have in using light signals to synchronize them, something that was not an issue for the patent applicants. 50
    Nevertheless, it is interesting to note that almost the entire first two sections of his relativity paper deal directly and in vivid practical detail (in a manner so different from the writings of, say, Lorentz and Maxwell) with the two real-world technological phenomena he knew best. He writes about the generation of “electric currents of the samemagnitude” due to the “equality of relative motion” of coils and magnets, and the use of “a light signal” to make sure that “two clocks are synchronous.”
    As Einstein himself stated, his time in the patent office “stimulated me to see the physical ramifications of theoretical concepts.” 51 And Alexander Moszkowski, who compiled a book in 1921 based on conversations with Einstein, noted that Einstein believed there was “a definite connection between the knowledge acquired at the patent office and the theoretical results.” 52
“On the Electrodynamics of Moving Bodies”
     
    Now let’s look at how Einstein articulated all of this in the famous paper that the
Annalen der Physik
received on June 30, 1905. For all its momentous import, it may be one of the most spunky and enjoyable papers in all of science. Most of its insights are conveyed in words and vivid thought experiments, rather than in complex equations. There is some math involved, but it is mainly what a good high school senior could comprehend. “The whole paper is a testament to the power of simple language to convey deep and powerfully disturbing ideas,” says the science writer Dennis Overbye. 53
    The paper starts with the “asymmetry” that a magnet and wire loop induce an electric current based only on their relative motion to one another, but since the days of Faraday there had been two different theoretical explanations for the current produced depending on whether it was the magnet or the loop that was in motion. 54 “The observable phenomenon here depends only on the relative motion of the conductor and the magnet,” Einstein writes, “whereas the customary view draws a sharp distinction between the two cases in which either the one or the other of these bodies is in motion.” 55
    The distinction between the two cases was based on the belief, which most scientists still held, that there was such a thing as a state of “rest” with respect to the ether. But the magnet-and-coil example, along with every observation made on light, “suggest that the phenomena of electrodynamics as well as of mechanics possess no properties corresponding to the idea of