Happy Birthday James Clerk Maxwell

jim-stewart Jim Stewart June 13, 2018
Are you reading this over a Wi-Fi connection? Maybe while listening to music with Bluetooth earbuds? Or perhaps you are in a barbaric restaurant without Wi-Fi, so you are using the LTE network to surf the web while FM radio plays in the background. All examples of communications technologies that use radio waves. Nooo! Let’s not call them "radio waves." Let’s use their original name: Maxwellian waves! June 13th, 1831, is the birthday of Scottish mathematician and physicist James Clerk Maxwell, and without him we would all have very different jobs. Maxwell predicted the existence of radio waves—or at least generalized electromagnetic waves. Maxwell was undeniably brilliant. He began boarding school at age 10, and although from a well-to-do family, with his thick accent and home-made clothes, he reportedly came across as a bit of a hick. His interests were wide-ranging and he did not pay much attention to his exams, so at first he did not shine as a scholar. That is, until at 14 when his first scientific paper­—on ellipses and mathematical curves—was presented to the Royal Society of Edinburgh by a university professor. At 25 he became Professor of Natural Philosophy at Marischal College, Aberdeen. While there, he mathematically proved that Saturn’s rings could not be solid or liquid, but must be a collection of small particles, or “brickbats.” Now, no matter how brilliant, no scientist stands on his own. Michael Faraday, building on the work of Hans Christian Orsted, Carl Gauss, Andre Ampere, Alessandro Volta—note those last names—and others, had already demonstrated that electricity and magnetism were related phenomena. What Maxwell did was to take everything known about electricity and magnetism, clean it up and unify all the equations. Maxwell published his results in March 1861 as 20 equations that later scientists (Heinrich Hertz, Oliver Heaviside, etc.) reduced to four using vectors and partial differential equations. There is no need to stress about understanding the math—truth be told, your humble author has forgotten it himself. (College was a while ago.) But they say two real things in layman’s terms: 1) An electric current generates a magnetic field, and  2) A changing magnetic field generates an electric current. Now that was brilliant work. Ever pick up Discover Magazine and read about the quest for the “Unified Field Theory?” The above is the unified field theory of 19th century physics. Brilliant work, worthy of a Nobel Prize (except that the first Nobels were not handed out until 1901). But that’s not the whole story. Once he got to this point, Maxwell played around with these equations. He wondered what would happen under simplified conditions in which a lot of the terms would go to zero. That is, how does an electromagnetic field operate in free space rather than when confined to a wire? Here I picture Maxwell, hunched over his desk, pencil in one hand, the other pushing his hair back from his forehead in the universal physicist's gesture of deep concentration, playing with these equations, even though he has already done extraordinary work and deserves some time off. He sits there, scratches out terms that go to zero, solves for a couple of variables, combines equations, simplifies terms… and then he notices something. He now has a single equation that looks like the mathematical description of a wave. Could electricity and magnetism make a wave that travels through space? More than that, a wave equation has a term for the velocity, and in Maxwell’s resulting equation, the velocity term is a combination of the universal magnetic constant (μ0 ‘mu sub-zero’), and the universal electrical constant (ε0 ‘epsilon sub-zero’); values known at the time from experimentation. Maxwell looks them up (or, being Maxwell, he probably has them memorized to 10 places), calculates the velocity of these waves—and gets a value that matches the known speed of light! Now think about that. Maxwell has just cleaned up a whole major field of physics, uniting two physical phenomena into aspects of one thing, and he has just discovered that a third—supposedly completely unrelated—phenomenon might also be the same thing! Could light be an electromagnetic wave!? Amazing work, an amazing moment, and I get emotional just thinking about it. After all, that might be the greatest thought ever contained by a human brain! Excuse me, someone is cutting onions nearby. Of course, things didn’t stop with Maxwell. It may be his birthday, but scientists don’t stand alone. The above may be one of the greatest examples of a theoretical physicist producing a crazy-bleep theory, but history needs an experimental physicist to test it. Enter Heinrich Hertz. Hertz had considered testing Maxwell’s theory for his doctoral thesis at the University of Berlin, but decided it was too difficult. Later, as a professor at the University of Karlsruhe, while experimenting with an early kind of capacitor (called a Leyden jar) and a pair of coiled conductors in 1886, he observed that discharging the capacitor into one coil produced a spark on the other, unconnected coil. Building on this observation over a three-year period, Hertz used spark gap generators to create and detect EM waves, measure their speed, wavelength and polarization; thus validating everything Maxwell’s equations predicted. https://www.youtube.com/watch?v=UN37QEmW_ns About his experiments, Hertz said: "It's of no use whatsoever[...] this is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there." Asked if there were any practical applications, his reply was, "Nothing, I guess." Enter applied physics and engineering, in the person of Guglielmo Marconi. Marconi was an Italian aristocrat on his father’s side, and a great-grandson of John Jameson of Irish whiskey fame on his mother’s side. As a teenager in the 1890s, he utilized Hertz' experiments to build "wireless telegraphy" equipment in the attic of his home in Italy. First, he built a system that could wirelessly ring a bell across a room, then transmit Morse Code half a mile, then over two miles. In 1896, Marconi and his mother moved to England, where there was more interest in his experiments. By early 1899, Marconi’s technology provided communications between the South Foreland Lighthouse in Dover and the East Goodwin Lightship (floating lighthouse) 12 miles away, and in March, a life-saving signal was sent, summoning help for the run-aground merchant vessel Elbe. All of which brings us to the twentieth century, and enough history for today. So on this June 13th, take a moment to appreciate just how pervasive wireless communications have become in our lives. Maybe think about lifting a glass of your preferred beverage to the memory of a 187-year-old Scottish university professor who made it all possible. We stand on the shoulders of giants, and James Clerk Maxwell was one of the tallest.

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Jim Stewart

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