HISTORY OF FIBER OPTICS
This week’s History of Fiber Optics is taken from George Gilder’s book, Telecosm.: In 1887, two American experimenters, Albert Michelson and Ed Morley, tested the idea that earth’s orbital velocity would affect the speed of light. In an ingenious experiment, they split a beam of light and sent it in perpendicular directions to two identical mirrors. When the split beams bounced back, they converged in a device—called an interferometer—invented by Michelson specifically for the purpose of this experiment. If the speed of light was affected by the earth’s rotation through the ether (empty space)-–as most scientists of that day thought it would be—then the beam moving parallel to earth’s orbit would move faster than the one traveling perpendicular. The expected result—a shift of some forty percent of the chosen lights wavelength—would produce an identifiable interference pattern at the spot where the two beams converged. Meticulous scientists, Michelson and Morley performed the experiment twice, rotating the whole apparatus 90 degrees after the first attempt, to compensate for possible discrepancies between the two light paths. But the results showed absolutely no impact from the earth’s orbital velocity. In 1958, laser inventor Charles H. Townes confirmed the Michelson—Morley results at Bell Labs using high-frequency radio waves which is but another form of light.
By defining all electromagnetic radiation by a ratio that involved this velocity, c, Maxwell had made the light-speed limit inherent in the phenomenon itself. Nuclear experiments in 1937, using Einstein’s canonical 1905 equation, e=mc squared, further established the total autonomy of light. The experiments compared the masses (m) before and after a nuclear reaction and measured the amount of energy (e) released in the reactor. C squared remained and it equaled the immense ratio of the energy over mass. Since both the masses and energies were measurable or known quantities, the equation could be solved for c, assumed to be unknown. That calculation, involving no conventional speed measurements at all, yielded the velocity of light to an accuracy of half a percent. Light speed is an absolute and it is intrinsic to the resonant fabric of the known universe.
In telecommunications, the speed of light provides crucial stability. If its speed changed as the earth moved, electrons moving inside a computer would have different velocities, depending on how the device was orientated to our planet, or in which direction they were traveling inside the machine. Michelson—Morley’s error factor of one in ten thousand might not seem like much, but it is a hundred times greater than the modulation in most microwave-based communications systems. Analog TV is unusable without signal-to-noise ratios of 50 decibels—one hundred thousand to one. Shifting the speed of light would skew the nanometer channels of wavelength division multiplexing many colors of light down a single fiber thread. It would disrupt the machines used to scribe patterns smaller than the wavelength of ultraviolet light on microchips. It would confound the global positioning satellites that guide your Never-Lost-Hertz rental car. And it would not help those cruise missiles racing across enemy skies find their target. By the beginning of the twentieth century, Michelson-Morley had plunged conventional thinking about the speed of light into a state of prolonged crisis. Maxwell had calculated it as a constant half a century earlier. But that idea did not conform to the consensus (including Maxwell’s own belief) that the earth moved through fixed ether, and that light speed therefore had to be variable, dependent on the movement of its source. Then there was Newton’s ancient principle of relativity—that it is impossible to measure an object’s velocity except by reference to some other object. Could light be the absolute exception?
To be continued…
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