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The idea of waves traveling through the air, and the possibility that they could be focused or bounced off surfaces, made inventors salivate. Some envisioned sending telegraph signals consisting of dots and dashes—short and long pulses—without the need for wires and poles. Such wireless communication between land and ships at sea, using what were at first called Hertzian waves, or aetheric waves, could be invaluable. (It took twenty years for the term radio waves to come into use.)
Early on, experimenters realized that various frequencies of radio waves have various propagation characteristics. Short waves can reflect off the ionosphere, more than fifty miles overhead, and bounce back to Earth in distant places, but locally they cannot bend, or diffract, around obstacles, such as mountains and buildings. Hence they are mainly useful in local, line-of-sight situations, such as (these days) when airplanes need to communicate with nearby control towers. Long waves, by contrast, can diffract around mountains and buildings and can more easily follow the curvature of the earth. Thus scientists realized that the radio spectrum offered a range of possibilities and that various wavelengths could be used for specific purposes.
It took just a few short years after Hertz’s 1888 discovery for entrepreneurs to start to recognize its technological potential. In 1892 the physicist William Crookes wrote about the possibilities of “wireless telegraphy” based on Hertzian waves. But a few other inventors, including Serbian American Nikola Tesla, disagreed, considering the waves useless for communication. Tesla mistakenly believed that this new form of invisible light, just like visible light, could not transmit farther than the observer’s line of sight; meaning that if the target was not in view the waves wouldn’t get there. (Tesla did initially experiment with radio waves, but never followed through because he was too preoccupied with attempts to send electricity through the air, which he regarded as a more promising and useful technology. Time proved him wrong on both counts.)
Inventors entering the business of wireless telegraphy soon were able to communicate across a range of several miles. Actually, in the United States, Tufts University professor Amos Dolbear had created a half-mile radio transmitter and receptor in 1882, before Hertz had officially discovered his waves. Unfortunately for Dolbear, he was too slow in applying for a patent and thus missed out on being credited with the invention of the radio. That honor went to the Italian Guglielmo Marconi, who in 1897, a mere nine years after the publication of Hertz’s paper, founded the Wireless Telegraph and Signal Company in Britain, which soon became the Marconi Company.
By 1899, wireless telegraph communications were crossing the English Channel; ever-larger antennas, stronger signals, and longer distances were announced almost monthly. Radio receivers, which started out as mere metal poles, began to use a more active receiving process that involved coherers. These were tubes containing two electrodes spaced a small distance apart with metal filings in between. When a radio wave reached the coherer, the metal particles clung together, or cohered, which diminished the high resistance of the device and allowed an electric current to flow through it. Thus hit with a radio signal, the current could activate a Morse code paper recorder and cause it to make a record of the signal. For their time, these coherers were marvelously high-tech. The invention of vacuum tubes made detecting radio waves far easier, and greatly extended their range—all this before the start of World War I.
By 1911, many ships were equipped with wireless telegraphs, and their range spanned hundreds of miles. Marconi’s device is what saved the lives of the Titanic’s seven hundred survivors when the sinking ship’s SOS call was received by the Carpathia, some fifty miles away.
Carrying voices or music—audio—required a different technique. Instead of discrete individual sparks, which was all that was necessary to produce Morse code, continuous radio waves needed to be sent and received. Modulations, or changes, in that continuous signal could convey the rapid-fire information contained in the human voice and the notes of the musical scale.
The first voice was wirelessly transmitted on June 3, 1900, by the Brazilian priest Roberto Landell de Moura. His first public experiment, in front of journalists in São Paulo, Brazil, broadcast his voice a distance of five miles across that city. He ultimately applied for and received three US patents after he took his equipment to Washington, DC.
The United States then woke up with a vengeance to this new technological wonder. After Westinghouse engineers invented the vacuum tube detector, radio-wave reception became far sharper. The first radio program broadcast, from Ocean Bluff–Brant Rock, Massachusetts, to ships at sea, took place on Christmas Eve in 1906. Using his brand-new synchronous rotary-spark transmitter, American inventor Reginald Fessenden played “O Holy Night” on the violin, then read a passage from the Bible.
The technology for this first-ever event was the same that powers AM radio broadcasts to this day. You see, a continuous wave is nice, but information—whether voice or music—requires pulsations, so the signal has to vary. Early radio waves could be stopped and started, which was fine for sending the dots and dashes of Morse code. But how to make them continuously change?
There are two choices. Each wave has a height, essentially a strength or loudness. These waves are electrically converted from sound to electricity by a microphone. By rapidly making the electrical signals it receives louder and softer—i.e., their peaks taller or shorter—a transmitter coupled with the appropriate receiver can encode and detect these rapid fluctuations and translate them into the original sounds by using a rapidly vibrating magnetically driven speaker. This is amplitude modulation, or AM.
The other method is to rapidly change the frequency of the waves, meaning subtle variations in their wavelengths, by causing a sudden spurt of more or fewer waves. This frequency modulation, abbreviated as FM, allows for a greater clarity of transmission and reduces static and interference from electrical equipment. Early radio was exclusively AM; the first experimental FM broadcasts didn’t begin until 1937, the process having been patented four years earlier by inventor Edwin H. Armstrong.
In June of 1912 Marconi opened the world’s first radio factory. The first news program was broadcast on August 31, 1920, by station 8MK in Detroit, Michigan, which survives today as an all-news station affiliated with the CBS network. As for the first public entertainment broadcast in the United States, that, too, came in 1920, with a series of Thursday night concerts.
If only Hertz, Maxwell, Faraday, and the other early pioneers of wireless telegraphy and radio could see the world now. They would stand in awe of what would probably seem to them like magic. Consider the GPS system found in virtually every car and cell phone. How much do you know about the work it’s doing constantly? Atomic clock signals broadcast by two dozen satellites send out time signals using short radio waves—nowadays categorized as microwaves. Your GPS receiver needs to receive only four of those signals to determine your exact location on the planet. It knows the right time to a billionth of a second and immediately discovers that all those satellite signals it’s receiving are delivering the wrong time. Wrong because those Hertzian waves, traveling at light speed, require a little bit of time to reach you—about one-seventeenth of a second—from their orbital height of eleven thousand miles.
The delay is caused by the time it takes light to travel. Your receiver, perceiving a certain precise delay from satellite A, a different delay from satellite B, and so on, can calculate how far away each orbiter must be to produce that out-of-date time signal. Then it calculates the one spot on earth where you must be located in order for you to be positioned at that exact distance from each satellite. Voilà: your location, to an accuracy of a few feet. Because your GPS also knows where you are each time it performs a triangulation, it knows how fast you must be moving and in what direction. Equipped with onboard maps, it can then determine how long it will take you to reach Cleveland or any other place you’re going.
All using radio waves.
This wouldn’t work if light were so
fast that it took no time at all to travel. And it wouldn’t be practical if light’s speed were too slow—matching that of sound, say. So if some of our major technologies revolve around the speed of radio waves and other forms of invisible light, maybe we’d better take a closer look at that speed.
CHAPTER 11
The Speed That Destroyed Space and Time
Light—visible and invisible—has a weirdness that extends far beyond its “not really there if no one is looking” quality. Many of its oddest effects involve its speed, probably the most famous velocity in all of science. You see, at high speeds or in places with a strong gravitational pull, all kinds of funny things happen, and since they affect light, they affect a lot of other things as well. At superhigh speeds, time slows down—not good if you have a boring job—and distances shrink. This phenomenon, known as time dilation, is amply explored in science fiction, as it was in the 2014 blockbuster movie Interstellar, in which astronauts on the surface of an alien planet experience the passage of only a few hours while their colleague in orbit grows several decades older. But the contraction of the distances between objects is much less widely appreciated.
The fact that neither time nor space has definable boundaries was first expressed in a famous equation devised in the final years of the nineteenth century by Hendrik Lorentz. A few years later, when Einstein explained them, he used the same math, which is why the specifics of the mutation of time and space is still called the Lorentz transformation. The equation shows some of the astounding possibilities: if you could travel at 99 percent of the speed of light, the universe would suddenly become seven times smaller than it is now. A star around fourteen light-years away (such as Altair, in the Summer Triangle) would magically float to a distance just two light-years away—reachable before you’d aged very much. At that speed, a living room shrinks to barely three feet wide.
As you zoom faster, the effect becomes truly dramatic. Traveling at 99.9999999 percent of the speed of light would produce a dilation factor of 22,361. Your rocket’s clock would tick off just one year while more than 223 centuries simultaneously elapse back on earth. In addition, all distances would shrink by this same percentage. You could reach the core of our galaxy in a single year—as compared to four hundred million years using today’s fastest rockets. With that much territory at your disposal, your social life could expand enormously. You could hold your next party near the black hole at the galaxy’s center and toss popcorn in just for laughs.
But you’d be laughing alone. Back on earth, clocks would continue to tick and tock at their old customary rates. When you returned from your round-trip, the party would really be over. While you and your crew experienced two years and would look only that much older, fifty thousand years would have elapsed back on earth. The map of the world would have changed utterly; customs and language would be unrecognizable to you. There would even be evolutionary alterations in some life forms. You’d be seriously old-fashioned, and it would go far beyond whether bell-bottoms and wide ties had come in or gone out. You’d be lucky if they didn’t throw you in a zoo.
When pondering the space- and time-altering effects of approaching the speed of light, the easiest way to keep things straight is to remember that, to you, time always passes normally and never seems to change. If you’re lucky enough to live for eighty-five years, you’ll experience that passage of time in the normal way, regardless of your velocity. It’s just that others watching you through telescopes will age differently and observe you aging slowly, even though you experience no such alteration. Bottom line: it’s always “the other guy” whose time passes weirdly. It’s never you.
But you do experience shrinking space. When you approach the speed of light, the distance ahead to your destination does indeed contract, so you get there much sooner than you would if space weren’t shrinking. In addition, at close to the speed of light, everything in the universe would seem to lie directly ahead, no matter which way you point your rocket.
Okay, this requires some explanation: it’s the principle of aberration. When walking briskly through a rain shower, we must tilt our umbrella forward a bit to keep from getting wet. And when we drive through a snowstorm, the flakes seem to come from straight ahead while the rear window hardly gets hit at all. These are examples of aberration, which means a shift in the position of an object. Light, too, gets changed in this same way. Earth’s motion around the sun at a mere 18.5 miles per second shifts the night’s stars so that they’re slightly displaced from where they’d appear to be if we weren’t moving. If we traveled faster, this effect would increase until, at just below light speed, everything in the universe would seem to be located dead ahead. So looking out our rocket’s windshield, we’d see a single dazzling “star,” which would actually be everything in the universe clumped into one brilliant ball. Out the rear window we would see inky blackness, because space would be so warped that nothing at all would lie in that direction.
In short, a star’s position is changed because of our own motion through space!
Light possesses a magician’s chest full of illusions and tricks. Its speed, that famous constant of 186,282.4 miles per second (or 299,792,458 meters per second), refers to its velocity through empty space. But light moves more slowly through denser media such as glass (120,000 mps) and water (140,000 mps). So the light rays that convey all the colors and shapes outside your window through the pane and to your eyes abruptly slow down when they strike the glass. Then they instantly speed up again once they’re finished penetrating it. Light travels slowest of all through a diamond, because each color contained in the light moves at its own distinct velocity through the gemstone. This difference in speed is why a diamond flashes, giving it its coveted brilliance.
Despite many attempts, nobody could figure out the speed of light until a few centuries ago. It was just too fast to measure. Not that many determined “natural philosophers” (as scientists were then called) didn’t make heroic efforts to do so. In 1629, Dutch scientist Isaac Beeckman positioned large mirrors at various distances from gunpowder, which he’d explode, creating a flash. His helpers were instructed to observe the flash directly as well as watch its reflection in a distant mirror, light from which would thus need to travel a greater distance to their eyes. Would they detect any lag or delay between the two flashes—the direct event and its reflection in a faraway mirror? Answer: no.
Three years later, Galileo gave it a try. The cranky bearded genius stood on a hilltop and positioned an assistant with a shuttered lantern on another hilltop, one mile away from him. Galileo opened his lantern, and the assistant was supposed to hit the quick-release shutter to his own lantern as soon as he saw Galileo’s light. Galileo would then measure how long it took before he saw the “responding” light from the other hilltop. By measuring the elapsed time and knowing the distance between the lanterns, he would determine the speed of the light.
In reality, light’s round-trip travel time between two hilltops a mile apart would be 1/100,000 of a second. Good luck, Galileo. He concluded, “If not instantaneous, [light] is extraordinarily rapid.” He ended up declaring that light travels at least ten times faster than sound. (Sound travels around one-fifth of a mile in a second, or around a million times more slowly than light.)
The Danish astronomer Ole Rømer finally obtained the first reasonable light-speed measurement without having to trudge up any hills. In 1675, when he was thirty-one years old, he explained why Jupiter’s four bright giant moons all bewilderingly sped up in their orbits for half of each year, whenever Earth was heading in Jupiter’s direction. It’s logical, he explained: the images of Jupiter’s moons’ positions reach us sooner under those conditions because each second their light doesn’t have quite as far to travel as it did before. The end result is to make them seem to zoom around that planet in high-speed Charlie Chaplin fashion. Not knowing the precise distance to Jupiter was his only weak link; nonetheless he correctly nailed light speed to within 25 percent accuracy.
These days, to measure light, we use an apparatus first devised in the middle of the nineteenth century by the famed French scientist Léon Foucault. It works by shining a light beam at a rapidly rotating mirror, which reflects the beam to a distant fixed mirror, which then reflects it back. While the photons are making their little round-trip journey, the whirling mirror’s face slightly changes its angle so that the final bounce gets reflected to a slightly different position on a graduated scale in an optical detecting device. Knowing the speed of the whirling mirror (Foucault’s spun five hundred times a second) and the distances between all the mirrors, and taking into account the amount of light-path deflection read from the scale, one can nail light speed to an accuracy of one part in a million. I’ve done it myself; these days it is almost routine among scientists.
Light is indeed superfast, but we can now comprehend the speed; it’s not infinite. If only the ancient Greeks could be here to share with us this small miracle—that we can actually measure the fastest thing in the universe.
We use light’s steady speed in our technology and in our scientific experiments—and from it we learn new things. For example, several college research programs bounce laser flashes off the three corner cube reflectors left on the moon by the Apollo astronauts. The delay in receiving the reflection is always around two and a half seconds; precise measurements allow us to gauge the moon’s changing distance from Earth to an accuracy of within one inch. It’s revealed that the moon is constantly moving farther away from us at the rate of one and a half inches a year.