The Canon (20 page)

The transmission of electric current requires a circuit, a pathway of atoms amenable to bartering charged particles, growing excited in the process, and propelling that wave of kinetic energy forward. Yet electromagnetic energy, that is, electromagnetic radiation, needs nothing to propagate it from here to there. Waves of electromagnetic energy can travel just fine through a vacuum, which is lucky for us, or we'd die of cold and hunger and an unslakable longing for the sun. Because the term "electromagnetism" encompasses so many different concepts—the attraction between electrons and protons in an atom and between socks and sheets in a dryer, the flow of charged particles through a wire and the bilious glow of a fluorescent light bulb—it can be easy to overlook or misconstrue the specific beauty of electromagnetic radiation and the incomparable lightness of light.

Nearly all the energy on which we earthlings rely begins with the waves of electromagnetic radiation that billow forth so extravagantly and implausibly from our sun. We may burn coal to make steam to turn turbines to spin coiled copper to make an electric current to heat and light our house on a winter's night, and we may chemically and pyrotechnically "refine" crude oil extracted from thick layers of mudstone, limestone, and calcium sulfate beneath the Saudi Arabian desert into the petroleum that runs our vehicles, but all those "fossil fuels," those stashes of archaic vegetable matter compacted into dense energy candy through 300 million years underground, were fueled first by sunlight. Plants have the molecular tools to capture solar radiation and put it to use. Plants then become food for others—fast food for the cherry pickers of today, or slow food as the fossil fuels of the future. No matter: the real hero here, the author of every story and the wearer of every toque, is the sun. "When you eat a green, leafy vegetable, you are eating photons of solar energy," said Daniel Nocera of MIT. "You are biting the light of the sun."

We tend to think of sunlight as the light that we see, that the cells of
our retina are able to capture and transmit as nerve impulses to be interpreted by the brain. We think of sunlight, in other words, as what we call "visible" light, the small slice of the electromagnetic spectrum that our human eyes can see. Yet most of the sun's light is metaphorically dark, is outside the tiny percent of the electromagnetic spectrum that our relatively impoverished vision can detect. If the sun were a Baskin-Robbins shop with 100 billion flavors on the menu, we would be capable of tasting only 5 of them. We're aware of some of the sun's invisible powers—the thermal radiation that feels warm on the skin, the ultraviolet radiation that makes wrinkles begin. But there are many other species of the electromagnetic spectrum, many ways you can wave and stay light on your feet. Here's a little riddle that Bob Mathieu of the University of Wisconsin in Madison would like everybody to be able to answer. "What do all these things have in common: radio waves, microwaves, infrared, optical, ultraviolet, X-rays, and gamma rays?" he asked rhetorically. "They are all light."

Fine. They are all light. They are all electromagnetic radiation. They are all—what? Electromagnetic radiation is really a couple of big moving fields, one electric, one magnetic, traveling together at right angles to each other. Hard to envision, I grant you, but think of this: An electron is surrounded by an electric field, the charismatic attitude, or force of personality, that other charged particles respond to. If you move a stream of electrons back and forth quickly along a metal conductor, the herking and jerking of their electric fields will generate a magnetic field, which wraps around that conductor the way your fingers wrap around a bicycle handle. The newborn magnetic field in turn provokes the formation of yet another electric field, which then takes up the dare and creates a new magnetic field. Iteration and reiteration, Pete and Repeat, the electric and magnetic fields continue spooling out novel counterpart fields. And as each neonatal field arises, it can amplify, diminish, or otherwise modify the existing fields, depending on whether the fields' peaks and troughs synchronize or interfere with each other. This oscillating blossoming of fields begins rippling outward as electromagnetic radiation—as light. The electrons may be stuck on their trolley line, but the electromagnetic field they fomented can break free and soar through the air or through no air at all, traveling at 300,000 kilometers per second, the universal speed limit at which light has license to fly.

All types of electromagnetic radiation can travel at the speed of light, but they do so with their distinctive style. Depending on how their mutually interacting and propagating fields manipulate one another, light waves may journey in long, gentle swells or compressed, nervous spikes,
or any dimension between. You may get a pure signal of like-minded waves or a sampler of shorties, mediums, and XXLs. It is similar to what happens when you drag your hand back and forth through bath water. If you whip up the water haphazardly, peaks and troughs and froths of varying sizes will emerge from the stir. If you get into a cadence of swishing, however, you can instigate a smooth, sinuous, motivated wave, which would surely buoy a rubber duckie outward through all space, time, and divinity if not for the walls of the tub.

Our versatile sun bakes up a banquet of electromagnetic fields and radiates light across the spectrum. But because it is a medium-sized, middle-aged star that, in the stellar scheme of things, is only under moderately high pressure at its core—the source of its electromagnetic glow—a handy proportion of its light is of spritely but not histrionic energy, leaping through space in graceful, compact wavelengths. Those wavelengths happen to lie in or near the visible zone of the electromagnetic spectrum, although "happen to" has nothing to do with it. Our eyes evolved to respond as best they could to ambient light, and the sun is very good at propagating light waves that are between 15 and 32 millionths of an inch long. This is the slice of light that we immodest
Homo taxonomists
have designated as visible light, or optical light, or daylight. Yet the terms are terribly blinkered. Other animals can see light lying well outside the so-called visible range—in the ultraviolet, in the infrared, in radar. Bees, for example, see perfectly well in the ultraviolet range, and many flowers beckon their pollinators with ultraviolet stripes, while the pits of a pit viper detect infrared light, the signature thermal radiation that emanates from meal and menace alike.

Different wavelengths of light are adept at different feats. Radio waves, being very long, can travel without being absorbed or scattered by air molecules, and the longest ones bend readily around the curve of the Earth. They are therefore excellent at transmitting broadcast signals from far-flung radio and television stations to the appropriate receiving device in your home or automobile or, as some people swear, the fillings in one's teeth.

Next down on the electromagnetic spectrum is the ill-named light brigade, microwave radiation. Microwaves are not micro at all, but reasonably wide-bodied, extending from about a centimeter up to a meter in length. Like radio waves, they're long enough to convey signals through the air unfazed. Unlike radio waves, they can be focused into a highly directional beam and hence transmit the signals from one horned antenna to another with a relative degree of security and privacy. Radar is a form of microwave radiation, a directional pulsing of
microwaves that reflect off solid objects and back to a receiver, revealing the location of pinged objects with extraordinary precision. A top-of-the-line radar can pinpoint the whereabouts of a housefly two kilometers away, although clearly this is a radar with far too much time on its hands.

Over on the other end of the spectrum, we have X-rays, which are extremely short, about a ten millionth of a millimeter across, or roughly the width of an atom. X-rays are energetic enough to pass directly through most parts of the body but are absorbed by high-density tissues like bone. Yet despite their long-standing utility to medicine, dentistry, biology, and astronomy, X-rays have yet to shed their campy secret-agent of an alias, bestowed on them in 1892 by their discoverer, Wilhelm Roentgen, because he had no idea what they were. Even after the electromagnetic nature of X-rays was elucidated, the quizzical consonant stuck, and by the looks of it will forever mark their spot.

Moving past X-rays, we come to gamma rays, which are pretty much as cinched a wavelength as we can measure. Gamma rays are shorter than a proton's bow tie, but they shoulder massive backpacks of energy. The sun's gamma rays do not make it through our stacked atmosphere without getting lost in the bowels of air molecules en route. Nevertheless, the rays are potentially hazardous to human health and its services. People who fly frequently on long intercontinental flights that cruise through the diaphanous stratosphere six or eight miles above Earth may be exposed cumulatively to undesirable quantities of solar gamma radiation. And should a star located anywhere within about 25,000 light-years from the Earth explode into a supernova, the burst of gamma rays thus unleashed could well knock out entire telecommunication systems. Cell phones, blogs, e-mail, e-dating, e-gads—life as we know it e-rased in a flash.

On the flossy face of it, nature doesn't act like much of a miser. At the end of each spring, forest floors are littered with hundreds of times more fallen blossoms than could ever have borne fruit, and armies of sprouting acorns that will die long before they crown, and the bones of fledgling songbirds that proved surplus and were expelled from the nest. As the brain of a human fetus grows, one hundred neurons must die for every brain cell that settles in and synaptically connects to its neighbors; and the prenate's fingers and toes likewise are whittled down from primordial flippers that fan out from the ends of its limbs.

In its daily sixteen hours of grazing, an elephant eats the equivalent of its trunk's weight in food: three hundred pounds of grass, leaves,
roots, bark, branches, bamboo, berries, corn, dates, coconuts, plums, sugar cane, and, as I discovered in my girlhood, Ring-Dings. The elephant's intestines extract only a small portion of the nutrients in that extraordinary intake, though, and the rest is discarded in a similarly astonishing output of about two hundred pounds of dung per day.

Yet beneath nature's extravagant breast lies a thin-lipped bursar, tallying every bean and brain cell, pricing every sheaf of grass. Nature is a tenacious recycler, every dung heap and fallen redwood tree a bustling community of saprophytes wresting life from the dead and discarded, as though intuitively aware that there is nothing new under the sun. Throughout the physical world, from the cosmic to the subatomic, the same refrain resounds. Conservation: it's not just a good idea, it's the law. Isaac Newton discovered some of the laws of conservation. By the law of the conservation of momentum, for example, if a 5,000-pound, all-terrain SUV traveling at 30 miles per hour were to slam headlong into an angry 12,000-pound elephant ring-a-dinging toward it at 25 miles per hour, the relatively more momentous product of the elephant's mass multiplied by its pace would be only partly offset by the opposing but smaller momentum of the moving vehicle, and some of that elephant ire would be transferred to the vehicle, tossing it backward and into the nearest baobab tree.

The law of the conservation of charge means that for every positive charge generated over here, there has to be a net negative charge somewhere else: if, through combing your hair, you turned a few strands into mutually repulsing objects of positivity, you must have infused your comb with extra electrons. You can't snuff out or neutralize a particle's innate charge, and, as far as scientists can tell, the universe is electrically balanced: for every electron there is a proton (turn, turn, turn). You cannot drum up a negatively charged atom or group of atoms—a negative ion—without simultaneously yielding a positive ion.

Perhaps the most profound of all the preservation statutes—and one of two laws of conservation that scientists repeatedly told me they wished the public understood—is the law of the conservation of energy, also known as the first law of thermodynamics. I've long loved the word "thermodynamics," for both its sound and sense of heat in motion. The science of thermodynamics is the study of the relationship between kinetic and potential energy, and heat. The major premise under-girding the discipline is this: in a closed system, the total amount of energy, including heat, is always conserved. Energy cannot be created, replicated, or conscripted from other dimensions. Energy cannot be destroyed, redacted, or forced into early retirement. Energy can only
change hands or be converted from one form to another. The qualifying phrase here is "in a closed system." Many systems we encounter in our daily lives are not closed. If you're boiling water on the stove, you can continue adding more energy to the system—that is, the saucepan—simply by keeping the burner on. The kinetic energy released by the protracted combustion of natural gas will be transferred steadily to the water molecules, causing them to bobble about faster and faster until they undergo a phase shift and turn to gas. Even after all the water has boiled away, the energy from the burning natural gas can continue working the system, oxidizing the metal alloys of the saucepan and rupturing the bonds among them, and melting the tough resin polymers of the handle, until finally you, the negligent cook, will need to open another system—the windows and doors of your home, to clear the kitchen of the stench of your favorite saucepan gone to pot.

Other familiar systems, though, are effectively closed—for example, a child on a playground slide. The child climbs to the top of the slide, gathering potential energy in the ascent. The child then sits at the top of the slide, takes a breath, makes sure the parent or guardian is watching with the appropriate mix of excitement and admiration, and lets go, cashing in the stored gravitational energy for the thrill of kinetic energy, along with the inevitable sideline seat warmer of heat. If you added up the kinetic energy of the descent and the energy transferred by heat to the slide, the child's bottom, and the air molecules she rushed past, the sum would equal the gravitational energy with which the transaction began.