The Physics of Superheroes: Spectacular Second Edition

by Kakalios, James

  20

  ELECTRO AND MAGNETO DO THE WAVE—ELECTROMAGNETISM AND LIGHT

  IN THE MID-18 00S, the expanding American frontier may not have seen many costumed crime-fighters, but there was no shortage of heroes willing to fight for truth, justice, and the Western Way. A good thing, too, as a century later, Western comics would tap into an upsurge in the popularity of cowboys in the 1950s and thereby help keep comic-book publishers solvent during the superhero crunch precipitated by the campaign launched by Dr. Wertham’s Seduction of the Innocent. All-American Comics, featuring the adventures of Green Lantern and the Justice Society of America, became All-American Western—starring the “fighting plainsman” Johnny Thunder (schoolteacher by day, gunfighter by night)—and All-Star Comics became All-Star Western and detailed the adventures of the Trigger Twins. In the DC universe, the scarred (physically and psychologically) rebel loner Jonah Hex traveled across the western United States, righting wrongs and saving widows. Similarly, Bat Lash and the Vigilante dispatched justice . . . well, vigilante-style. Over in the Marvel universe, Western comics were strictly kid stuff, with the Two-Gun Kid, Kid Colt, Ringo Kid, and the Rawhide Kid working essentially the same beat, moving from town to town every issue (though rarely bumping into one another), facing down rustlers and stagecoach robbers. Back in the real mid-nineteenth-century world, when cowboy lawmen were cleaning up Dodge, physicists were seeking to tame the wild frontiers of electricity and magnetism, in the process laying the foundation for our modern wireless lifestyle.

  It was the Scottish physicist James Clerk Maxwell who, in 1862, made the monumental theoretical leap connecting electricity and magnetism and ushered in a new era of scientific advancement. The set of equations elucidated by Coulomb, Gauss, Ampère, and Faraday is nowadays known by the general title of “Maxwell’s equations,” in recognition of his utilizing them to provide a fundamental understanding of electromagnetic radiation. None of these scientists have ever starred in their own comic books, but without these heroes, we’d still be reading by candlelight.

  In order to understand how an electric lightbulb works, think back to the water analogy we invoked earlier to explain electric currents: The water pressure of the faucet was analogous to an electrical voltage, while the amount of water per unit time flowing through a hose represented the electrical current. To indicate that the hose was not perfect, and that a finite pressure had to be continuously applied to maintain a steady flow through the hose, we suggested that the hose had both partially blocked regions as well as small pinholes along its length, through which water could escape and avoid participating in the main current flow. For a given hose’s resistance, the greater the water pressure, the larger the water current. Alternatively, for a fixed water pressure, the larger the resistance, the smaller the current. These commonsense principles can be combined into a simple equationVOLTAGE = (CURRENT) × (RESISTANCE)

  known as Ohm’s law, after Georg Ohm, another pioneering scientist in the early days of electromagnetism, for whom the basic unit of resistance (an Ohm) is named. The longer and skinnier the hose, and the more clogs and holes along its length, the larger its resistance to current flow. A large water pressure at one end of a long narrow, leaky hose will correspond to a bare trickle at the other end, several miles away from the faucet. This is why your jumper cables are relatively short and thick, so that the current supplied from one car battery is not degraded by the time it reaches the second battery.

  The pinholes in the hose represent energy loss, and account, in our water analogy, for why a uniform water pressure (force) leads to a constant water current, and not an accelerating flow as Newton’s second law (F = m × a) would indicate. Copper wires obviously do not have holes through which the electrons leak out, but they do have resistance. At one end of the wire, the electrons feel a large force due to the accelerating voltage. Hence, they have a large potential energy. As they flow down the wire, their potential energy is converted to kinetic energy. The greater their kinetic energy, the faster the electrons will move down the wire, and the larger the current. Imperfections or impurities in the wire act as speed bumps, and the fast moving electrons collide with these defects, transferring some energy to them and causing the atoms to vibrate (which is why the wires become hot). The balance between the kinetic energy gained by the electrons from an applied voltage and the energy transferred to the imperfections determines the current.

  These imperfections are impurities or atoms that are out of crystalline alignment with the rest of the lattice. As such, they have their own cloud of electrons surrounding them, just as the other atoms in the wire do. When these imperfections shake back and forth after collisions with the electrical current, their electric charges oscillate.

  Consider a variation on the swinging pendulum in Chapter 10, in which the mass attached to a thin string now also carries an electric charge. As the charged mass swings back and forth, it is an electrical current, but one for which the speed of the charge’s motion continuously changes (high velocity at the bottom of the arc, zero velocity at the highest points of the swing). As such, it generates a magnetic field that is also changing in magnitude. However, a changing magnetic field induces an electric field. The oscillating charge will therefore continuously generate a varying electric field in phase with a changing magnetic field, radiating out into space. The faster the charged mass swings back and forth, the higher the frequency of the electric and magnetic oscillations created. Since the electric and magnetic waves have energy, the oscillating, charged pendulum will slow down, even if there is no air resistance. There’s a special name for the oscillating electric and magnetic fields created by the simple harmonic motion of the charged pendulum: It’s called light.

  WHY THE X-RAY SPECS ADVERTISED IN COMIC BOOKS ARE A TOTAL RIP-OFF

  In a wire carrying an electrical current, colliding with impurity atoms, the oscillating electric charges in these atoms give off alternating electric and magnetic fields. The faster the electrons connected to the imperfections in the wire oscillate, the higher the frequency of the electromagnetic waves that are generated. Just by being at room temperature, all of the atoms (and their electrons) in the wire are vibrating at a rate of approximately a trillion cycles per second. Therefore any object at room temperature emits electromagnetic waves with a frequency of a trillion cycles per second. Electromagnetic waves with this vibration frequency are called infrared radiation. The greater the temperature, the faster the atoms in the object shake, and the higher the frequency of the emitted radiation.

  Depending on how fast the charges in the atom are shaking—that is, how many times a second they move back and forth—the emitted electromagnetic waves can have a wavelength (a measure of the distance peak to peak of the wave) of several feet all the way down to the diameter of an atomic nucleus. In the first case, we call these long-wavelength electromagnetic waves “radio waves” (with a frequency of roughly a million cycles per second) and in the second case, these ultrashort waves are termed “gamma rays” (with a frequency of more than a million trillion cycles per second). Gamma rays have more energy and can therefore do more damage to a person than radio waves—as reflected in the fact that no one has ever gained superpowers by standing too close to an FM broadcast antenna. But they are both the same phenomenon. In order for the atoms in a wire, such as the thin filament inside a lightbulb, to emit electromagnetic waves that our eyes are able to detect—which we call visible light—the atoms must be shaking back and forth roughly a thousand trillion times per second.

  We are finally in a position to understand why the sun shines. As mentioned in Chapter 2, the intense gravitational pressure at the center of the sun means that protons (hydrogen nuclei) collide frequently, so that some fuse together to form helium nuclei. The mass of a helium nucleus is slightly less than that of the two protons and two neutrons separately, and the mass deficit corresponds to a great energy output, through Einstein’s expression E = mc2. This outgoing energy balances the inward gravitatio
nal attraction, and the sun remains relatively stable as it burns through its fuel (and a lot of fuel it burns—600 million tons of hydrogen nuclei every second!). Part of the energy resulting from this fusion reaction is in the form of kinetic energy, and the rapidly moving, accelerating, charged helium nuclei emit electromagnetic radiation. Acceleration is the rate of change in velocity, and so every time the helium nucleus speeds up, slows down, or changes direction as it collides with other nuclei in the dense stellar core, it emits light. The light we see from the sun is very old, as it slowly makes its way from the center of the sun to the surface. It is difficult to see anything on a foggy night because the dense water-saturated atmosphere scatters the light in all directions. It’s much denser within our sun, and the light generated from a nuclear-fusion reaction takes an average of 40,000 years to diffuse from the core to the surface of the sun.

  Our eyes can see visible light because most of the electromagnetic waves from the sun that make it through the atmosphere are in this portion of the electromagnetic spectrum. When creatures without eyes evolved into creatures with eyes on this planet, the eyes they developed were sensitive to the type of electromagnetic waves that were most prevalent. Much fewer X-rays emitted by the sun reach us compared with light in the “visible” portion of the spectrum. Consequently, if our eyes were such that we could see only X-rays, we would live in a world of near-total darkness. Those creatures that do live in total darkness, such as sea life at the ocean’s deep bottom where sunlight does not penetrate, do not waste genetic resources on superfluous eyesight or skin pigmentation, but rather rely on other senses to navigate.

  Back in the Silver Age of comic books, unscrupulous salesmen, preying on the prurient interests of comic-book readers, sold “X-ray glasses” that promised the wearer would be able to see through solid objects such as clothing. Even if these X-ray specs employed a principle similar to “night vision” goggles, which translates infrared radiation into the visible (more on this in Section 3), there are not enough X-rays outside of a dentist’s office to make this a useful product. And just try getting your money back from these companies!

  Animals that are primarily nocturnal devote more of their optical receptors to high-sensitivity rods, sacrificing color vision by having fewer cones, in order to detect the few electromagnetic waves present. But any animal or person that evolved “X-ray vision” would spend most of its time bumping into things, and would be at a distinct evolutionary disadvantage. The more electrons an atom has, the more strongly it scatters X-rays. This is why X-rays can penetrate through the soft tissue of a living body (which is mostly water) but are reflected from the much denser bone. Presumably Superman is able to emit X-rays from his eyes, which then penetrate through low-X-ray-absorbing matter before being reflected and then detected by the Man of Steel. Those not from Krypton can see only when light from an external source is reflected into their eyes from an object. It costs the human body energy and raw materials to develop optical-nerve cells sensitive to low-wavelength light; consequently, there is little point in developing an ability to detect the odd, occasional X-ray.

  I CAN TELL THAT YOU’RE THINKING YOU WISH YOU HAD A TINFOIL HELMET

  The leader of the mutant team of superheroes known as the X-Men is the wheelchair-bound telepath Charles Xavier, also known as Professor X. While his shattered spine may have left him unable to walk, he was a formidable general for this team of “good” mutants thanks to his ability to read and project his thoughts into other people’s minds. The physical basis underlying Prof. X’s telepathy (and that of his protégée Jean Grey, and Saturn Girl of the Legion of Super-Heroes, as well as Aquaman’s fish telepathy, for that matter) is that time-varying electrical currents can create electromagnetic waves detectable to someone who is supersensitive.

  All cells in our body have a function. Muscle cells exist to generate a force, whether it is for the flexing of the biceps or the pumping of the heart. Liver cells filter impurities from the bloodstream, while stomach and intestinal cells put them there in the first place. The role of nerve cells or neurons is to process information. One way they accomplish this is by transmitting and altering electrical currents. The charged objects that move from neuron to neuron are not electrons, but calcium, sodium, or potassium atoms that are either missing one or more of their electrons or have acquired extra electrons (such charged atoms are termed “ions”). An accumulation of ions in one region in the brain creates an electric field that in turn coerces other ions in other neurons to move. The moving ions constitute a current that generates a magnetic field. Experiments by neuroscientists using sensitive electrodes placed within the brain can detect the electric fields generated by the motion of these ions, which typically vary randomly in time. Depending on where in the brain the electrode is located and what task the brain is performing, the electric fields recorded will assume a coherent wave form, oscillating through several periodic cycles before abruptly returning to the random background. Neuroscientists are beginning the difficult task of identifying the voltage variations and determining their significance (if any) with behavioral tasks. From such simple building blocks, the human mind, with all its vast complexity, is constructed.

  While scientists are a long, long way from understanding how or whether the ionic currents in the brain lead to consciousness, there is one aspect of the neuronal currents that we may rely upon: that moving electric charges generate magnetic fields. In turn, because the ionic currents in the brain are continually changing direction and magnitude, the corresponding magnetic fields vary in time and create electric fields as well. The net effect is that very-low-frequency electromagnetic waves radiate out from the brain whenever electrical activity occurs. The wavelengths, amplitudes, and phases of these electromagnetic waves are determined by the time-dependent ionic currents from which they originate. The amplitude of these waves is extremely weak, such that their power is more than a billion times lower than the background radio waves that surround you at this very moment (ordinarily, the fact that we live within a sea of radio-broadcast signals is ignored, until one turns on a radio and can’t tune in a particular station clearly). Yet the electromagnetic waves created by brain currents do exist, though their intensity is too weak to be observed unless the sensor is directly on the person’s head. For certain powerful mutants such as Prof. X, or residents of the moon Titan in the thirtieth century (Saturn Girl), their miracle exception involves brains sensitive enough to detect the electromagnetic waves generated by others’ thoughts. Of course, if you are wearing a metal helmet (a precaution taken by Xavier’s evil step-brother, the Juggernaut; Magneto; and other farsighted X-Men foes) then your head is shielded so that the outgoing (and any incoming) electromagnetic waves are grounded out.

  Aquaman’s ability to talk to fish presumably functions in a similar manner. Given that sea water is roughly a million times a better electrical conductor than pure, deionized water, and a hundred trillion times better a conductor than air, Aquaman starts with a considerable advantage in being able to detect and send weak electromagnetic signals. It also helps that fish have a specific organ that generates weak electric fields and separate receptors to detect these fields. Fish use these organs as a form of radar, helping them navigate in brackish waters or at night. Some fish, such as sharks, skates, sturgeons and sawfish (the first type of fish he communicated with in More Fun Comics # 77) have extremely sensitive electroreceptors that can detect a voltage as small as a millionth of a Volt a centimeter away—such sensitivity is difficult to achieve in the laboratory! Consequently, it would be surprising if the Aquatic Ace were not able to talk to fish—apparently he possesses the necessary language skills to make his wishes known to such simple life forms thanks to his Atlantean heritage.

  A stone tossed into a pond creates a series of ripples that grow weaker the farther one is from the source. The water molecules have a great deal of kinetic energy imparted from the falling stone. But as the ripple becomes larger and larger, the amount of energy
in the water molecules is spread out along the growing circumference, so that for a stone dropped in the middle of the Pacific Ocean there is no noticeable disturbance at the California coast. In the same manner there is a decrease in the intensity of electromagnetic waves the farther one moves from their source. The fact that the intensity of electromagnetic waves decreases with distance from the source of the waves explains why, when Professor X needs to locate a particularly distant mutant, he uses an electronic amplifier of his mental powers, called Cerebro. First introduced in X-Men # 7 as an automated mutant brain-wave detector, it was adapted in later issues to increase the sensitivity of Prof. X’s telepathic powers. The recognition that in order to detect a distant electromagnetic signal, one would have to use an external amplifier, is consistent with the physical mechanism underlying Prof. X’s mutant power. This is also why radio and television broadcast stations use megaWatts of power to transmit their signals. Recall that a Watt is a unit of power, defined as energy (in Joules or kg- m2/sec2) per second, and a megaWatt is a million Watts. The more power a radio station can broadcast, the greater the intensity of the electromagnetic waves reaching a given remote antenna, and the stronger the signal received by the radio. Commercial radio stations generate their signals by oscillating charges up and down a big antenna. Your television set or radio does not employ Cerebro technology to amplify the distant signal, but it does make use of transistors for this function, which we will discuss in detail in Chapter 24.