The Physics of Superheroes: Spectacular Second Edition (14 page)

Finally, what about the third possibility—shrinking a person by making him denser by pushing the atoms closer together? Unfortunately, this is not a successful strategy for miniaturization either, for the same reasons that the planet Krypton could not simply be fifteen times denser than Earth. Atoms in most solids are already tightly packed, with each atom essentially in direct physical contact with its neighbors. Moreover, thanks to the repulsion of negatively charged electron probability clouds around each atom, they are fairly rigid objects and resist being squeezed together. When a box is filled to the top with a child’s collection of marbles, nearly all of the container’s available space is taken up by the marbles. With few exceptions, every marble is in physical contact with several of its neighbors. Certainly there are open gaps between the marbles, but these spaces are not big enough for us to add more than possibly a few percent more marbles. If the marbles are hard spheres and not compressible, then squeezing on the walls of the container will not lead to a significant reduction in its volume. Reducing the size of the container by a factor of ten would require pressures that would significantly deform or crush the marbles. Trying to shrink a person by applying similar pressures would result in comic-book stories that would be both brief and messy and almost certainly would not garner approval by the Comics Code Authority.

Well, if miniaturization is so difficult, how does biochemist Dr. Henry Pym, also known as the Ant-Man, accomplish it? In
Tales to Astonish # 27
, Pym had devoted years to discovering a potion that would shrink any object, until treated with an antidote growth serum. Later, he would convert his shrinking potion into an easy-to-swallow pill form. When it eventually became necessary to explain how he was able to shrink other objects, such as his costume, helmet, and weapons that he carried, it was revealed that he had developed a small generator of “Pym particles” that were able to increase or decrease an object’s size. No explanation has ever been put forth for how these potions or Pym particles actually work, and their physical basis must fall under the “miracle exemption” we frequently invoke when considering the source of a hero’s superpowers.

6

SO HE TALKS TO FISHES. WANT TO MAKE SOMETHING OF IT?—
FLUID MECHANICS

WHILE SUPERMAN, Spider-Man, Batman, and the Hulk are considered A-list superheroes, there are those who fight the never-ending battle, yet seem to garner little respect. Despite facing world-shaking threats and being present at the creation of a variety of superhero teams, these heroes are, unfairly, I would say, relegated to the ranks of second-stringers or worse. I am here referring to such champions as Ant Man (a founding member of the Avengers), Bouncing Boy and Matter- Eater Lad (both early members of the Legion of Super-Heroes), as well as an original participant of the Justice League of America: the King of the Seven Seas, the Aquatic Ace, Aquaman.

In Chapter 8 we will see how Henry Pym, despite being only a quarter of an inch tall when fighting for justice as the astonishing Ant Man, is still able to punch his way out of a paper bag (a minimum prerequisite in the superhero game). Bouncing Boy will make an (albeit brief) appearance later on, when we discuss electrostatics and grounding. Matter- Eater Lad, whose real name in Tenzil Kim, from the planet Bismoll, whose inhabitants have evolved the ability to chew and digest any and all types of solids, from stone to metal to plastic, is not really relevant to explain any important physics principles. Nevertheless, villainous foes of the Legion have discovered to their regret that no jail can hold Matter-Eater Lad (who always takes a bite out of crime). But we will see in this chapter that the most undeservedly underrated superhero is Aquaman.

Fig. 13.
Aquaman in his first comic adventure, in
More Fun Comics # 73,
punching a hole through the plates of a submarine, which is designed to withstand the pressures at the ocean’s floor.

Making his debut in
More Fun Comics # 73
back in November of 1941, Aquaman was created by artist Paul Norris and writer Mort Weisinger; the latter would go on to edit the Superman comic line in the 1950s. In this first story, a German U-boat mistakenly torpedoes a refugee ship, which had been granted immunity from harm. In order to cover up their mistake, the submarine crew prepares to sink the lifeboat carrying the passengers and crew from the refugee ship. However, the refugees are saved by the sudden appearance from beneath the ocean’s surface of a strange hero, wearing an orange top and green slacks, who then goes on to mete out justice to the German submariners. While he never achieved the popularity of Superman, Batman, or Wonder Woman, he did share with them the distinction of maintaining a monthly publication schedule even during the dark period of the mid 1950s, when nearly all of the other superhero titles went out of print. Not bad for a guy who talks to fish.

From this very first appearance in 1941, it was clear that Aquaman could breathe underwater, possessed great strength, could swim at remarkable velocities, enjoyed keen vision that enabled him to see even in the murky ocean depth,
²¹
and could communicate with fish (though in his first adventure he used plants as an intermediary to send a message to some porpoises—it would be four issues later when he gave direct orders to a sawfish). All of these skills are consistent with known properties of fluid mechanics (well, “fish telepathy” requires a little electromagnetic theory—we will hold off discussing this superpower until later on in Chapter 20).

The most striking ability of Aquaman, as well as that of Marvel Comics’ Prince Namor, the Sub-Mariner,
²²
and all the other denizens of comic books’ many distinct underwater cities of Atlantis, is the ability to extract oxygen directly underwater. Without this superpower, there doesn’t seem to be much point to being a water-based superhero. It turns out that this is the one special power that requires the smallest miracle exception from the laws of nature. Why shouldn’t Aquaman breath through water—after all, we do!

Everyone knows that drowning results when the lungs fill up with water. What is less commonly recognized is that normal breathing would be impossible without a small amount of water in the lungs. Fresh air comes in through the nose, and travels down the bronchial tube, where it is warmed to the body’s temperature and pre moistened. In fact, the air has to be at 100 percent relative humidity as it moves down the ever more finely branching tubes on its way to the alveoli—small little spherical buds where the exchange of oxygen and carbon dioxide occurs. These pockets are roughly 0.1 to 0.3 mm in diameter, smaller than the period at the end of this sentence. On the other side of the walls of the alveolar bud are the capillaries—very narrow blood vessels in which plasma and red blood cells flow to drop off carbon dioxide molecules and pick up oxygen molecules on their way to the heart. The capillaries are narrow for the same reason that the alveolar spheres are so small—to maximize the ratio of surface area to volume. Since the gas exchange takes place only through the walls of the alveoli and the capillaries, the more surface area there is, the more regions there are for possible gas diffusion to occur.

There has to be some transition for these gas molecules between the interior of the alveoli—which are connected through the bronchial tubes to the outside world—and the capillaries that carry the blood. This is provided by a thin coating of water on the interior of the alveolar surface. This water layer facilitates the transfer of gases by ensuring that the inner cell walls of the alveoli do not become dried out by direct contact with air, which would cause them to lose their functionality. Only after it is has dissolved from the gas phase to the liquid phase can an oxygen molecule diffuse through the two cell walls and get picked up by speeding red blood cells. The alveoli can be considered air bubbles in water, and we could not breathe without (a little) water in our lungs, though, just as so often in life, too much of something turns a necessity lethal. Aquaman, who lacks the gills of a fish that facilitate our finny friends’ oxygen extraction directly from the surrounding water, must have some sort of superpower adaptation that enables him to continue breathing even when completely underwater.

But even this very thin water layer in the alveoli should be physically capable of causing asphyxiation. The same physics responsible for glistening dewdrops should produce acute shortness of breath, or worse. The magnitude of surface tension in the water layer is sufficient to cause the small alveolar buds to close up entirely, so that even deep breaths would not be enough to provide the necessary pressure to drive the oxygen molecules into the bloodstream. What saves us from choking on an amount of water that could not fully fill a thimble? Soap!

Surface tension is the name given to the pulling force that results from the attraction of molecules in the fluid (let’s say water) to each other. Such an attractive force must of course exist—or else the atoms or molecules in the liquid would fly away from each other as they return to the vapor state. For most liquids, this force is a relatively weak electrostatic cling (called the van der Waals attraction) that arises from fluctuating charge distributions in the molecule. The force can’t be too strong, for the water molecules must be able to move past each other and flow through hoses or fill up the volume of a container in exactly the manner that a solid doesn’t. We’ll discuss van der Waals later on, when we consider the physics that enables gecko lizards and Spider-Man to climb up walls and across ceilings.

This attractive force tends to pull the water molecules equally in all directions—it is not stronger in the up-down direction than it is in the left right direction. For water molecules in the middle of a liquid, the pull is balanced on all sides. A molecule on the surface of the liquid only feels an attractive pull from the water molecules beneath it, as the air above does not exert an upward attractive pull. These surface molecules therefore experience a net downward pull that curls the water into a perfectly spherical drop in the absence of gravity. For water on a blade of grass at dawn, condensing from the atmosphere owing to the lower temperatures in the absence of sunlight, the water adheres to the surface of the grass, and surface tension curves the top layer of the morning dew into a hemisphere. This curved surface of water acts as a lens, concentrating the early- morning sun’s rays and accounting for the glistening light of dawn before the sun rises higher in the sky and the more intense sunlight evaporates the water droplets.

This tendency of water to curve is less charming when it forces the walls of our alveoli to constrict, requiring extreme pressures to keep the air buds open. When faced with the problem of decreasing the surface tension in alveolian water in the development of our physiology, natural selection chose the same solution we employ when washing our clothing. The cells in the alveolar walls generate a substance known as “pulmonary surfactant.” The first term just refers to the lungs, while a “surfactant” is a long, skinny molecule with different chemical groups at either end. Electrostatic interactions result in one end of this molecule being attracted to the charge distributions in water molecules, while the other end is repelled by those same charges. If the long skinny molecule
²³
is fairly rigid, like a spine, then a large collection of such molecules will orient themselves so that all of the regions that are repelled by water are pointing in one direction (typically where there is a low concentration of water), while those ends that are attracted to water will extend into the fluid. The region where the surfactant molecules can satisfy both ends at the same time is at the water-air interface, with the water-attracting end inserted into the water and the water-avoiding end protruding out into the air. In such a configuration, the surfactant interferes with the water-water bonding at the surface of the water layer. This reduces the cohesive force between water molecules that was the source of the surface tension. Without pulmonary surfactants, the alveoli—essentially air bubbles in water—are unable to effectively facilitate gas exchange with the bloodstream. These crucial surfactants do not develop in the fetus until late in its gestation, which is why premature babies may suffer from respiratory distress syndrome, an often-fatal condition prior to the development of effective artificial surfactants.