The Physics of Superheroes: Spectacular Second Edition (25 page)

It’s the power and not the energy that determines why we don’t have flying cars, despite the fact that we are presently well within the “far future” as imagined by Silver Age comic books of the 1950s and 1960s. Consider Nite Owl’s flying “Owlship” from the 1986 graphic novel
Watchmen.
Nite Owl (technically Nite Owl II), in the novel by Alan Moore and Dave Gibbons, is a knockoff of the Charleton Comics superhero Blue Beetle, who in turn was a knockoff of the DC Comics hero Batman. Dan Dreiberg in
Watchmen
used his inheritance from his banker father to outfit himself with a brownstone with a large basement in which he stored an array of gadgets, specialized superhero costumes (for fighting evildoers in such extreme environments as underwater, in the Arctic, and in a radioactive hot zone), a collection of trophies and mementos from memorable cases, and a large flying airship called
Archimedes
(or
Archie
for short). The airship, a large, rounded transport about the size of a minivan, is modeled on the Blue Beetle’s flying beetle airship—and uses the same mechanism to achieve flight: imagination.

Archie
in
Watchmen
has no visible means of levitation or thrust, and can hover in the air during a daring rescue of stranded citizens trapped in a tenement fire, or fly from New York City to Antarctica. It takes a lot of power to accomplish this. Earlier we considered the potential energy of an object raised a distance h above the ground. We determined that the potential energy (say, of Gwen Stacy on the top of the George Washington Bridge) is described by the expression mgh, where m is the mass and g is the acceleration due to gravity. The larger the weight of an object, the more Work one must do to raise it against gravity to a height h.

The full-scale model of the Owlship constructed for the Warner Bros. 2009 film
Watchmen
weighed an impressive four tons (the imaginary airship has to be strong to withstand the guards’ gunfire as they break Rorschach out of prison). Lifting such a heavy object one eighth of a mile, so that it could fly above the towers of New York, raises its potential energy by more than seven million kg-meter
²
/sec
²
. That’s a lot of energy, but more importantly, since the Owlship is just suspended in thin air, we must expend this amount of energy every second to keep it levitated. The rate at which the Owlship uses energy when simply hovering in the air, 200 meters above the ground, is 7,200 kiloWatts, or 7.2 megaWatts (where a megaWatt is a million Watts). If we wish to fly the
Archimedes
to some other location, then we need to provide kinetic energy as well, and this will add to our power needs. At a uniform cruising speed of 700 miles per hour, for long distance travel at 30,000 feet, the total power needed to fly
Archie
is over 500 megaWatts. A trip from New York to Antarctica would therefore require more than 180,000 gallons of gasoline!
⁴⁰
The
Watchmen
graphic novel required a significant suspension of disbelief when it came to the superpowered Dr. Manhattan, but perhaps the biggest miracle exception from the laws of nature involved the energy supply for Nite Owl’s flying ship.

The Owlship as drawn by Dave Gibbons in the 1986 graphic novel displays no visible signs of a propulsion system. The airship in the 2009 film version has some jet thrusters added underneath and to the rear of the transport, to acknowledge some mechanism by which it flies. Personally, if I had designed and constructed a flying ship that could hover and fly for more than thirteen hours at the speed of sound using a novel lightweight and highly efficient energy source, I would not be sitting naked in my underground Owl Cave, moping about my former crime-fighting career. Rather I’d be too busy counting the kajillion dollars a day I would earn by licensing this process.

In order to run, the Flash needs the energy stored in food, which is locked up in complex molecules. We have described this energy as similar to the potential energy of a tower of blocks that plants stack, expending Work. We transform this stored energy—after first consuming the plants—into kinetic energy when the tower is knocked over. But what is the trigger to topple this tower? How does the tower know when the cell needs the energy to be released? There’s a lot of biochemistry that goes into the release of energy by the mitochondria in a body’s cells, but the essential step involves a chemical reaction of oxygen going in and carbon dioxide coming out. Without oxygen intake, the stored energy in the cell cannot be unlocked, and there’s no point in eating. The faster the Flash runs, the more kinetic energy he manifests, the more potential energy stored in his cells he needs to release, and the more oxygen he needs to breathe. We’ve already discussed the fact that he would need to eat a staggering amount of food in order to account for the kinetic energy he routinely displays. What about his oxygen intake? Would the Flash use up all of the Earth’s atmosphere as he ran?

To answer this question, we first need to know how much O
₂
the Flash uses when he runs a mile. The volume of oxygen used by a runner will depend on his or her mass, and has been measured to be about 70 cubic centimeters of O
₂
per kilogram of runner per minute, for elite athletes at a pace of a six minute mile. Taking the Flash’s mass to be 70 kg, he then uses nearly 30 liters of O
₂
for every mile he runs (a liter is one thousand cubic centimeters, a little under a quart). Let’s assume that this rate of O
₂
use remains the same even for much higher speeds. Thirty liters of O
₂
contains under a trillion trillion oxygen molecules, and at a speed of ten miles per second, this means that the Flash inhales about a trillion trillion O
₂
molecules every second. That sounds like a lot, but fortunately there are many more O
₂
molecules in our atmosphere than that. A lot more. In fact, very roughly, the Earth’s atmosphere contains more than ten million trillion trillion trillion O
₂
molecules. So even at a rate of consumption of one trillion trillion molecules per second, he would have to run this fast (10 miles/sec) and breathe at this rate continuously for more than 100 billion years before he exhausted our oxygen supply. The faster he ran, the quicker he would use up our air, but even running at nearly the speed of light (which he is capable of, but doesn’t do very often) it would take him more than two million years of continuous running and breathing at this rate to exhaust the atmosphere. So, at least regarding this aspect of his superspeed, we can breathe easier.

The Earth’s atmosphere may be safe, but of course this assumes that the Flash is able to breathe at all while he runs—at several hundred miles per hour, would he be able to even draw a deep breath? Fortunately for the Scarlet Speedster, he carries a reservoir of air with him whenever he runs. In
Flash # 167,
this region of stationary air (relative to the Flash) is described as his “aura,” while in fluid mechanics it is termed the “no-slip zone.” Whatever you call it, it’s the reason golf balls have dimples.

Try this simple physics experiment at home: Turn on the cold water in your bathroom sink, but only barely open the valve. For the best results, first remove the aerator in the faucet. When the water is just barely coming out, you may see it move very smoothly from the faucet, with the appearance of a polished cylinder, wider at the faucet outlet and tapering slightly due to surface tension. If you ignore the sound of the water splashing in the basin, it’s difficult to tell that the water is moving at all, that it isn’t actually a rigid structure. This type of water flow, where all the water molecules are moving smoothly in the same direction, is termed “laminar flow.” At the opposite extreme, turn the valve all the way open. The water churns and swirls out, moving in different directions and with a wide range of speeds. This type of water flow is termed “turbulent.” Naturally, if you want to get water through a pipe in the most efficient manner possible, you would like the flow to be laminar, where all water molecules are moving in the same direction down the pipe, rather than turbulent, where vortices and swirls by necessity mean that some water molecules are moving against the flow.

Even in laminar flow through a pipe, all the molecules may move in the same direction, but they won’t all have the same speed. Those molecules at the outer edge will collide with the pipe’s walls, transferring their kinetic energy to the pipe (which is rigid, so that the pipe warms up a bit but doesn’t move) and coming to rest. Right next to the pipe’s walls is a thin layer of water that is not moving. Water next to this non-moving layer loses some of its kinetic energy, but not all, because unlike the atoms in the pipe, the water molecules in this “no-slip zone” can move. In the next ring closer to the center of the pipe, the water is moving a bit faster still. So, even in uniform laminar flow, there is a continuous series of concentric rings, each ring moving progressively faster than the adjacent ring. The water dead center in the pipe moves the fastest of all. In laminar flow, all rings are uniform, while in turbulent flow there is chaotic motion across the width of the pipe.

The situation is mirror-reversed for a moving pipe being pulled through stationary water. The water closest to the pipe’s walls is dragged along with the pipe, the water right next to this ring moves a little slower, and so on. But in either case, for either the water moving through the pipe or the pipe moving through the water, the water right next to the pipe is stationary, relative to the pipe. As long as the flow is laminar, then right next to a moving object, there will be a thin layer of air (the arguments for a fluid such as water apply for a fluid such as air, as well) that is not moving relative to the object. Just as in the example of the water faucet, this laminar no-slip zone is more robust the slower the motion is through the fluid. At too high a speed, the transfer of energy across concentric rings becomes disordered, and turbulence sets in. An object moving at a given speed must expend more energy generating turbulent flow than if the flow is laminar. Recall in Chapter 6 that dolphins shed skin cells in order to break up turbulent vortices in their wake, enabling them to swim at great speeds.

This is one reason why golf balls have dimples. The bumps on the golf ball decrease the cross-section of the turbulent wake behind the ball moving at higher speeds. In a crude sense, the dimples reduce the drag on the ball, as less energy is lost in the smaller turbulent wake. This effect was discovered accidentally. In the mid 1800s, golf balls were smooth, solid spheres of gutta-percha gum. It was empirically noted by golfers that old, scuffed-up balls with scratches and dings went farther for a given swing than brand-new, smooth balls. Experimental study and a theoretical understanding of fluid mechanics led to an optimal design of dimpled golf balls.

What’s good for a golf ball is good for the Flash. As the Scarlet Speedster runs, the layer of air right next to him remains stationary relative to his body, so he has a non-moving pocket of air that he carries around with him at all times. Even in a layer only a few centimeters thick, there are nearly a trillion trillion O
₂
molecules. This “reservoir” of air must be continually refreshed with new air from outside the boundary layer in order for the Scarlet Speedster to run for more than a few seconds at a time.

In Flash comics, the no-slip zone “aura” that surrounds the Crimson Comet not only enables him to breathe as he runs, but also frees him from other untidy consequences of fluid drag. Consider: If a meteor burns up in the atmosphere when it turns into a meteorite due to the extreme frictional forces it experiences as it pushes the air out of its way entering the atmosphere at high velocity,
⁴¹
then why doesn’t the Flash burn up when he runs at high speeds?

Flash Comics # 167
provided an answer to this question, but it was a solution that few comic fans found satisfying. According to this story, the “protective aura” the Flash gained along with his superspeed powers was provided by a “tenth-dimensional elf novice-order” named Mopee. In this story, using his magical abilities, Mopee (who bore more than a passing resemblance to Woody Allen) removed the Flash’s aura but not his superspeed. Consequently, when the Flash ran at great speeds, he would burn up due to the tremendous air resistance he encountered.

That the Flash had an imp who bedeviled him was not as surprising as the fact that the Silver Age Flash went eight years in his own comic before encountering him. In the fifties and sixties, it seemed like nearly every superhero published by DC Comics had his or her own extradimensional pest. The first such character was Mr. Mxyzptlk, a fifth-dimensional derby-wearing sprite against whose magical powers Superman was powerless. Mxyzptlk could only be forcibly returned to the fifth dimension if he was tricked into saying his name backward, after which he was unable to return to our three-dimensional world for at least three months (presumably so that readers would not grow overly tired of him and his appearances would be noteworthy). Not to be outdone by the Man of Steel, Batman had his own magical imp, named Bat-Mite, whose attempts to honor his idol, the Caped Crusader, frequently backfired and created mayhem and difficulties for Batman and Robin. J’onn J’onzz, the Martian Manhunter, had an alien sidekick named Zook, while Aquaman had an imp named Quisp. Of the seven founding members of the Justice League of America, only Green Lantern and Wonder Woman have never had a supernatural or extradimensional spirit to call their own.

It wasn’t the fact that the Flash finally acquired his own imp that upset comic-book fans, but rather that Mopee claimed to have used his magical powers to give Barry Allen his superspeed powers. The science-fiction aspects that writers John Broome, Gardner Fox, Robert Kanigher, and editor Julie Schwartz introduced into the Silver Age with the creation of the Barry Allen Flash seemed undermined by the claim that the Flash’s powers were in fact “magically” derived. Mopee never had a return engagement in Flash comics and, as far as most fans of the Silver Age are concerned,
Flash # 167
never happened. Let us speak of it no more.