The Physics of Superheroes: Spectacular Second Edition (22 page)

In the more recent
JLA # 89,
the Flash has to move the entire population of 512,000 men, women, and children in Chongjin, North Korea, away from the imminent blast of an atomic bomb in a fraction of a second. In order to accomplish this feat, he must move at speeds very close to the speed of light. The relativistic consequences of his high speeds are alluded to once he has saved the town and collapses to his knees on a hilltop. As described in a caption box, “as his body sloughs off the screaming aftereffects of near light travel, eyes of almost infinite mass turn towards the blaze engulfing Chongjin.” Of course, to the Flash, he is stationary and it’s the rest of the world that moves and gains mass. By the way, it was the realization that an increase in the kinetic energy of an object is directly connected to a rise in its mass that led Einstein to derive E = mc
²
.

Fig. 17.
The Flash, attempting to run at light-speed, discovers that he becomes heavier the faster he runs in
Flash # 132.
Is this a textbook illustration of Einstein’s Special Theory of Relativity?

If nothing can travel faster than the speed of light, then how does the Flash’s Cosmic Treadmill allow him to move forward or backward through time? I’m sad to say that time travel doesn’t work in a reversible manner. The closer an object’s velocity comes to the speed of light, the slower time appears to pass, as regarded by a stationary observer. As will be discussed in a moment below, there is a barrier (I suppose one could call it a “time barrier”) associated with the change in mass with velocity that prevents any object from accelerating up to and beyond the speed of light. So time will appear to slow, but will never move backward. However, it is true that time travel into the future, in great leaps rather than a second at a time, is possible, if one can move fast enough.

In the
Legion of Superheroes # 16 (Vol. 5),
published in 2006, Supergirl from the twenty-first century suddenly flies a thousand years into the future. She had been pursuing an alien missile, sent at great speed by a race of would-be world conquerors to destroy the Earth. This missile was traveling at near light-speed, and the Maid of Steel had been chasing it for three solid days. After finally catching and destroying the missile, she meets a collection of teenage superheroes in the year 3006, the aforementioned Legion, and winds up joining them on a series of adventures. Supergirl and the Legion periodically express puzzlement over how she wound up a thousand years later from when she began chasing the missile. The comic eventually explained her time displacement as arising from her having crossed the path of a “zeta beam,” which apparently can move you dramatically forward in time. But Einstein’s Special Theory of Relativity provides a more natural explanation.

In a reference frame moving along with Supergirl, three days elapse as she chases after the missile. But from her point of view, she and the missile are essentially stationary, and the rest of the universe is moving past her at great speed. If the universe’s velocity, relative to Supergirl, is close to the speed of light, she will observe a dramatic time-dilation effect. Using Einstein’s equations, if Supergirl’s velocity were 99.9999999963 percent of the speed of light, then a journey that she experiences as lasting three days would, for stationary observers on the Earth, take one thousand years. When she eventually slowed down and stopped, she would find herself a thousand years ahead of when she began. There is thus a physically valid way to travel into the future, with the caveats that (1) it would require extreme amounts of energy for an object of any real size to be accelerated to such a velocity and (2) it is a one-way trip, and flying backward won’t send you back in time. (Eventually the “zeta radiation” wore off, sending Supergirl back to the twenty-first century, enabling her to continue having adventures in her own comic book.)

But what about Superman, who frequently travels back in time by flying at great speed? The Warner Bros. 1978 film
Superman: The Movie
included a scene where, in order to undo the effects of a devastating earthquake (particularly Lois Lane’s death), the Man of Steel flies around the Earth so fast that he reverses the direction of time. Is this at all possible? Close examination of the scene in question, estimating the height above the Earth that Superman is flying, calculating the distance of an orbit and counting the number of circuits completed and the time he takes doing so, we conclude that Superman is indeed traveling at or faster than the speed of light! But that alone won’t save Lois Lane. Traveling that fast, he would jump forward into the far future, as his cousin did in the Legion of Super Heroes story, and might be in time to help some distant descendant of Ms. Lane, but not be able to save Lois herself.

While the Flash did not have to worry about length shortening (technically referred to as “Lorentz contraction”) too often, the slowing of time, or “time dilation” nearly cost him his secret identity. While the Scarlet Speedster is the fastest man alive, one of the quirks of his secret identity is that his alter ego, Barry Allen, is perennially late for his appointments. Often his fiancée, Iris West, would complain about Barry’s tardiness and wish he were more like the Flash, not realizing that they were one and the same. As fate would have it, Iris’s father would also notice Barry’s habitual lateness, and as described in “Slowdown in Time” in
Flash # 141,
was very intrigued by the fact that Barry’s watch always seemed to run slow. For Iris’s father was physics professor T. H. West, and he suspected that Barry’s watch was running slow because of time dilation effects arising from his superspeed crime-fighting exploits as the Flash. Spotting a robbery in progress, he called Barry, reported the crime underway, and asked Barry to synchronize his watch. Knowing that the Flash would have to run at great velocities to catch these criminals, he intended to meet up with Barry later on and compare the times on their watches. And it would have worked, too—had Barry not reset his watch before meeting with Professor West. Tipped off by the strange request to synchronize watches, as the story concludes, Barry thinks: “As a scientist myself I’m also familiar with Einstein’s Theory of Relativity—and the effect of ultra-speed on clocks!” Sometimes even physics professors fall short when they try to outthink the Viceroy of Velocity!

In theoretical physics, there is one thing that can travel faster than the speed of light: particles termed “tachyons” that in fact can never travel slower than the speed of light. Under certain circumstances, they can appear to travel backward in time (which proved useful for Adrian Veidt in
Watchmen,
who employs tachyons to obscure the precognition abilities of Dr. Manhattan). Tachyons were proposed as a test of certain consequences of the Special Theory of Relativity. As far as we know, they do not exist, and more importantly, even if they were as common as crabgrass it doesn’t appear that they can interact with our physical world, in which no object can move faster than the speed of light. The Flash may travel backward and forward in time using his Cosmic Treadmill, but its only real value is in providing the Scarlet Speedster with a cardio workout.

The fact that Superman and the Flash would move through time thanks to their superspeed powers has not escaped the attention of physicists. Following the printing of the first edition of this book, a story was relayed to me concerning Superman’s meddling with the space-time continuum. Back in the 1950s a group of physics majors at M.I.T. wrote to Mort Weisinger, the editor of Superman comics at the time. They complained that a recent issue had shown Superman flying faster than the speed of light, in direct contradiction to Einstein’s theory. What did he have to say about that? To which Weisinger allegedly replied: Einstein’s is only a theory—Superman is fact!

SECTION 2

12

THE CENTRAL CITY DIET PLAN—
CONSERVATION OF ENERGY

THE FLASH MAY BE ABLE to run across the ocean and pluck bullets from the air, but a more pressing question is: How frequently does he need to eat?

The short answer is, a lot! Before we determine exactly what his caloric intake must be as he rounds up his rogue’s gallery of supervillains in Central City, we address the more basic question: Why does he need to eat? What exactly does food contain that is essential for any activity, whether running, walking, or just breathing while sitting still? And why do we only obtain these qualities from organic matter, and not from rocks or metal or plastic?

The Flash eats for the same reason we all do: to provide raw materials for cell growth and regeneration, and to provide energy for metabolic functioning. At birth, your body contains a certain quantity of atoms that was insufficient to accommodate all of the growth that will occur during your lifetime. As you grew and matured, you needed more atoms, typically provided in the form of complex molecules that your body would break down and convert into the building blocks necessary for cell replacement and growth. As noted in our discussion of the explosion of Krypton, all of the atoms in the universe—including in the food we ingest—were synthesized via nuclear reactions in a now long-dead star where hydrogen atoms were squeezed together to form helium atoms, helium fused to form carbon, and so on. An additional by-product of these fusion reactions in our sun provides the second essential component of the food we eat. Matter- Eater Lad of the Legion of Super-Heroes may be able to subsist by consuming inert objects such as metal or stone, and the cosmic menace Galactus must consume the life-energy of planets, but for us, for the most part, the food we eat must have been previously alive. Only such foodstuffs provide the necessary component for life, as mysterious as its name is mundane: energy.

The use of the word “energy” is so common that it is unnerving to realize how difficult it is to define without using the word “energy,” “heat,” or “work” in the explanation. The simplest non-mathematical definition is that “energy” is a measure of the ability to cause motion. If an object is already moving, we say it possesses “kinetic energy,” and it can cause motion if it collides with something else. Even if it is not moving, an object can possess energy, such as when it is pulled by an external force (for example, gravity) but is restrained from accelerating (say, by being physically held above the ground). Since the object will move once it is let go, it is said to possess “potential energy.”

All energy is either kinetic or potential, though depending on the circumstances, a mass can have both kinetic and potential energy, such as when Gwen Stacy fell from the top of the bridge in Chapter 3. When she was on the top of the bridge, she had a large potential energy, as gravity could act on her over a long distance, from the top of the tower to the river below. But her motion was constrained, as the bridge was holding her up. When she was knocked off the tower, this constraint was removed, and the force acting on her (gravity) then began her acceleration. As she plummeted, she had a shorter and shorter distance over which to continue falling, so her potential energy decreased. This energy didn’t disappear, but rather her large potential energy at the top of the bridge was converted to ever-increasing kinetic energy as she fell faster and faster. At any given point in her fall, the amount of kinetic energy she gained was exactly equal to the amount of potential energy she lost (ignoring the energy expended in overcoming air resistance). If she had struck the water at the base of the bridge, her potential energy relative to the ground would have been zero (once at the base of the tower she has no more potential to fall), while her speed and, hence, kinetic energy would have been at its greatest. In fact (again ignoring air drag) her kinetic energy at the base would have been exactly equal to her large potential energy at the top of the bridge when she started to fall. This kinetic energy is then transferred to the water, which supplies a large force that changes her high velocity to zero, with a similar dire result as when she was caught in Spider-Man’s webbing, as described in Chapter 3.