They posed the following situation: Consider a box, in which is placed a cat and a sealed bottle of poison gas, along with another, smaller box that contains one single radioactive isotope. The radioactive element has a half life of one hour, which means, according to quantum mechanics, that after one hour, there is a fifty-fifty chance that it will have decayed. A by-product of this nuclear decay is the emission of an alpha particle (otherwise known as a helium nucleus), and the bottle of poison is arranged such that it will break open if struck by this particle. So, after one hour, there is a 50-percent chance that the cat is dead, having succumbed to the poison vapors released when the bottle was struck by the alpha particle, and a 50-percent chance that the bottle remains undisturbed, leaving the cat alive and well. According to Schrödinger’s equation, prior to the one-hour time limit, the cat can be meaningfully described only as “the superposition (or average) of a dead cat and a live cat.” Once the hour has passed and the lid is opened and one looks inside, the “average cat’s wave function” collapses into one describing either a 100-percent-live or 100-percent-dead cat, but there is no way to know which will be observed before the lid is opened. If the walls of the box are transparent, you can never be sure that the light from the outside has not disturbed the decay process (recall that observing quantum systems can sometimes alter them). This interpretation has been found wanting by many physicists (despite the fact that recent experiments on entangled quantum states of light, as described in JLA # 19, the latest version of the Justice League of America, suggest that this is exactly what does occur), and a great deal of thought and argument has gone into attempting to resolve the intellectual unpleasantness associated with Schrödinger’s Cat. One provocative solution to this problem, described below, enables the Flash and Superman to travel to alternate Earths.
In 1957, the physicist Hugh Everett III argued that when the cat is sealed in the box, two nearly identical parallel universes exist: one in which at the end of the hour the cat is alive and another in which it is dead. What we do when we open up the box does not involve collapsing wave functions, nor is the cat 50-percent dead and 50-percent alive before we take a look. Rather, all we do at the end of the hour is determine which of the two universes we live in—one where the cat lives or one where the cat dies. In fact, for every quantum process for which there are at least two possible results, there are that many universes, corresponding to the different possible outcomes. The two Earths reflecting the two possible outcomes of a particular quantum event will each evolve in different ways, depending on the myriad additional quantum events that occur following this initial branching point. If the bifurcation of the Earths occurred recently, then a particular Earth may be similar to our own world. If the separation occurred a long time ago, then during the intervening time, there would be many opportunities for subsequent quantum events to have outcomes different from what was observed in our world. The history of this second Earth may be very much like ours, then, but there is also the possibility of dramatic differences.73
Hence, quantum theory provides a physical justification for both the “What If?” tales in the Marvel universe and the alternate Earths in DC comics. On one Earth, Jay Garrick inhaled “hard water vapor” in a chemistry lab accident, gaining the gift of superspeed with which he fought for justice as the Flash with his teammates in the Justice Society of America. On another Earth, police scientist Barry Allen was doused with an array of chemicals while simultaneously being struck by lightning, leaving him with the gift of superspeed, with which he fought for justice as the Flash with his teammates in the Justice League of America. On another Earth a super-speedster committed crimes as the evil Johnny Quick with his teammates in the Crime Syndicate of America. There are in principle an infinite number of Earths, corresponding to all possible outcomes of all possible quantum effects, though a basic tenet of this theory is that ordinarily there can be no communication between these multiple alternate Earths. Ordinarily. Apparently, for someone able to vibrate at superspeed like the Flash, travel between these many worlds could occur as often as readers kept buying such stories.
To physicists, Hugh Everett III’s proposal led to a very different crisis of infinite Earths. The many-worlds solution to the Schrödinger’s Cat problem represented to most physicists an example of the cure being worse than the disease. Nevertheless, there is nothing logically or physically inconsistent with this theory, and no one has been able to prove that it is incorrect.
Physicists who considered it intellectually unsatisfying to say that a complete theory of nature can predict only probabilities were not heartened by the notion that the theory actually described an infinite number of alternate universes. The “ many-worlds” model has been considered the crazy aunt of quantum theory since its publication, and has been locked in the metaphoric attic until very recently. It was never taught to me, for example, when I studied quantum mechanics in college and again in more detail in graduate school. I discovered the “many-worlds” model completely by accident when, as a graduate student, I came across a copy of Bryce DeWitt and Neill Graham’s 1973 book The Many-Worlds Interpretation of Quantum Mechanics, left abandoned in a graduate student’s office. In a successful attempt to procrastinate doing my homework, I picked up this strange book, began reading it, and thereupon learned that somewhere there was another James Kakalios who was actually finishing his assignment on time (not that this knowledge did me any good).
Though few physicists give the “many-worlds” model the time of day, there is one class of theoretical physicists, some of whom are supporters of this idea: string theorists.
WHY SUPERMAN CAN’T CHANGE HISTORY
In the years following the development of the Schrödinger equation, scientists have developed techniques to describe how the electron’s matter-wave interacts with quantum versions of electric and magnetic fields (a process called “Quantum Electro-Dynamics” or QED) and how the matter-waves of quarks inside a nucleus behave (a process termed “Quantum Chromo- Dynamics” or QCD). A remaining goal of theoretical physics is to understand how to unite the physics of large-scale massive objects, governed by gravitational physics, with the quantum world. There is a perfectly good theory for gravity, namely Einstein’s General Theory of Relativity. There is an excellent theory to describe the quantum nature of electrons (QED). Combining these theories into one coherent whole has proven beyond the abilities of any scientist up until now. The closest that theorists have come to a quantum theory of gravity is something called “string theory.”
A gross oversimplification of string theory is that it suggests that matter is itself a wave, or rather a vibration of an elemental string, and that these “strings” are the basic building blocks of everything in the universe. In its current state, many physicists are skeptical about string theory. Their first objection is that, in order for the equations to balance, string theory works only in eleven dimensions (ten spatial and one time). This is somewhat awkward because, as near as we can tell, we live only in three spatial dimensions, and no one has ever encountered additional dimensions.74 To address this discrepancy string theorists have suggested that there really are eleven dimensions, but seven of these spatial dimensions curl up into little balls, with a diameter less than a billionth trillion trillionths of a centimeter, a length scale labeled the Planck length, though some versions posit the existence of very large dimensions. Another drawback of string theory is tied to this extradimensional notion: Probing length scales so small requires correspondingly higher energies than current and next-generation particle accelerators can achieve. Without the verification provided by experimentation, the only criterion to determine whether the equations are on the right track is mathematical elegance. This may be dangerous; while it is true that the equations of classical mechanics (electricity and magnetism) and quantum mechanics do indeed have a certain mathematical beauty, there is no a priori reason to believe that nature really cares whether we find the equations pretty or not. Nevertheless, string
theory is presently the only likely candidate for a quantum theory of gravity, and only further study will determine its success.
Physicists investigating quantum gravity have invoked the many-worlds interpretation in order to resolve logical inconsistencies in their calculations involving time travel. Recently, some scientists have claimed that time travel is not physically impossible, though it is highly unlikely to ever actually be accomplished. The problem with time travel into the past is set forth in the famous “grandfather paradox.” Essentially, if one could indeed travel back in time, it would be possible to murder your grandfather when he was a young man, before your own father was conceived. In this way you would prevent your own birth, but the only way you could have prevented it is if you had first been born. In order to find a way around this conundrum, modern theoretical physicists have dusted off Hugh Everett III’s many-worlds interpretation. If there are indeed an infinite number of alternate parallel universes, then (the theorists argue) when you travel backward in time, the severe distortions in space-time necessary to make this journey would also simultaneously send you to a universe parallel to your own. You are therefore free to kill as many grand-parents as ammunition allows, without fear of altering your own existence, because your own grandfather is safe in the past in your own universe, undisturbed by the havoc you are wreaking in alternate past worlds.
These modern theoretical notions were actually anticipated in the 1961 adventure “Superman’s Greatest Feats” in Superman # 146. In this story, Superman agrees to travel into the past as a favor for Lori Lemaris, a mermaid from the sunken city of Atlantis with whom he had a “special relationship” (while she was a girl and was his friend, Lori was not Superman’s girlfriend). Lori beseeches Superman to prevent the sinking of Atlantis, which occurred millions of years ago. Superman argues that all of his previous attempts (presented in earlier issues of Action Comics and Superman) to change history have failed, but Lori’s pleading (and what appear to be bedroom eyes) convinces Superman to give it a try. Given that it takes great effort and a velocity larger than 1,100 feet per second to break the sound barrier (the effort, as discussed in Chapter 4, is due in part to the work one must do to push the air out of his way), it was proposed in DC comics that with an even-greater effort and a much faster velocity, one could pass through the “time barrier.” (Both the Flash and Superman, each capable of these necessary speeds, could travel back and forth through time as their story lines required.) Superman thus zooms to at least 8,000,000 B.C.E. and reaches nearly the exact moment when the advanced civilization of Atlantis, which resides on a small island off the shore of what appears to be a coastal resort, is about to succumb to “giant waves caused by a colossal undersea earthquake.” Superman races to another island a safe distance from the undersea quake, which is the home to another advanced civilization. Why we have never heard about this other ancient civilization is not addressed. Superman borrows some “strange metal” from buildings about to be torn down on this other island and fashions an enormous crane with which he lifts the entire island of Atlantis, depositing it onto a third, secure deserted island, where it is spared by the earthquake. (Let’s not even get into what this “strange metal” could possibly be composed of that would give it a tensile strength sufficient to lift an island.)
Fig. 32. Superman travels through time and saves Abraham Lincoln from being shot by John Wilkes Booth. Or does he?
Amazed that, unlike all previous attempts, he was able to successfully change the course of history, Superman decides to make various pit stops on his return trip to his own time period, using this opportunity to “fix” various historical events. He saves the Christians from being eaten by lions in the Roman Colosseum,75 takes Nathan Hale’s place as he is about to be executed by the British, prevents Custer’s massacre at Little Big Horn, and drops by Ford’s Theater on April 14, 1865. As shown in fig. 32, as John Wilkes Booth is about to assassinate President Lincoln, he utters “Sic semper—Ulp!” as hands that can crush diamonds close upon his pistol. Superman is now like a kid in a historical candy store, and decides to try to save the population of his home planet, Krypton. Because he loses his superpowers under the red light of Krypton’s sun, Rao (by this time the explanation for his amazing abilities had been attributed to Earth’s yellow sun), Superman decides to build a fleet of spaceships from sunken Earth naval vessels and send them to Krypton in order to enable everyone to escape to another world. Using his telescopic vision, he watches his parents disembark on a new planet with an infant Kal-El. At this point Superman realizes that he has stumbled upon a paradox, for if his parents never sent him to Earth as a baby, how is he able to save them now?
Returning to his present, in 1961, the Man of Tomorrow is sur prised to discover that history books are unchanged, shown in fig. 33. Lincoln was indeed shot at Ford’s Theater and Nathan Hale and General Custer are similarly described suffering their Superman-less fates. Superman can’t understand how this can be, since “surely, the [history] books are truthful.” Ahem. Retracing his path through the time stream, Superman comes across an alternate Earth (fig. 34), in which the history books give proper credit to Superman’s role in correcting the past’s “mistakes.”
Fig. 33. Superman, from the same story as fig. 32, now realizes that history has remained unchanged despite all of his time-traveling “Greatest Feats.”
Alas, Superman discovered in 1961 what theoretical physicists have rediscovered in 2001—that time travel is only possible via the many-worlds interpretation of quantum mechanics. Superman did indeed accomplish these amazing feats, altering the course of history—but in an alternate universe, not in his own (see fig. 34). A similar phenomenon occurs in the Marvel Comics Avengers # 267, where the evil time lord Kang the Conqueror is revealed to have single- handedly created a vast number of alternate Earths as a by-product of his frequent time-traveling in order to defeat his superhero foes. Still another example of comic books being ahead of the physics curve.
Fig. 34. Superman in 1961 discovers what quantum theorists have only recently hypothesized—that travel through time must of necessity also involve transport to alternate, parallel universes.
23
THROUGH A WALL LIGHTLY—TUNNELING PHENOMENA
IN ADDITION TO BEING ABLE to run at amazing speeds, the Flash is said to possess total control over every one of his molecules’ motions. This vibratory control was put to use in Flash # 116, Flash # 123 (see fig. 30), and many times since. Matching his body’s vibrations to the vibrational frequency of the atoms in a wall, it was argued by the writers of Flash comics that he could pass through a solid wall without harm to either himself or the wall. However, it is not true that the only reason we cannot walk through solid walls is that we vibrate at a different frequency than the atoms in the wall. As discussed earlier, the average rate at which our atoms vibrate is simply a reflection of our temperature. Our bodies are typically roughly within 40 percent of the temperature of a wall, so our atoms’ vibrational frequency is already pretty well matched to those in the wall.
Nevertheless, there is a quantum mechanical phenomenon termed “tunneling” that predicts that an object, under the right circumstances, can pass through a solid barrier without disturbing either the barrier or itself. This very strange prediction is no less weird for being true. In this way quantum mechanics informs us that electrons are a lot like Kitty Pryde of the X-Men, who possesses the mutant ability to walk through solid walls (as shown in fig. 35), or the Flash.
Schrödinger’s equation enables one to calculate the probability of an electron moving from one region of space to another even if common sense tells you that the electron should never be able to make this transition. Imagine that you are on an open-air handball court with a chain-link fence on three sides of the court and a concrete wall along the fourth side. On the other side of the concrete wall is another identical open-air court, also surrounded by a fence on three sides and sharing the concrete wall with the first court. You are free to wand
er anywhere you’d like within the first court, but lacking superpowers, you cannot leap over the concrete wall to go to the second court. If one solves the Schrödinger equation for this situation, one finds something rather surprising: The calculation finds that you have a very high probability of being in the first open-air court (no surprise there) and a small but nonzero probability of winding up on the other side of the wall in the second open-air court (huh?). Ordinarily the probability of passing through a barrier is very small, but only situations for which the probability is exactly zero can be called impossible. Everything else is just unlikely.
Fig. 35. A scene from X-Men # 130, showing Kitty Pryde (not yet a member of the X-Men) as she employs her mutant ability to walk through walls to sneak up on the White Queen of the Hellfire Club.
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