by White, Mark
25. For this period, see Thor, vol. 2, #51–79 (September 2002–July 2004), reprinted in a series of trade paperbacks. Also, on the difficulties with time travel and “fixing” the past, see the chapter by Andrew Zimmerman Jones titled “Can Kang Kill His Past Self? The Paradox of Time Travel” in this volume.
26. Squadron Supreme #1–12 (September 1985–August 1986), reprinted in Squadron Supreme (1996).
27. Reynolds, Super Heroes, 77.
28. Siege #4 (June 2010), reprinted in Siege (2010).
29. Secret Avengers #1 (July 2010), reprinted in Secret Avengers Vol. 1: Mission to Mars (2011). See the chapter by Louis Melançon titled “Secrets and Lies: Compromising the Avengers’ Values for the Good of the World” in this volume on the Secret Avengers and the ethical issues faced by the covert special-ops team.
30. Captain America #619 (June 2011), reprinted in Captain America: Prisoner of War (2011).
PART FIVE
WHAT KIND OF WORLD DO THE AVENGERS LIVE IN?
Chapter 13
CAN KANG KILL HIS PAST SELF? THE PARADOX OF TIME TRAVEL
Andrew Zimmerman Jones
Jessica Jones: Is this a time travel thing? ’Cause I hate time travel things.
Iron Man: If it’s Kang, it’s a time travel thing.
Jessica Jones: See. That’s why I hate Kang.1
Ever since H. G. Wells, time travel has been a staple of science fiction and its close cousin, superhero comics. In the Avengers canon, perhaps the best-known time traveler is Kang the Conqueror, a warlord from the thirtieth century whose attempts to gain a foothold in the earlier centuries have frequently put him in conflict with the Avengers. At various times, he has shown up not only in the identity of Kang, but also as Immortus (the “Master of Time”), the Pharaoh Rama-Tut, the Scarlet Centurion, and Iron Lad (the founder of the Young Avengers). Kang’s time-hopping manipulations of the Avengers actually predate his own first appearance. In the second issue of Avengers, the Space Phantom attempts to turn the Avengers against each other, resulting in the Hulk’s departure from the team. The Space Phantom is, of course, later revealed to be a minion of Immortus, the more scholarly (and manipulative) incarnation of Kang.2
For nearly a century, scientists and philosophers alike have seriously debated whether the laws of physics, metaphysics, and logic permit time travel. The problem is that once you allow time travel, logical inconsistencies come up, which eventually transform into contradictions, which then blow up into a full-on time paradox and potential violations of physical laws.
The Science of Bending Time
Though our current scientific model of time is based upon Albert Einstein’s theory of relativity—a fact for which Hank Pym will always be profoundly jealous—the strange, ephemeral nature of time has been pondered for centuries. The philosopher and theologian Saint Augustine (354–430) mused, “What, then, is time? If no one asks me, I know what it is. If I wish to explain it to him who asks me, I do not know.”3 Augustine resolved the conflict through an appeal to a supernatural creator, but that option is not, as a rule, available to scientists. Scientific attempts to quantify the ephemeral nature of time have tended to be tied to the regular activity of a physical system, which is the basis for any sort of timekeeping device, from an astronomical calendar to a water clock to the digital chronometer in Iron Man’s heads-up display.
Einstein, however, realized that this same regularity created an issue. Let’s say that you set up a simple clock that consists of a light that points straight up. It fires a tiny pulse of light that hits a mirror one meter above it, and is then reflected back down to a detector right next to where the laser was emitted. Each cycle is a “tick” and a certain number of ticks indicates a second, and so on. One of Einstein’s greatest insights was the realization that light moved at a constant speed, so this sort of ideal clock will be perfectly precise.4 If you keep such a clock with you, you’ll always have a precise measurement of the time wherever you are.
Unfortunately, there is a problem, which becomes evident if you consider the clock in motion. And there’s no one better to choose when discussing motion than Pietro Maximoff, Quicksilver, although even he can’t move fast enough for our example without some help. So let’s assume that Quicksilver is traveling to the Shi’ar homeworld with his wife, Crystal. He sets sail on his fiftieth “birthday,” in March 2014 (based on the first appearance of Quicksilver and his twin sister, the Scarlet Witch, in March 1964’s X-Men #4).
Though the ship they’re using should have faster-than-light engines, the engines are broken, and so Pietro and Crystal are forced to travel at a speed that is very fast, but still a bit shy of the speed of light. They decide the trip isn’t worth the trouble and turn around, but they’re moving so slowly (in cosmic terms, that is) that the trip still takes a while. Quicksilver is impatient, so he pays close attention to his clock, measuring exactly 365 twenty-four-hour periods (days, if you will) between his departure and his return. He shows up on Wanda’s doorstep, ready to celebrate his fifty-first birthday!
Pietro’s sister Wanda has a clock of her own, though. (Perhaps the matching set was a gift from dear old Dad, Magneto—the master race of mutants must be punctual, after all.) If she were able to use her hex powers to keep an eye on Pietro’s clock while he was traveling, she would not see a stationary clock, but rather a clock in motion. In fact, while Pietro watches the light pulse travel only two meters (one meter up and one meter back down), Wanda sees the clock also travel almost two meters (remember, the ship’s speed is just shy of light speed) in the horizontal direction. From Wanda’s viewpoint, the pulse of light traces out two sides of an isosceles triangle with a height of one meter and a base distance just shy of two meters.
It doesn’t take Hank Pym or Tony Stark—just some basic geometry—to figure out that the path of light Wanda sees is going to be longer than the path that Pietro sees. Since the speed of light is constant, it takes longer for the clock to complete a tick for Wanda than it does for Pietro. In other words, time on the spaceship moves slower than it does back on Earth.
For the sake of this example, let’s say that Quicksilver’s clock on the ship is moving at one-twentieth the rate of Wanda’s clock. If the entire round trip took exactly one year according to Quicksilver’s clock, Wanda’s clock would say that it took twenty years. Here is the paradox: how old is Quicksilver upon his return? His birth certificate and driver’s license indicate that he was born in March 1964 and he returns in March 2034, Earth time, so it would appear to be his seventieth birthday. But from his perspective, it’s his fifty-first birthday. (Of course, in the case of Pietro, we run into further problems based on his superspeed metabolism and various aging issues related to extraneous time travel, but for the sake of this example, those can be ignored, as can his timeless Steve Martin–like hair color.)
What’s intriguing about this example is that, mutant superpowers aside, it’s completely consistent with the known laws of physics. In fact, it’s a classic case known as the twin paradox (appropriately enough). The only reason we don’t regularly run into this problem is the engineering challenge of building a near-light-speed spaceship. But smaller-scale experiments, such as those involving the lifetime of unstable particles before they decay, have absolutely confirmed this effect as predicted by Einstein. So it’s not just an imagined effect of our hypothetical clocks. Real physical systems can actually experience time in different ways, depending on how they’re moving relative to one another.
Breaking Time
The twin paradox is not really a logical paradox but rather an example of our normal language being unprepared for an unusual situation. Our intuition fails us, but there are no real scientific ambiguities. It’s just a question of what point of reference should be used when defining aging. Nonetheless, it is a kind of time travel, in that it enables Pietro to travel ahead twenty years in Earth time while only aging one year himself.
For “real” time travel, the sort that allows Kang to shunt
around the timestream battling the Avengers in ancient Egypt, the wild west, and modern-day Manhattan, the trip can’t be one-way—he has to be able to travel back in time as well as ahead. So, is there any scientific way to travel backward in time? Actually, there are a few, in theory, at least (or perhaps I should say, at most).
To understand these theories, it’s important to realize that Einstein’s theory of general relativity describes a way to model how objects move within the universe once you’ve decided what that universe is like, based on parameters such as overall energy and matter density. The problem of defining the parameters of the theory and determining what weights to give them is an experimental challenge that physicists have been working on for nearly a century. On the bright side, these puzzles resulted in all sorts of unexpected findings such as dark matter and dark energy—okay, maybe not such a “bright” side—that aren’t directly relevant to our discussion of time travel.
Time travel discoveries are of an entirely different sort, because they are (so far) mathematical discoveries only. Mathematicians and theoretical physicists tend to approach theories as if they’re a What If comic book, creating hypothetical universes that fit certain criteria and then figuring out what the theories tell them about such a universe. This approach can result in some solutions that are mathematically feasible even though no experiment has ever revealed them. (This process, in turn, gives experimenters some ideas of what to be looking for, so it’s a useful exercise.)
For example, in 1937, physicist W. J. van Stockum asked us to imagine that there was an infinitely long cylinder spinning in empty space. When he used the mathematics of general relativity to analyze this hypothetical situation, he discovered that it was possible to have an object whose path started in one location in space and time and ended at the same location. (Such a path is called a closed timelike curve.) But unless you’re visiting Galactus’s barber (with the awesome power of the Silver Scissors), where are you going to find an infinitely long spinning cylinder?
In 1949, Einstein’s friend and colleague, the mathematician Kurt Gödel, considered a more realistic scenario: what if the universe itself is spinning? Gödel discovered that such a universe—if it were spinning fast enough to avoid a collapse—would also result in closed timelike curves. Though Gödel himself was concerned about the possible paradoxes resulting from such a universe, there were two approaches to take in addressing those concerns: deny the physical possibility of the closed timelike curves, or deny the possibility of the paradoxes.
Einstein took the first. Since Gödel’s model required a spinning universe, Einstein concluded that it probably didn’t spin. (This tactic turned out to be valid because, to date, all evidence indicates that the universe is not spinning. Whew.) It’s possible also to take the second approach, maintaining that time travel can exist, but that paradoxes cannot. On this view, the closed timelike curves create a loop, but the events on that loop are set in stone. If something happened in Kang’s past and Kang goes back, then he was already there and he can’t change what happened. The “future” Kang visiting his own past is also part of that past, and the events unfold in one and only one way, no matter what sort of time travel is involved.
Building a Time Machine
So we’re left with our initial question: could Kang kill himself? Before we can explore that question in depth, we need to go one step further in the scientific realm: we have to build a time machine. In 1983, astronomer (and TV star) Carl Sagan sought help for his novel Contact, and in so doing contributed to a “realistic” notion for a time machine. To help, the physicist Kip Thorne came up with new solutions to general relativity that avoided a lot of problems but created entirely new ones.
The idea was built around a wormhole, which is a portal that opens in two locations and allows something going in one side to come out the other (like a tunnel). Such things are possible in physics (they’re called Einstein-Rosen bridges), but they’re believed to be highly unstable, one-way tickets and buried in the center of black holes (if they exist at all). To get around this, Thorne hypothesized having enough “negative energy” and “negative matter” to create a stable two-way wormhole. On paper this works, but in reality physicists don’t have any reason to think that this stuff actually exists, and certainly not in the quantities needed to pull off this sort of stunt.
But let’s assume that Kang has negative energy and matter in sufficient quantities to create a pair of movable portals that are connected by a wormhole. Kang leaves portal A on Earth, next to Wanda’s clock, and he places portal B in Quicksilver’s spaceship as he sets off on his journey. Portal B goes with Quicksilver and experiences a year of time, ending up in March 2034. On the other hand, portal A experiences a year of time and is in March 2015. Because the two portals are connected by a wormhole, this creates a portal between March 2015 and March 2034. This certainly seems like a far clunkier method of time travel than whatever Kang employs, but it allows him to implement a nefarious plan to destroy the Avengers once and for all.
In the next issue of this epic story arc, once Kang has his two time portals, he fires a laser into portal B. The beam comes out at portal A and gets deflected by mirrors for nineteen years until March 2034, when it reflects back into portal B along with the original laser. (Or, for the impatient, just put portal B thirty seconds into the future from portal A, which would give the Avengers less time to thwart the plan.) The beam entering portal B is now twice as powerful as the laser Kang initially used. But wait: because he’s already got his mirrors all set up, the beam continues to bounce around and go into portal B yet again, resulting in a beam that is three times as powerful as the laser Kang initially used. If he does this over and over, he can end up with as much power as he needs to destroy the Avengers.
The problem is that Kang used a single laser to generate significantly more energy than he started with, which is a clear violation of the law of conservation of energy, one of the most important fundamental physical principles in our universe. It is this sort of problem that caused Stephen Hawking to propose a “Chronology Protection Conjecture.” According to Hawking, since time travel allows for the violation of fundamental physical principles, there must be some law of nature that makes it impossible to actually build any sort of time machine: “The laws of physics conspire to prevent time travel, on a macroscopic scale.”5 This is essentially the same approach taken half a century earlier by Albert Einstein in response to Gödel’s earlier closed timelike curve result: deny any potential physical reality to time travel. Not all physicists are convinced, however. Some continue to believe that time travel is consistent with the known laws of physics. Most of these physicists seem to think that the paradoxes are avoided because the closed timelike curves don’t allow you to change the past, which is another way of making history safe for historians . . . or would-be conquerors.
Closed Timelike Kang
An entire volume could be written about Kang and time paradoxes—literary agents, you know where to find me—but I’ll limit myself to three events from his checkered history that best show the immutable nature of closed timelike curves.
By the 1980s, all of Kang’s time travel and manipulations had resulted in a lot of divergent timelines where Kang existed in various forms. One version of Kang (who is often called “Prime Kang”) ends up in Limbo, from which he’s able to see the various timelines and realizes that in many of them he is absolutely inept. So he sets a plan in motion to eliminate all of the “flawed” versions of himself “before the name of Kang becomes synonymous with ‘fool’!”6 The plan is mostly successful, but just as Prime Kang declares his victory, he discovers that he was manipulated by Immortus, the Master of Time, into eliminating all the extraneous Kangs. Driven insane by the memories of the Kangs he killed, Prime Kang vanishes into the halls of Limbo.
In this scenario, there is not just one path for Kang but many divergent paths, which seems to fly in the face of the idea of a closed timelike curve. The Marvel Universe i
s known to have many parallel worlds or universes, however. So the fact that variants of Kang exist isn’t particularly troubling. Prime Kang himself explains this to the Avengers during the Destiny War: “Time-travel does not change the past—as I trust you’ve learned. If one alters the flow of events, it merely creates a new, divergent branch of the timestream, while the old one flows on.”7 In eliminating the “flawed” Kangs, Prime Kang has not altered the past (or even the future). Their actions already happened (or will already happen) in this timestream, but by killing them it just cuts down the overall number of Kangs running around.
From Kang’s perspective, the problem is that he is destined to become the scholarly Immortus, which he views as a fate worse than death. He is Kang the Conqueror, after all, and the idea of giving up the conquering does not sit well with him. The effort to thwart this fate becomes Kang’s motivation in the Destiny War. In this battle, Immortus seeks to not only prune the timeline, but to make changes that sweep through all timelines. He is successful in converting Chronopolis (Kang’s cross-timeline base of operations) into the Forever Crystal to help him “change history—and reflect those changes throughout all of the timestream.”8
