by Huss, John
Time is like a freeway with an infinite number of lanes—all leading from the past into the future, however, not into the same future. A driver in lane A may crash while a driver in lane B survives. It follows that a driver, by changing lanes, can change the future.
He seems to be advocating for a view that allows many alternate futures to unfold, depending on the choices made in the present. This interpretation of the relationship between the certain present and the uncertain future is not far from a view espoused by a number of contemporary physicists.
The Many Worlds of Quantum Mechanics
The multiple-timeline version of time-travel may seem like something of a cheat—a way to sidestep the grandfather paradox in a way that permits sci-fi plots that are paradox-free without being needlessly convoluted. But it turns out that there may be some support for this vision of time from within modern physics, from a particular interpretation of the theory of quantum mechanics called the Many Worlds Interpretation.
One of the lasting philosophical issues facing physics is the question of how to interpret the probabilistic nature of quantum theory. In quantum mechanics, the behavior of subatomic particles is not described by a precise trajectory through space and time, the way that Newton’s Laws enable us to calculate the precise path of a planet around the Sun. Instead, the behavior of a subatomic particle is described by a quantum mechanical wave-function that only gives the probability of various outcomes. The question of what actually happens when a potential outcome becomes an observed result is still the source of much debate among physicists and the source of considerable confusion within popular treatments of quantum mechanics.
The most common way to deal with this transition from probability to actuality is simply to acknowledge that when we observe a quantum mechanical system, we introduce a discontinuity of sorts into our description of the situation. Before we make our observation, the theory demands that we describe a system using a wave-function which handles all of the potential outcomes probabilistically. But after we’ve observed the system, only one of the potential outcomes is actualized. So the old wave-function no longer applies, and is of no use to us. This transition is usually referred to as the “collapse” of the wave-function.
There’s another more exotic interpretation of this transition from probability to actuality, which is that all of the possible outcomes are actualized in separate universes. This so-called “many-worlds interpretation” suggests that every time there is a “choice” available at the subatomic level, the universe splits into multiple parallel versions of itself. Every possible outcome of the event is equally real in some parallel universe. This leads to an unimaginable number of universes branching out from our own every instant. Since these parallel universes are unobservable and undetectable from within whatever universe you find yourself, it’s not quite right to call this the “Many Worlds Theory.” The word “theory” suggests a scientific model which makes testable predictions, and most physicists agree that the Many Worlds idea does not. It is simply a conceptual framework designed to explain how a theory which is purely probabilistic at the microscopic scale could give rise to a universe that appears to have a single well-defined reality at the macroscopic scale. The advantage of the Many Worlds interpretation is that it de-emphasizes the role of the observer in the process, since the “collapse” of the wave-function, which seemed like something that was “caused” by the observer, never occurs in this model.
Many Worlds as Multiple Timelines
The multiple-timeline version of time travel seems to agree in its basic structure with the Many Worlds interpretation of quantum mechanics. If every choice that’s made in the universe, from the subatomic level to the conscious level, can give rise to branching alternate realities, then why shouldn’t the actions of a time traveler do the same?
The time traveler is just doing what we all do all the time anyway—making choices that lead to a particular future. The idea that there is only one such future is a side-effect of the fact that we ordinarily only get to observe one of those potential universes. But the time traveler gets to see the effect of these multiple choices directly, by traveling from a timeline where the universe unfolded in one way, traveling back in time, changing the circumstances, and seeing the universe unfold in a different way. If this picture of time travel is correct, a time traveler is as much a traveler between universes as they are a traveler between times.
Series Reboots and Multiple Universes
The idea that ours may be just one in an infinitude of parallel universes, each with its own unique history, might give some comfort to movie fans who are bothered by continuity discrepancies between the various Planet of the Apes movies. It can also help to sort out the place of later “reboots” of the series, such as Tim Burton’s 2001 Planet of the Apes, or 2011’s Rise of the Planet of the Apes (and its planned sequels), in the canon of the franchise.
What are we to make of a movie in which the intelligence of future apes is not explained in terms of years of selective breeding of apes as pets, but instead is the result of a gene therapy experiments that produce an airborne virus that causes death in humans, but enhanced brain development in apes? Rather than reject the movie entirely as being unfaithful to the original series, perhaps we can just regard this as a parallel future that exists alongside many others. If the Many Worlds interpretation of quantum mechanics is correct, perhaps every choice you make in the course of a day leads to trillions upon trillions of future universes. If so, who’s to say how many different ways there are to produce a future in which man is dominated by the apes?
9
Escape from the Paradox of the Apes
RALPH SHAIN
Pierre Boulle’s Planet of the Apes is a time-travel story. In the novel, however, we’re led to believe that it’s merely a story of space travel. French astronauts travel to a distant planet where most of the action takes place. In the 1968 movie, the misdirection is even more overt. Captain Taylor informs his fellow astronauts that they are on a planet 320 light years from Earth.
Yet both in the novel and film everything leads up to the revelation—the indelible moment when Ulysse Mérou returns to Earth seven hundred years later and is greeted by a gorilla in uniform, or in the movie when Taylor sees the ruins of the Statue of Liberty and realizes that he is on Earth.
Boulle’s novel and the 1968 movie feature one of two kinds of time travel—travel into the future or “forward time travel.” Travel into the past, or “backward time travel” occurs in the third film, Escape from the Planet of the Apes. There Cornelius, Zira, and Milo travel into the past—their past—back to the 1970s. The philosophical issues differ quite significantly for the two types of time travel and these differences are reflected in the way the stories are told.
Dr. Hasslein’s Theory Is Right
The idea of forward time travel is conceptually unproblematic. It involves slowing down one’s bodily rhythms until one is revived at some future time, akin to falling asleep or simply sitting idly as time passes. If we consider how we use the word ‘travel’, ‘travelling’ requires something more than the distance covered. We can imagine the slowing of bodily rhythms for future time travel taking place in a number of ways: through chemicals, coma, or freezing. The long time periods space travel requires would necessitate some such means. In the movie, drugs are used to put the astronauts into deep sleep. Taylor administers injections to others and then himself before making the voyage.
The use of drugs to slow astronauts’ metabolisms may have been considered by NASA for actual use. As legend has it, explorer and author Wade Davis undertook research at the behest of NASA on zombification in Haiti, with the goal of finding the toxin used to simulate death so that the victim would “survive” burial. NASA supposedly wanted to test the toxin for use on astronauts in interplanetary space flight. Whichever means are used, this type of time-travel is a one-way trip. There’s no returning to the past to catch the time that is missed.
A much more space-age possibility, well known to all science fiction buffs, is suggested by relativity theory. As Einstein showed, the rate of change is relative to your frame of reference, and slows with acceleration. If you travel fast enough—at high speeds approaching the speed of light—time slows for the vehicle and everything within it. This is the method chosen by Boulle to get his adventurers to Betelgeuse. In Part 1, Chapter 2, Professor Antelle, the scientist who organizes the expedition, explains to Ulysse Mérou, the journalist who tags along, the phenomenon of time dilation—what would be two years on board the ship would be three hundred and fifty years on Earth. Mérou slyly comments that the sole inconvenience is that if one were to return one day, he would find the planet aged seven to eight hundred years. In the movie, time dilation is exploited in addition to chemical means, but it is merely suggested and not explained.
Boulle sets the stage for the finale in the penultimate chapter, where the phenomenon of time dilation becomes a plot point. When Cornelius is helping Mérou to escape from Soror via space flight to the waiting spacecraft, Mérou announces that he will return to help the humans rebel against the apes. Cornelius reminds him that due to time dilation, this would not be for a thousand years, Soror time. This argument works on the chimpanzees, who were about to prevent him from leaving, for they realize that they and other apes will no longer exist by then.
Using relativistic time dilation for forward time travel may never be possible. No one knows how to accelerate large objects to such extraordinary speeds. But conceptually, forward time travel through time dilation is no different than through chemical means or freezing. And just as with those means, there is no way to exploit relativistic time dilation for a return trip.
The Rules of Euclid, Being Completely False, Must Be on Account of That, Universal
Backward time travel can seem in some ways to be the flip side of forward time travel. Thus the plot of Escape from the Planet of the Apes is like a mirror image of the original movie—instead of civilized humans from the past traveling to an ape-dominated future, civilized apes from the future travel to a humandominated past. Yet the practical and philosophical difficulties raised by backward time travel only underscore how utterly, different it is from mere forward time travel. Let’s begin with some of the practical problems.
Almost twenty years ago, I met a physicist who worked for NASA. When I told him that I worked on the philosophy of time, he asked, “Do you know the easiest way to construct a time machine? You take a wormhole and expand it until its diameter is one astronomical unit in length.” I thought that this was very funny, on the order of the old Steve Martin joke about how you can be a millionaire and not pay taxes. “First, you get a million dollars.” (Then don’t pay taxes.)
Not much has changed in the way physicists talk about time travel—it’s still about wormholes, which are tiny black holes which, if set spinning fast enough, will in theory warp space-time to such a degree that they could connect two points which are spatio-temporally very distant. No one has found a wormhole, and there is no observable evidence that they exist, but in the last twenty years, physicists have found evidence for black holes. All suppositions about wormholes and time travel are based on mathematical equations used in theoretical physics. Perhaps it was wise for the makers of Escape from the Planet of the Apes not to try to provide a serious explanation of Zira’s and Cornelius’s trip from the future.
We should be cautious in drawing conclusions about physical reality from mathematical equations alone. The formal systems of mathematics do not always provide answers which correspond to the physical world. Consider the Pythagorean theorem. The length of the hypotenuse of a right triangle is equal to the square root of the sum of the squares of the other two sides. So the hypotenuse of a right triangle with lengths of 3 and 4 for its two sides is what? The number 5 is what always comes to mind. While this is correct, it is only one of the two possible solutions to the equation. The square of –5 is also equal to 25, and thus also solves the equation. But we automatically exclude that answer because the hypotenuse cannot have a negative length.
Our feeling that mathematics always provides correct answers depends on a mental trick: the use of non-mathematical knowledge to rule out certain solutions when solving the equations. Furthermore, the Pythagorean theorem holds only for Euclidean geometry. Euclidean geometry describes space to a very high degree of approximation; such a high degree that it was taken for centuries to be absolutely exact and the paradigm of science. But with the discovery of non-Euclidean geometries and relativity theory, we know that mathematics needs to be checked against reality.
Boulle drives this point home when Mérou is trying to establish communication with Zira. In his notebook, he draws a geometrical figure illustrating the Pythagorean theorem. Mérou then recalls having discussed with Professor Antelle the use of geometry as a means of communicating with alien beings. Antelle had approved, adding that “the rules of Euclid, being completely false, must be on account of that, universal.”
Another example of the problematic relationship between mathematics and reality can be taken from arithmetic. All numbers on a temperature scale function equally in arithmetical equations. If we consider Celsius, 200, 100, 0, –100, –200 all can be used in simple arithmetical equations to calculate temperatures. The same equations come up with answers for the numbers corresponding to –300 and –400. But these temperatures don’t exist! There are no temperatures corresponding to these numbers because they are below absolute zero—the point at which motion ceases. Just because something is mathematically possible doesn’t mean it is physically possible.
This worry becomes especially serious when it comes to time. Time is treated in theoretical physics as co-ordinated with space, as if it were a fourth spatial dimension, part of a four-dimensional space-time continuum. It shows up as a number in an equation, represented by the variable t. The possibility of going backwards in time is built into the formal system, since we can move forward or backward along the number line. Physicists tend to take the mathematics as fundamental, but it’s an open question whether time is adequately represented as a space-like dimension. This is a philosophical point, and doesn’t require sophisticated scientific or mathematical knowledge.
Can We Change the Future?
Here is where we need to think about the human experience of time. Thinking about the possibility of backward time travel is not necessarily an offbeat or peripheral area of philosophy, as it might seem if one approaches it by trying to manipulate the extremely complex equations for the gravitational warping of space-time by wormholes. The question of time travel converges with the most fundamental questions of the philosophy of time: Is time real? What is time? What is the structure of time? Is time a fundamental aspect of nature? Or an artifact of the perspective of conscious beings?
Trying to answer these questions is a complex and difficult undertaking, and philosophers have been discussing them since the very beginnings of the discipline. Today, there are three general philosophical views on time: Presentism, Possibilism, and Eternalism.
•Presentists believe that only the present moment and what is occurring now have any reality.
•Possibilists believe that the present and the past are real, but not the future.
•Eternalists believe that past, present, and future are all equally real.
These theories connect to time travel in the following way: Eternalism suggests that time travel is possible, at least metaphysically, as the past and future are metaphysically real and the present moment has no fundamental importance. Time is conceived of as a space-like dimension and we could move back and forth in time just as we can in space.
Possibilism suggests that time travel is impossible because the direction of time, from past to future, is a fundamental part of reality. No back and forth travel is possible.
Presentism, in and of itself, has no implications for time travel.
Usually the philosophy of time travel is discuss
ed not in terms of general metaphysical theories of time but in terms of paradoxes. The standard one is referred to as the “grandfather paradox.” If someone returns in time and tries to kill their grandfather when their grandfather is still a child, what will happen? If they succeed in killing him, they will not be born. If they are not born, then they will not be able to go back in time and kill their grandfather—so they will be born and will be able to go back in time to kill him.
The grandfather paradox involves trying to undo a causal sequence which has already happened. The issue raised in Escape from the Planet of the Apes is no different. When the scientific advisor to the president, Dr. Otto Hasslein, learns from Cornelius of the future take-over by apes, he wants to try to prevent this from happening—which involves killing baby Milo. Again, it’s a matter of trying to undo a causal sequence which has already happened. It doesn’t matter that the causal sequence is not in the scientist’s past, since it is in Cornelius’s past. Nor does it matter that Cornelius’s appearance will have inadvertently undone the sequence. The question is pointedly raised by the president when Hasslein explains his plan, and the president asks, “Can we change the future?”
The parallel between Escape and the “grandfather paradox” goes even further, since if there is no ape takeover then Cornelius and Zira will not be scientists, and they will not be able to travel into the past. If they are unable to travel into the past, they will not be able to provide the information about the ape takeover and the takeover will not be prevented. By focusing on the contradictory nature of the actions involved, discussions of time travel seem to allow a way out. This involves the idea of a causal loop. And this is indeed the way taken in Escape. The ape scientists’ trip to the past leads to the ape takeover—through the agency of baby Milo—which produces the ape scientists which leads to their trip to the past. A causal loop removes the contradictory aspects of the paradox. In order to permit causal influence of the past by time travel, a corollary has to be included though. Any attempt to undo the causal chain will fail. Without this corollary, trips into the past would lead to the physical impossibilities set forth in the grandfather paradox. Thus the attempt to kill little Milo in Escape fails because Zira has left him with the apes in Ricardo Montalban’s circus.
