The subject of time travel is one that mankind has been fascinated with since before the concept was even fully developed. The idea that we can change events in the past in order to consciously sculpt the future is something that almost everybody has thought about on some level. While both artists and philosophers have discussed the topic of time travel, there remains some controversy regarding its theoretical possibility. Some argue that because of certain paradoxical events which could occur, it impossible to travel through time. Time travel is theoretically possible due to the ideas of personal and external time, even though it may not seem so from a standard view of time.
As a literary device time travel is most often used to convey the theme of fate, or predestination, as triumphant over free will. Much like the idea of self-fulfilling prophecy, predestination paradoxes are often used to exemplify a character's lack of free will. When this is the case, the character will know of an event either through lived experience in the case of time travel, or through prophecy, and they attempt to change what they know of the causes of that event. With time travel, the method of changing the present or future events is to eliminate their causes in the past. With prophecy in literature, however, the process is a little more complicated; because the event has not occurred yet, the causes may still be unknown. Therefore, in deterministic literature it is most often the character's attempted negation of the prophecy which causes the event to unfold.
Perhaps the most well-known victim of self-fulfilling prophecy is the tragic hero Oedipus. Before Oedipus's birth, his father, Laius, the King of Thebes, consulted the oracle to ask what kind of children he would have. The oracle prophesied that any son of Lauis would grow up to murder his father and marry his mother. Of course, Laius tried to keep the prophecy from being fulfilled by giving his son to a servant to abandon, but the servant ends up giving Oedipus to a poor family who raised him outside of Thebes. Years later, when Oedipus is a grown man, he met his father as a stranger traveling on the same road. They argued with each other until eventually a fight broke out, which led to Oedipus fulfilling the first part of the prophecy: the murder of his father. Oedipus later saved Thebes from a sphinx, causing him to inherit the title of King of Thebes, as well as his mother, the recently widowed Queen. This is a basic example of a predestination paradox because the events which caused the prophecy to be fulfilled were all linked to the conscious efforts of Laius to avoid the prophecy.
Much like prophecy, time travel can also be used to incorporate the the theme of fate in literature. Predestination paradoxes within time traveling scenarios start with a character who wants to change their present situation by altering the events of the past. In traveling to the past to undo the causes of the present, they either become the cause themselves, or become the cause of the original cause: setting in motion the same cycle they tried to prevent. The most famous hypothetical example of this would be any time traveling situation in which the traveler becomes his own grandfather, paradoxically causing their own existence years before they are even born. Of course, this is only possible in the first place due to the theoretical difference between personal and external time.
Traditionally, we view time as a universal force which moves forward at the same rate for everyone and everything, regardless of where they are in the universe. When examining the concept of time travel, however, more complex models of time are sometimes necessary. For instance, when traveling 20 years into the past, time is reversed by 20 years for everything except the traveler. This is because he has moved through external time, but his own personal time continues to progress as normal. If it were otherwise, the traveler would find himself 20 years younger, doing whatever they were doing then. A traveler would also be unable to travel to any time before their birth, or after their death, because with only external time, he cannot unhinge himself from his constantly looping time-line. Instead, the ideas of personal and external time, as proposed by David Lewis, ensure a way of differentiating between the traveler's personal experience of time, and time as the rest of the world perceives it.
Personal and external time are generally one and the same for everyone who is not a time traveler, but for the traveler, some interesting questions may arise as a result of disjointing their personal time from external time. For instance, it is possible that the time from which the traveler departed could still be progressing at what we consider to be the regular rate. In these scenarios, a traveler who has spent five years in another time may attempt to return to the present only to find himself 5 years later from his starting point. Of course, all the traveler would have to do is go back five years from that point to reach their date of departure, but by doing so, they would essentially always be living five years in the past, as the present he left would continue to exist ahead of him.
Regardless of whether or not time continues progress from the point of a time traveler's departure, personal and universal time will always be at least slightly disjointed upon the traveler's return. This is another distinction which would be impossible to understand without the notion of personal time. A traveler who has lived even a single moment in either the past or the future will have gained experiences which are chronologically different from the flow of external time. Because of this distinction, a traveler will still age regularly in the past and future, and can actually die before the time of their birth. By the same principles, an object made today and left a thousand years in the past could be dated as a thousand years old, even though it was manufactured on the same day it was dated.
The notions of personal and external time can become even more confusing when one considers fiction such as Jorge Luis Borges's “The Other,” in which a character converses with himself through an act of time travel. In this story, Borges as an old man sits on a park bench, where he is joined by a younger version of himself. This story does not give any account of how the time traveling is managed, but the entire thing is described as if it were a scenario of deja vu, and Borge even writes that it was a very dreamlike encounter. Lewis would say the reason for the deja vu quality of this kind of experience is because the event takes place twice in the traveler's, in this case Borges's. personal time, but only once in external time. The reason for this, is that Borges actually experiences the event twice: once as a younger man, and once as an older, and has different thoughts and reactions to it each time. Even though the traveler experiences it twice, this is still a single event in external time, because any outside observer would view it as such.
These concepts dissolve one of the more basic paradoxes of time travel, as well: that it is impossible to travel any period of time without that period of time passing. This paradox would reduce the entire notion of time travel to just waiting for the desired time period to occur, if it were not for the concepts of personal and external time. For a traveler, the trip from the present to any other point in time is measured in personal time, as external time would flow quite differently outside the time machine. In this sense, traveling a thousand years in either direction could take only a moment of the traveler's personal time. As I briefly mentioned earlier, without personal and external time, a traveler could not go to any time before his birth or after his death. This is because with only external time, they would find themselves as the same person they were at that time, performing the same actions, defeating the entire purpose of time travel. With personal time, however, the traveler is a different person from his other self because he has different experiences.
One of the most intriguing paradoxes of time travel, as stated by Paul Horwich, is that “Whatever has already happened cannot now be undone.” (Horwich 435). This is another paradox that makes time travel completely irrelevant, as it states that nothing can be changed because it has already happened. Horwich argues that it is, in fact, logically impossible to change the events of the past, but not to influence them in the same way that we always influence future events. Of course, this still allows for a present in which events have been influenced in the past by people from the future, or a predestination paradox. In this situation, the causes and events would not be fully understood until external time caught up with the personal time of the traveler's departure. This is just one of several techniques used in literature to avoid this particular paradox of time travel.
Another way of avoiding the paradox that the past cannot be changed is to say that the time traveler has moved not only through time, but through universes to an alternate reality. This concept is not really a solution to the paradox at all, but merely a neat hypothetical sidestepping of it. In this theory, the traveler could change all he wanted without becoming the victim of paradox, because the events which he changes are not truly the events he remembers, just different version of very similar, possibly identical, situations. DC comics has long been criticized for using this technique to bring back dead characters. Sometimes Superman must fight alternate versions of himself, or is even saved by himself. This concept has become more popular recently as the genre of alternate history is becoming more prevalent, but alternate history should not be confused with time travel, though they are similar situations.
Alternate history stories are different from time traveling stories because rather than having an agent, or time traveler, change the past, they are hypothetical situations in which a past event occurred differently, making the time-line different from the one we know. To draw on another graphic novel reference, Alan Moore's Watchmen is an alternate history story in which the pivotal change from our own time-line is the existence of masked vigilantes in the 40s through the 60s. In the Watchmen universe, the vigilantes lead to America “winning” the Vietnam War, which causes Richard Nixon to serve five terms as president. A recent novel, And Then Everything Changed, by Jeff Greenfield, contains alternate histories for President Kennedy and his brother, Robert, as well as for Presidents Carter, Ford, and Reagan. Any one of these situations could be explained by time travel, but are instead just hypothetical alternate universes.
Another of the most commonly discussed issues of time travel are the creation of causal loops within time. According to Lewis, a closed loop is scenario in which “each event on the loop has a causal explanation, being caused by events elsewhere on the loop,” (Lewis 148) In other words, there is no way to determine what the original cause was, because each one loops back on the other an infinite number of times. This typically leads to a predestination paradox, as described earlier. Now that we have a greater understanding of the workings of personal and external time, let's look again at the infamous grandfather paradox, with a strange twist, as told by Matt Groening's animated series Futurama.
In the Futurama episode “Roswell That Ends Well,” Fry causes the crews' spaceship to be transported back to Roswell, New Mexico in 1947, ultimately becoming the “Area 51” aliens, which influenced a lot of Fry's beliefs and interests. Furthermore, Fry ends up accidentally killing his grandfather, and sleeping with his grandmother, paradoxically becoming his own grandfather. This situation is a causal loop, because it is impossible to determine which events determined the others. Specifically, where did Fry come from in the first place? Fry's personal time, that is the way he experienced time, is easily traced. His existence in terms of external time, however are difficult to understand.
As Fry experienced his life, he was born, grew up, went back in time, killed his grandfather, slept with his grandmother, then went back to the present and continued to live. In terms of external time, however, Fry murdered his grandfather, slept with his grandmother, and disappeared. Then, decades later, Fry was born, he grew, up, disappeared, then reappeared a short time later. In this case, Fry is able to go on living his life after the whole incident, but suppose a traveler in a similar position never makes it back to their starting point and dies in the past. The causal loop would be closed, and the events which caused the time travel would repeat themselves infinitely from Fry's point of view. A view of external time, however, would proceed as it was before, but Fry would simply not reappear a short time later. Such a difference between infinite repetition, and time progressing naturally with a minor bump suggest that even if paradoxes such as the proposed situation do occur, they are just minor eddies in the flow of time as we all experience it.
Turning again to Borges's “The Other,” we see another example of as circular loop. Though the conversation happens in a single moment in external time, the fact that it was between the same man at different times in his life creates the loop. The old Borges vaguely remembers the conversation he had with himself as a young man, and remembers that he must pass on good advice to himself to shape the man he will become. So he essentially grows up to be the old Borges based on the information he gives to his younger self. In this case, where does the original information come from? As Lewis says when examining a similar situation, “There simply is no answer. The parts of the loop are explicable, the whole of it is not. Strange! But not impossible,” (Lewis 148). It is indeed strange, but as demonstrated, this is paradoxical only from a view of personal time, and does not automatically negate the possibility of time travel.
Though the majority of stories involving time travel involve causal loops, this does not at all mean that time travel is impossible. In fact, there are certainly more possible situations that do not lead to causal loops than do. As Bradley Monton says in an article on the possibilities of time travel, “I know of no extant consistent time travel story which does not involve causal loops, and it may well be the case that such a story would not be interesting. But it does not follow that such a story is not possible,” (Monton 3).
While time travel has been both a literary focus and a point of philosophical debate, it seems to have very little use except in the hands of a highly trained professional who wishes only to observe. If there is one thing we know about time travel, it's that the consequences of making a mistake in the past can be so disastrous, that it's literally beyond comprehending. The philosophical consequences for the individuals involved in time traveling definitely outweigh the benefits of changing the past. Perhaps the best way to avoid these devastating consequences is to not attempt to change history through time travel, but use it to learn history we do not already understand, much like Mister Peabody and Sherman.
Works Cited
Borges, Jorge Luis. “The Other.” Collected Fictions of Jorge Luis Borges. Penguin Books, New York, New York. 1998. Pages 411-418. Print.
Horwich, Paul. “On Some Alleged Paradoxes of Time Travel.” The Journal of Philosophy, 72.14 (1975). Pages 432-444. Retrieved May 6, 2011 from JSTOR.
Lewis, David. “The Paradoxes of Time Travel.” American Philosophical Quarterly, April 1976. Pages 145-152. Retrieved May 4, 2011 from JSTOR.
Monton, Bradley. “Time Travel Without Causal Loops.” American Philosophical Quarterly, Journal Compilation, 2008. Pages 1-14. Retrieved May 9, 2011 from JSTOR.
“Roswell That Ends Well.” Futurama. Matt Groening, Rich Moore, Billy West, Katey Sagal. Comedy Central, 2001.
