Time travel: is it the future or is it fantasy?

by Ben Brown

Because of the great advances that science has made in recent centuries many people have come to think there is nothing it can’t do. Time after time, what had been thought impossible or unknowable has been accomplished or discovered by science: speeds faster than sound, the nature and behavior of the few fundamental building blocks of matter, men on the moon, etc.

We have naturally become hesitant to say that anything currently unattainable is absolutely so. After all, millions of people once thought that it was impossible for men to travel into outer space. Some seem to think this way even about time travel. “It’s impossible now, but who knows what science will accomplish in 30 years?”

I would like to offer a few arguments here as to why I think that it is just plain impossible for anyone or anything to travel either back or forward in time.

I begin by noting the distinction between that which is conditionally impossible and that which is absolutely impossible. Something that is conditionally impossible is impossible by virtue of circumstances, whereas an absolute impossibility is so in itself, regardless of circumstances. For instance, it is impossible for me to kick down my apartment door. I am not strong enough. My lack of strength is a non-necessary circumstance, which theoretically could change, making it possible for me to do what I can’t do today. It is also impossible for me to be strong enough to kick down the door and at the same time not strong enough to do so. But that is an absolute impossibility. No imaginable change in circumstances could remove such an impossibility.

My position is that there is something absolutely impossible about time travel.

Most of my work in demonstrating this has actually already been accomplished for me. We have all probably seen a movie or TV show in which the famous chicken-or-the-egg time “paradox’ is explained or depicted. A person does thing X1 at time T1, which has as its direct result that he travels back in time and does thing X2 in time T2; but it turns out that X2 was actually the direct cause of his doing X1, and thus he would never have traveled to time T2 and done X2. In other words, X1 requires X2 to happen first temporally, but X2 requires X1 to happen first temporally. Now, a person cannot brush his teeth before combing his hair and also comb his hair before brushing his teeth. To say that one both brushed first and combed first is a contradiction, because both cannot simultaneously be true. The same holds for X1 and X2. X1 must happen before X2 (or it could not be the cause of X2) and X2 must happen before X1 (or it could not be the cause of X1), and so to posit that time travel is possible is to posit that a direct contradiction is possible, which is impossible.

Some people like to call this a paradox, but I find nothing paradoxical in it. It is simply an outright impossibility, a direct contradiction. It is only a paradox if you actually assume that time travel is possible. But if you use simple reason, the solution is simple: if assuming something to be true leads to a logical contradiction, then your assumption must be false. There is no other alternative.

A second argument goes as follows: To consider time travel possible is to consider time as a sort of continuum, like a line that goes on in both directions, each point “simultaneously” existing. We normally travel through time, along the line, at some certain rate, time travelers suppose. But as we leave one instant and enter the next (as if there are actual individual instants), the last instant does not cease to exist. Rather we (or our past selves) are still reliving it over and over again, unceasingly. If this were not the case, then what would there be to travel back to? I can therefore travel back and meet my past self. On the one hand, he is obviously not me despite the fact that we have the same DNA.

But on the other hand if my “past self” isn’t me, the real, honest-to-goodness, material and spiritual, unrepeatable, incommunicable me, then it’s not really and truly my life that he’s living, but rather his own, and it’s not really me who decided to do such and such past action. This, of course, is ridiculous. Even more ridiculous are some of the consequences that seem to follow from it, such as the result that no one can really be held morally responsible for their past action, since not they, but their past selves performed those actions.

Consider also that such a theory of time travel would imply that there are a really real infinite number of human persons, all simultaneously existing as we speak. And even more so, there are an infinite number who come into existence during the course of any given millisecond. From a Christian perspective, this is, of course, untenable. Only God can be really infinite. We might also note that thinking along these lines has led seemingly intelligent scientists to actually propose and maintain that there are, or very well may be, an infinite number of universes, each spawned by a different self making a different choice at some moment in his life.

Consider a fourth problem. If one goes back in time and changes something, which in turn changes oneself in some way—even causes his death (in the future, but before he went to the past), then what happens to him? Does he instantly change? If so, I cannot even begin to imagine the mess of consequences and even contradictions that would result. (Think about it sometime, or watch any number of time travel movies or TV shows. Some episodes of Star Trek come to mind.) But if not, then it is possible for a person to not be a product of his own past; that is, one could exist without ever having been born. Once again we are led to a contradiction.

Fifthly, consider the nature of time itself. Time, Aristotle explains, is like length. It is the measurement of something else. Length is the measure of distance; time is the measure of change. No distance, no length; no change, no time. (Think about God. We say that He is “outside” time. Why? Precisely because He is immutable, unchanging. Think about what it means to be “frozen in time.” You almost certainly picture everything unmoving, unchanging, completely frozen—like a snapshot.) If you grant this, then you must be able to see that there is no such thing as “going back in time.’ To do so would be to change yourself (in at least some way), which is nothing other than to progress in time in the normal fashion. All that could be done would be to rearrange the universe such that every atom is in the same position that it was in at some point in the past. But such a rearrangement would be a change, a “movement” forward in time (not to mention the fact that the universe is more than simply matter, but includes human souls who cannot simply be rearranged like matter.) Therefore, to go back in time is impossible in the sense in which we usually mean it.

Similarly, we can see that time travel logic itself leads to the conclusion that time cannot be simply the “line” that it is assumed to be. If a person travels back in time and cuts his past self on the arm, does he suddenly acquire a scar? I think that everyone would say no (if one answers yes, then this argument does not work, though I am sure that another whole system of contradictions arises). If one travels to a point in the future after one’s death, is he himself going to die upon arriving there? Again, almost everyone would say no. Based on these two pieces of data, it seems that the time traveler is in a sense “outside time.” In his travels he is indifferent to the events of the normal timeline. And yet, he still grows old, he still maintains his memories from one time to the next, etc. In other words, he still experiences the passage of time in himself in the normal way. The conclusion is that time is change, or the measure of change (depending on the various usages.) This leads to a contradiction, namely that time travel implies two different conceptions of time, one of which excludes the other (as argued in the above paragraph).

Lastly, let me advance a simple, clear, and logical argument that should put an end to the matter once and for all. Presumably, when one says that time travel is possible one means that a person can go back, for example, to the real, true, genuine 1776. But if you’ve traveled back to the real 1776, then what are you doing there? You didn’t exist in 1776, so to say that you are in the real 1776 is to say that it’s not the real 1776, which is yet another contradiction.

Consider finally what ramifications time travel has for morality, heaven and hell, God, angels, etc. and I think that you will arrive at the same conclusion I do: to posit time travel as possible is not good science fiction, but rather unreasonable and illogical nonsense. I ended an earlier Concourse article (on evolution) with a quote from the movie “Angels in the Outfield,” which also seems particularly appropriate here. With modern science the motto seems to be that given enough time “It could happen.” But we need to use a little logic and realize that not just anything can happen.

Ben Brown, a contributing editor of the Concourse, graduated from FUS in 2000. He recently married Cindy (Ray, 2000.) They are living in Washington DC, pursuing PhDs in theology and philosophy, respectively, at Catholic University.