As anyone who reads this blog with any regularity (in spite of the inexcusable irregularity of my posts..) will know, I love subjects like cosmology, physics, quantum mechanics, etc. While I do not profess to have a working knowledge of any of these subjects (I really, really suck at math–there goes my dream of being a famous quantum physicist), I have read a fair amount of literature concerning them and have spent considerable time contemplating the relationship of discoveries in cosmology and physics to the task and meaning of theology.

This post is not about that kind of contemplation.

Rather, I really just want to talk about the issues that would, in my understanding, make time-travel incredibly difficult to conceive, much less actuate. Random, huh?

The classic conundrum of speculations about time-travel has been exhausted in literature, art, film, music, etc. Probably the most famous example is the movie Back to the Future. In this movie, Marty McFly is hurtled 30 years in the past while attempting to escape from terrorists (perhaps this could be a new Bush Administration policy). While still trying to understand what has occurred, Marty accidentally interferes with the first meeting of his then-teenage parents. Made to realize the gravity of his action by "Doc" Brown, Marty struggles the rest of the film to recreate the meeting between his parents so that they might kiss, fall in love, get married and–inevitably–conceive Marty.

The dilemma of the events is clear: if Marty's parents do not kiss, fall in love, get married, etc., then how can they conceive Marty so as to actualize his existence in the future? And, of course, related is the question of how Marty could have traveled to the past in the first place to screw up his parent's meeting if, in fact, his foiling of their eventual union would result in the non-actualization of Marty's future (and therefore, past) existence; that is, if the future Marty prevented his parent's union in the past, how could the future Marty (whose existence is dependent upon non-prevention of his parent's copulation) travel to the past to prevent his own conception?

To quote the famous Powersian mantra, "I've just gone cross-eyed."

There are several classic answers to this potential paradox. The first, and seemingly most obvious, is that there exists no past in which Marty does not travel from the future. In this sense, for Marty to travel into the past to prevent his parent's union is precisely the causal mechanism by which his existence is actualized. Another would be that such an expedition into the wild world of time-travel would alter the future based on changes made in the past. This, in fact, happens in Back to the Future, as Marty returns to a similar, yet significantly altered future (a better one for him and his family, in keeping with the sentimentality of Hollywood). Simply put, any future actualized before time travel would be erased, and an entirely new one would be written, a future possessing (well, potentially at least) a resemblance of the former, yet strewn with obvious differences. A third possibility would be that of imagining a fixed gulf between past and future. In such a reality, it is speculatively possible for the future agent to travel to the past. However, this time-traveler would only be but an observer in the past without power to enact any actual change. Brian Greene suggests this as a viable option. He offers that if one were to travel to the past with the intention of killing one's father (thus preventing one's own birth), a seemingly inexplicable chain of events would transpire which would infallibly prevent one from tampering with any section of reality-past that would lead to the non-actualization of one's existence in the future. Therefore, even if one were to raise a gun, aim it, and shoot to kill one's own father, something would interfere to prevent your father's death and any other connected events that would server to actualize one's future non-existence.

While all of these suggestions are compelling on one level or another, I think most fall prey to at least two errors. The first is the obvious supposition that "past" and "future" are linearly related to one another, as if one is the "cause" of the other. The first suggestion outlined above seems to escape this objection by advocating that the time travel of Marty is essential to Marty's existence, but the other two clearly seem to view the past and future as objective points on a linearly discernible "arrow" of time. The second error is that all theories outlined above concentrate on the relationship between "past" and "future" as characterized by "events."

But is this linear, causal, and event-oriented conception of "time" helpful? Perhaps. I do not deny that powerful arguments (particularly that of common experience) can be made in its defense. However, I think that it leads to some rather serious philosophical dead-ends. First of all, regarding time-travel, I would suggest that one should be much more concerned with the stability of the universe and the integrity of one's own ontology than whether or not one's drinking of a Diet Coke in the past will significantly alter the future. As is obvious from a moment's reflection, human persons are not static objects that hurtle through time. Rather, as we live, grow and die, we are constantly changing. In any given moment, the constituent elements of our persons are being swapped back and forth across the cosmos. In this sense, our ultimate biological identity is never fixed; rather, like a swiftly moving river, we are ever changing, ever fluid.

Therefore, the question ultimately has to be raised, what would become of us if our fluid, ever-changing biological identities were to be transposed even a fraction of a second into the past, a past conceived of as a static reality?

Let me give an example. Suppose that one could freeze the universe, from the movement of the stars to the chaos of quantum fluxuations. If one were to narrow the gaze to an individual person, one would find an impossibly complex arrangement of molecules, electrons, gluons, protons, etc. which have been collected into this one frozen frame from all corners of the universe. Now suppose that we hurtle this frozen collection of the universe's DNA 50 years into the past,. What would happen?
Obviously, the answer cannot be known. However, an important issue to understand would be precisely how the conglomeration which we call a "person" would react in such an environment or, perhaps more importantly, how the environment would react to such a person. After all, in order to recreate the snapshot we have taken of the futured person, precisely every piece of constituent material which formed the snapshot would need to be compiled. But the rub is that there cannot simply be "duplicates," nor will similar elements be sufficient. Rather, every atom, every quark, every gluon that composed the snapshot person would have to be found and organized to precisely recreate the person. This means that objects, structures and realities which exist in the past which is being invaded by our snapshot person would have to give up any pieces that would be necessary to actualize the past existence of the person.

Another example… Jack is a rabid classic car enthusiast. Over the years, he has built, from a conglomeration of original classic car parts, a beautiful replica of a 1957 Chevy. Upon learning that time travel is possible (how fortunate for this example!), Jack decides that he would like to take his pride and joy to the past–1957 to be exact–in order to show it off in a new car showcase for Chevrolet which he remembers reading abou
as a kid. His mo
tivation, ultimately, is to see the cars that built his. He still has the parts' serial numbers, so he concludes the he will able to determine precisely every car whose parts went into the creation of his automobile.

So Jack hooks up his portable flux capacitor and rockets down the road until he reaches 88 mph. At that instant, something happens (a tear in the fabric of space/time, a wormhole, whatever) and he is transported to the past: he has successfully reached 1957!

However, as he soon comes to realize, no model showcase exists. After inquiring with Chevrolet's support desk, Jack learns that the show was cancelled because a large batch of the newest models had disappeared–there were no cars to display at all!

What has happened? When Jack took his Chevy to the past, all of the constituent parts that composed his Chevy had to be compiled. Therefore, any models that had Jack's car's pieces disappeared, for (in this example) 57 Chevy's do not exist without sidemirrors, clutch pedals, etc. When Jack and his car traveled to the past, Jack's car assumed ontological priority over the myriad cars of which Jack's car was composed. In short, their past existence was non-actualized to allow for the actualization of Jack's car in the past.

Now let's back up a bit. Sure, car parts are significant; they are tangible and integral to a car's operation. But what if we expand our view to the universe? What are a few gluons and protons in light of the size and immensity of the entire universe? On the surface, this may not seem to be such a big deal. After all, what are a few electrons to a red giant star, or even a few atoms to a fully grown human? However, this scale on which these elements exist is deceiving. Just because something is nearly infinitely small does not mean that it does not have profound influence on the universe as a whole. Quantum mechanics reveals that the interconnectivity of the underlying forces within the universe is so fragile that even slight changes on the farthest edge of the universe has indelible influences throughout.

So be it. But there is something even more profound that should be recognized. What has happened in Jack's adventure? The short answer is not that the past was "changed." Rather, Jack's foray into time travel has actually created its own reality. After all, if the reality of Jack's time travel actually creates a differently reality than that which was expected (i.e., the car show was only existent in the past when Jack and his car were not there), can it really be said that Jack traveled to the past?
I would argue that the answer is no. Traveling to the "past" or to the "future" is only meaningful if each exists as a static, objective reality over and against each other. However, as has been noted in the example of Jack's car, any attempt to travel in time would be unsuccessful. One's very presence would assume ontological and causal priority, effectively shaping the past, present and future to be exactly in keeping with one's ontology. Jack's example, ultimately, is inadequate on this level, for Jack–in traveling to 1957–would have no knowledge of the car show ever existing. By existing in 1957 with his 57 Chevy, the past to which Jack attempted to go never existed. Therefore, as the categories of "past" "present" and "future" are entirely based upon the ontological status of the one experiencing them, any potential forays into time travel would be undetectable. Because the passage of time will always conform to the ontological status of the observer, one could be jumping through multiple stasis of space/time innumerable times in a given moment and never even realize it. After arriving at his destination, Jack would know of nothing amiss. He would not realize that he was "in" 1957 as opposed to 2007, nor would it seem odd to him that he was there. In this way, travel through time would look exactly as it one would expect it to look, expectations based not upon the imaginations of writers, film producers, or video game makers, but rather expectations based upon the brute force which tensed ontology wields over human existence.