The following is a paper I turned in for Metaphysics.
The title: “Hitler’s Mustache, And Other Problems That Upon Solving Will Do Nothing To Benefit Humanity Whatsoever”.
Yes, I handed it in with that title.
I got 95%. If you haven’t read Lewis’ paper, you don’t need to. I make everything pretty clear, as clear as time travel can be, I reckon.
In his paper, “The Paradoxes of Time Travel”, Lewis puts forward a proposition about the nature of personal and external time. Under his proposal, one could truthfully say of a time traveler who aspired to be a barber – “Even now, long ago, he is trimming the moustache of Hitler.” First, I will outline Lewis’ argument in more detail. I will then argue that Lewis is right in this statement and that claims of that nature can be truthfully made. Lastly, I will consider some complications and counter-arguments. Once I have finished, I will take a long shower and try to forget about the entire thing.
In his paper, Lewis distinguishes the difference between personal and external time. First, he importantly outlines his belief (which I will hold as a truth in order to progress) that time is linear, a single line and not a plane. External time is time as you or I know it – the passing of seconds, minutes, decades, millenniums. External time is divided by these measures and separates one distinct event from another. For example, ten years ago I was 11 years old, seconds ago you began reading that last sentence, and so forth. Personal time is a very different notion. Lewis addresses the issue of “personal time” this way: “instead of an operational definition, we need a functional definition of personal time: it is that which occupies a certain role in the pattern of events that comprise the time traveler’s life.”
Lewis admits that this is not really time – that the passing of various events in a familiar order (first infantile, than senile stages – hair grows, food digests, memories accumulate) do not constitute themselves “time”, but something close enough to it that we can “transplant our temporal vocabulary” to it. Each change that one experiences, however small, marks a new stage of their existence. This changing of stages constitutes personal “time”.
For example, imagine I transport a blooming flower through time. Regardless of where in time that flower is sent, it will go through the stages of seedling, sprout, stem, leaves, flower bud, and blooming. For the flower, personal time marches on independent of where in history that flower has found itself, whether on the mantle of the Marx brothers or in the window of King Solomon. It will continue to grow through these stages regardless of where in time I send it (assuming where I send it is sunny and not an environment conducive to plant growth, an obvious but unnecessary complication). This growth constitutes the continual transfer through stages of the plant that Lewis would call personal time.
Lewis goes further to suggest that we can assign locations in personal time to not only a potential time traveler’s stages, but the events that occur around the time traveler during that stage. For example, I could truthfully say when referring to the personal time of a time traveler that left three hours ago to meet with Hitler and groom his infamous moustache (the rumored source of all his evil) – “Even now, long ago, he may be trimming the moustache of Hitler himself!”
Here, I agree with Lewis. It is true that a “three-hours later” stage of the time traveler is in fact in the past tending to Hitler’s appearance. Assuming that his personal time and my own were once perfectly aligned in the present, I could give the traveler an invincible wristwatch (assume such a thing exists and is incapable of error) and wear a matching wristwatch on my own arm. Setting both wristwatches for three hours, the traveler departs. Three hours from now, my wristwatch will sound its alarm. Three hours in the personal time of the traveler, the watch will sound its alarm as well. The difference is merely our locations in external time.
To provide another, perhaps stronger example is to consider if the time traveler had eaten a slice of orange prior to his trip. After three hours of being in the past, it seems to follow that the orange within the time traveler would be three hours “more digested” than when the traveler left. In this, the stage of him that exists in the past is continuous from the one he left in the present. Three hours of time have passed for him despite the fact that decades have also passed in external time. Only in referring to his personal time am I correct in making the statement, “even now, long ago, he may be trimming the moustache of Hitler himself!”. With regards to external time, I am obviously in error. I cannot truthfully say that at the very moment I am speaking three hours later, Hitler is in fact having his moustache groomed.
Here is the paradox – the event is both happening now, for the time traveler, years ago – and not happening now, for me, in the present. When I make the claim that my time traveling friend might now be trimming Hitler’s moustache, it is important that I include the short phrase “Long ago”. Without it, my statement is false. Instead I must assert that at this moment, during another separate moment in history, an event is occurring. It is only in our personal times that these moments align for the time traveler and I. Because man clearly goes through “stages” as described by Lewis, I am inclined to agree with his position on personal time and truthful statements made in its regard.
However, there some admittedly peculiar and difficult complications when accepting Lewis’ personal time concept. For example, consider that instead of one time traveler, I had commissioned six to go and report on Hitler. Three hours ago, each climbed into their own time machine and traveled to a different stage of Hitler’s life. By virtue of what I have claimed to accept, I must now make some very bizarre statements. I can say (assuming three hours has passed), “Even now, long ago, Hitler is being born, making out with Eva Braun, giving the order to invade Poland, having his moustache trimmed, taking his first steps and giving a speech.” How can it possibly be true that all of these events are occurring, “even now”? At first consideration, it seems as though this statement turns a timeline on its head. It infers that all of history and the future are occurring in this moment, one single, cosmic “yelp”. Since Lewis has argued for a linear time format, this complication at first seems to challenge his proposed structure of time.
In response to this, I must emphasize that when making his original statement, Lewis referred only to personal time, not external time. For each of my six time travelers, they experience one of these varied events at three hours later in their personal time. In external time these events remain distinct and separate, divided by months and years. In personal time, however, each of my six travelers is experiencing these moments exactly three hours after setting out. This three hours has passed the same for I as it has for them, for at once all of our personal times were aligned. Consider the problem in the sense of geographic travel. I can send six men in six cars in six different directions over the course of three hours. I can say truthfully at the end of those three hours that each man is in a different place, and nothing about this seems contradictory. In my example, each traveler has simply traveled to a different “stage” or “place” in time, and this travel in and of itself does nothing to align the events in external time. What has been aligned is the moment at which these events are being experienced by the travelers, but not their actual occurrence. This begs the original paradox. These events are occurring “even now”, but also not occurring “now”. As stated earlier – the statement is only true if making reference to personal time, but blatantly false if referring to external time. I can find no support for an argument that both events can occur simultaneously in a linear time structure.
One might also take issue with the suggestion that “personal time” can stick to one like toilet paper on the high heel of an oblivious woman leaving the bathroom. That is to say, one may posit that the notion of “taking time with you” is flawed – that personal time is simply a product of external time and that the two are inseparable. They may imagine a world without external time and argue that in that world personal time would be incapable of passing. Thus, the personal time experienced three years in the past by a time traveler and three years presently by myself are not the same. I find this position difficult to argue in favor of. A supporter of this view would need to supply reason to believe that the stages of development one goes through are somehow disjointed or separated by the act of time travel into two distinct and incomparable entities. I would refer back to the argument made for the plant – independent of where in time it travels, there are necessary stages of its lifecycle it must go through in order. The same principles apply to a time traveler, and I cannot imagine any event that would be sufficient to create a disjuncture or “new” entity separate of its past. Perhaps I just lack imagination.
Other arguments against Lewis would need to challenge his perception of time as linear. I will not address these here. Given the rigid boundaries Lewis has created his world in the context of his writing, it is difficult to disagree with the statement that within these parameters, his assertions with regards to personal time hold true.
In conclusion, I have briefly outlined Lewis arguments regarding personal time and argued that given this outline statements such as “even now, long ago, he may be trimming the moustache of Hitler himself” can be true. I have stated that these statements are only true when referring to personal time, and not to external time. I have considered some potential objections to Lewis within the context he has created of linear time, and maintained that I do not feel they are valid enough to undermine Lewis arguments.