Philosophy of Time Travel

Transcription

1 Philosophy of Time Travel Rob McCarthy For as long as can be remembered, the human imagination has been enamored of the possibility of traveling back in time. We all fantasize about what it would be like if we could go back in time and change a bad decision, or event that had a negative effect. Science fiction has fed off of this fascination and produced many fantasies about individuals who invented a time machine that had the power to transport them to the past or the future and view or change the course of time. But what about the contradictions that can come about if time travel were possible? Could you go back in time and kill your grandfather and remove the means for your existence, therefore removing the possibility of going back in time and killing your grandfather? This paper will address the aspects of time travel and why it is logically impossible. To grasp some understanding of time travel, we must first understand something about the nature of time. The obvious answer to the question, What is time? goes something like: Time is what a clock measures. But, like the centimeter measures distance, isn t a second just a contrivance of human beings to describe a relationship? What about the question of time only existing in the human mind? Would the past even exist if there is nothing that remembers it? There are three differing theories on the nature of time; these are Presentism, the Growing Universe Theory, and Eternalism. Presentism states that only objects and experiences in the present are real, and that the past only exists in memory. The growing universe theory states that the past and the present are real but the future is not. Finally, Eternalism states that the past, present and future have no differences because they are all subjective.

2 Although there are many different views on the nature of time, they each deserve a paper of their own just to be accurately described. To avoid a drawn out description, I will attempt to offer a definition of my own: Since time is a relationship between temporal events, time could be described as the field in which a cause precedes an effect. Additionally, this field allows motion in one direction; the cause always precedes effect. Just as it is easiest to imagine space-time having a Euclidean geometry, it is easiest to imagine time as being a line that travels in one direction. Although it has been suggested that perhaps time has a circular geometry, repeating a cycle over and over, the common conception of time is as having a linear geometry. According to Adolf Grünbaum, time is described as mathematically continuous, traveling in one direction with no breaks or jumps. The advent of Einstien s theory of relativity changed much of philosophy s views on time. It was commonly accepted that time was linear and could not be curved or circular, however Gödel discovered that Einstien s equations allowed for the existence of casual loops in time. ( A causal loop can be described as a loop in time, in which a series of causes and effects loop back upon each other. For example, A causes B, B causes C, C causes D which causes A. The Internet Encyclopedia of Philosophy s essay on time travel provides a good example of a causal loop:

3 ( The problem with the idea of causal loops lies in the fact that they are infinite cycles in which they are a sequence of causes and effects started by an event which was introduced ex nihilo. However, some events occur that apparently have no cause, such as the big bang. This leads one to wonder if time itself is entirely one large causal loop, with the big bang as the beginning and eventual end, and therefore time is entirely circular in geometry rather than linear. ( So, if according to the theory of relativity causal loops are possible, can that imply a paradox? Logically a cause always has to precede an effect. It would be illogical to say, My car ran out of gas because I walked home. So if a causal loop is possible, what if it allowed for a cause to produce an effect which in turn causes the original cause not to produce its effect? In other words, what if A causes B, and B causes C which in turn causes A to not cause B? This is aptly referred to as the Grandfather Paradox, Which is described in The Stanford Library of Philosophy as follows: A man builds a time machine He goes back in time and kills his grandfather His grandfather can t have children The man end s his own existence He can t go back and kill his grandfather (

4 So if time travel is possible, would that entail that one could only travel back in time as long as he doesn t commit the grandfather paradox? Perhaps the man could travel back in time with the intent of killing his grandfather but events conspire against him, so that in every case he fails, and the progression of events is not disturbed. If the man is destined to fail doesn t he have constraining conditions set on him that inhibit his free will to kill his grandfather? The philosophy of time travel, as well as philosophy of free will, have many implications on the grandfather paradox. ( Let s say that the man can travel backwards in time. But if he tries to commit the grandfather paradox, he is destined to fail. Could the man still say that he can act of his own free will or is a deterministic progression of events forcing him into a certain outcome? My conclusion is that time travel cannot exist without a deterministic progression of time. However, if one were to travel back in time, the simple act of existing in a time frame, where they did not exist before, will alter the course of that deterministic progression of time, which is impossible. That person could not step on an ant, for example without significantly altering a chain of causality. All in all, the idea of time travel is entertaining material for science fiction books, but in reality is highly improbable if not impossible.

5 References: Artzenius, Frank and Maudlin, Tim. Time Travel and Modern Physics. Stanford Encyclopedia of Philosophy < Dowden, Bradley. Time. The Internet Encyclopedia of Philosophy California State University < Hunter, Joel. Time Travel. The Internet Encyclopedia of Philosophy University of Kentucky <