Time travel has been featured in many stories of fiction, sometimes to the intense puzzlement and confusion of readers, moviegoers, and gamers! Today, I start a mini-series on what distinguishes logically possible scenarios of time travel from scenarios that are objectively impossible. Although I suspect that many readers of mine already know what time travel is, I will define my terms anyway. Time travel is the process of migrating from one point in time to another that is not the usual method of moving through time--living in the present as future moments become the present and fade into the past.
The past, of course, refers to moments and durations of time that have already elapsed; the present, to the current moment of time that is just about to become part of the past; the future, to moments and durations of time that have not yet elapsed. Time travel is often utilized in stories in ways which render the stories incoherent and self-contradictory. To demonstrate what it means for time travel to form a contradiction, I will address the infamous grandfather paradox before inspecting an example of logically-impossible time travel from a popular movie. In the sequel to this post, I will explain an example of time travel that does not create a contradiction. Now, onward to the grandfather paradox!
The grandfather paradox refers to a hypothetical scenario where someone travels back in time and kills his or her grandfather. Let's say that Amanda travels backward in time and kills her paternal grandpa before he helped produce her father. This would mean that since her father no longer exists, she can no longer exist as well. Thus Amanda could not have traveled back in time to kill her grandpa. Though it is called a paradox, it really becomes a contradiction. Amanda cannot perform the action she went back in time to enact without nullifying the very biological basis for her existence, preventing her from being able to travel back in time because she does not exist. The deductive reasoning here is simple. A variation of this would be me going back in time to kill myself as a baby or young child, ending my existence because I could never have existed in the present to go back in time to kill myself.
Now, for a time travel contradiction that is utterly impossible, I will reference one of my favorite movies. In James Cameron's film The Terminator, soldier Kyle Reese is sent from the year 2029 to 1984 to protect Sarah Connor, whose son John will lead a human resistance against a faction of robots called Skynet. As he guards Sarah, the two eventually become romantically involved and have sex, with Kyle impregnating Sarah. She gives birth to John Connor, who goes on to fight Skynet and send Kyle back in time to protect his mother. The contradiction lies in the fact that had John Connor not already existed in the future to send Kyle Reese into the past, Kyle would never have existed alongside Sarah, meaning she would not have become pregnant and given birth to John. Since in this instance what happened in the year 1984 could not have occurred without something having already happened in the future year of 2029, and since the past must by necessity occur before the future, the time traveling scenario in The Terminator is logically impossible. This scenario is not a paradox, where something seems to be a contradiction but on a closer examination is actually possible or true; it is an impossible contradiction. It could never happen.
While the time travel plot in The Terminator is inescapably impossible, in the next post in this series I will examine an instance of time travel from the future to the past in a popular video game that does not violate logic. At that point I will elaborate on what makes the time travel from the video game in question possible as opposed to the incoherent nonsense from The Terminator. Yes, I love The Terminator and I love its immediate sequel even more, but the contradiction at the heart of its premise does not vanish because of my appreciation for the movie. But not all time travel is logically impossible!
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