Time travel is the concept of being ableto travel in between certain points in time, whether it be to the past or thefuture. In many movies and books, people often travel though time machines inwhich they can take the form of doors, vehicles, portals, and so on. An exampleof time travel would be where one steps into a time machine and arrives at adestination 30 years before or after the initial timeline.
It would not be consideredtime travel if someone were to turn his clock back two hours: the person didnot physically go back two hours of that day. He simply changed the time of theclock. It is unknown if time travel is possible but as of now, it is highlydoubtful.According to American philosopher DavidLewis’s article, “The Paradoxes of Time Travel”, time travel involves “adiscrepancy between time and time” (Lewis, 1). To elaborate, if an Irvinestudent were to get in his car and drive to Los Angeles, the time it takes fromthe starting point to the destination would equal the time of the journey.
However, for a time traveler, the separation in time between leaving andarriving would not be the same as the period of his journey. For example, anhour spent in the time machine does not mean the traveler is an hour ahead ofthe present: it could be days or months into the future. The Grandfather Paradox is a contradictionof time travel in which an inconsistency occurs in trying to change the past. Themain problem of it is this: A time traveler goes back in time to change thepast but it is impossible to alter it, and since the past is unchangeable, timetravel must be impossible as well. According to the lecture, the Grandfather Paradoxoccurs whenever a time traveler goes back in time and “prevents an event thatis a pre-condition of the traveler making the backward time-journey in thefirst place” (Bernecker, Grandfather Paradox, slide 1). Take, for example, thescenario used in lecture: (Premise 1) A time traveler goes to the past to killhis grandfather. (Premise 2) However, if he kills his grandfather, he cannotexist because then his mother or father, who is a child of the “murdered”grandfather, was not born.
Therefore, the time traveler does not exist and isunable to go to the past to kill his grandfather. The Grandfather Paradoxquestions whether or not we can travel to the past and change it. The mainworry of the paradox is that it would be impossible to kill the grandfathersince it violates the law of non-contradiction: the grandfather somehow bothsurvives to have kids and cease to exist. The time traveler cannot reallychange the past since his grandfather exists in the present, hence the timetraveler’s current existence. Premises 1 and 2 contradict each other so it mustmean that backwards time travel is not possible. Technically, the time travelercan murder his grandfather since heis currently living but because it would get rid of one of his parents andhimself, he can’t travel to the past. Despite the name, the Grandfather Paradoxdoes not specifically have to involve the contradiction in murdering one’sgrandfather to prevent one’s own birth. The paradox can involve anything thatalters the past, since there is an inconsistency whenever the past changes fromthe way it was.
Take another example of the paradox: A scientistgoes back in time to destroy his laboratory to prevent himself from building atime machine. He succeeds in destroying the lab but what about his invention ofthe machine? The past version of the scientist would not be able to build thetime machine that would allow him to go back to destroy the lab. The scientisthas no method of travelling to the past and thus, time travel would beimpossible.
Lewis was known for his thoughts onthe possibility of time travel and mostly, for his solution to the GrandfatherParadox. He mentions the paradox in “The Paradoxes of Time Travel” and thesolution he provides to it is one that shows that the “paradox” is not really aparadox. Lewis says we must assume the time traveler cannot change the pasteven though he can take part in it. The freedom of the time traveler must belimited since the past is fixed.
He also says there must be strangecoincidences that prevent the past from changing. For the grandfather scenario,the time traveler would not be able to murder his grandfather due to thejamming of his gun, shooting someone else, being stopped by a bystander, andetcetera. In the case of the time machine’s creation, the scientist might getdistracted by a siren or be chased by his dogs.
Personally, I think thephilosopher’s solution to the Grandfather Paradox is convincing because if thetime traveler does not have the freedom to alter the past, there would be no contradiction.Both the traveler and his grandfather can still exist, and the scientist wouldbe able to build his time machine. It defeats the time travelers’ purpose ofattempting murder and destroying the lab but it is the only way to solve theparadox. The accidents that prevent the travelers’ motives makes sense as well.The coincidences that stop the time traveler dismisses the possibility of theparadox. It is a dull, yet simple, solution.
If we considered allowing the timetraveler to murder his grandfather, it would create the paradox, therefore, concludingthat time travel is impossible. There is no way the time traveler and machinecan exist and not exist at the same time. The idea of parallel worlds, thoughit is not Lewis’s, can be a solution to the Grandfather Paradox. According tothe theory, if the time traveler were to travel to the past and change it, the universewould be split into parallel worlds.
One world would be the original where thegrandfather and time traveler is alive, whereas the parallel would be the onewhere both the grandfather and time traveler does not exist. As a result, therewould be no contradiction between the grandfather existing and not existing.