Time travel is the concept of being able to

Time travel is the concept of being able
to travel in between certain points in time, whether it be to the past or the
future. In many movies and books, people often travel though time machines in
which they can take the form of doors, vehicles, portals, and so on. An example
of time travel would be where one steps into a time machine and arrives at a
destination 30 years before or after the initial timeline. It would not be considered
time travel if someone were to turn his clock back two hours: the person did
not physically go back two hours of that day. He simply changed the time of the
clock. It is unknown if time travel is possible but as of now, it is highly

According to American philosopher David
Lewis’s article, “The Paradoxes of Time Travel”, time travel involves “a
discrepancy between time and time” (Lewis, 1). To elaborate, if an Irvine
student were to get in his car and drive to Los Angeles, the time it takes from
the starting point to the destination would equal the time of the journey.

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However, for a time traveler, the separation in time between leaving and
arriving would not be the same as the period of his journey. For example, an
hour spent in the time machine does not mean the traveler is an hour ahead of
the present: it could be days or months into the future.

            The Grandfather Paradox is a contradiction
of time travel in which an inconsistency occurs in trying to change the past. The
main problem of it is this: A time traveler goes back in time to change the
past but it is impossible to alter it, and since the past is unchangeable, time
travel must be impossible as well. According to the lecture, the Grandfather Paradox
occurs whenever a time traveler goes back in time and “prevents an event that
is a pre-condition of the traveler making the backward time-journey in the
first place” (Bernecker, Grandfather Paradox, slide 1). Take, for example, the
scenario used in lecture: (Premise 1) A time traveler goes to the past to kill
his grandfather. (Premise 2) However, if he kills his grandfather, he cannot
exist 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 is
unable to go to the past to kill his grandfather. The Grandfather Paradox
questions whether or not we can travel to the past and change it. The main
worry of the paradox is that it would be impossible to kill the grandfather
since it violates the law of non-contradiction: the grandfather somehow both
survives to have kids and cease to exist. The time traveler cannot really
change the past since his grandfather exists in the present, hence the time
traveler’s current existence. Premises 1 and 2 contradict each other so it must
mean that backwards time travel is not possible. Technically, the time traveler
can murder his grandfather since he
is currently living but because it would get rid of one of his parents and
himself, he can’t travel to the past. Despite the name, the Grandfather Paradox
does not specifically have to involve the contradiction in murdering one’s
grandfather to prevent one’s own birth. The paradox can involve anything that
alters the past, since there is an inconsistency whenever the past changes from
the way it was.

Take another example of the paradox: A scientist
goes back in time to destroy his laboratory to prevent himself from building a
time machine. He succeeds in destroying the lab but what about his invention of
the machine? The past version of the scientist would not be able to build the
time machine that would allow him to go back to destroy the lab. The scientist
has no method of travelling to the past and thus, time travel would be

            Lewis was known for his thoughts on
the possibility of time travel and mostly, for his solution to the Grandfather
Paradox. He mentions the paradox in “The Paradoxes of Time Travel” and the
solution he provides to it is one that shows that the “paradox” is not really a
paradox. Lewis says we must assume the time traveler cannot change the past
even though he can take part in it. The freedom of the time traveler must be
limited since the past is fixed. He also says there must be strange
coincidences that prevent the past from changing. For the grandfather scenario,
the time traveler would not be able to murder his grandfather due to the
jamming of his gun, shooting someone else, being stopped by a bystander, and
etcetera. In the case of the time machine’s creation, the scientist might get
distracted by a siren or be chased by his dogs.

            Personally, I think the
philosopher’s solution to the Grandfather Paradox is convincing because if the
time 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 would
be able to build his time machine. It defeats the time travelers’ purpose of
attempting murder and destroying the lab but it is the only way to solve the
paradox. The accidents that prevent the travelers’ motives makes sense as well.

The coincidences that stop the time traveler dismisses the possibility of the
paradox. It is a dull, yet simple, solution. If we considered allowing the time
traveler to murder his grandfather, it would create the paradox, therefore, concluding
that time travel is impossible. There is no way the time traveler and machine
can exist and not exist at the same time. The idea of parallel worlds, though
it is not Lewis’s, can be a solution to the Grandfather Paradox. According to
the theory, if the time traveler were to travel to the past and change it, the universe
would be split into parallel worlds. One world would be the original where the
grandfather and time traveler is alive, whereas the parallel would be the one
where both the grandfather and time traveler does not exist. As a result, there
would be no contradiction between the grandfather existing and not existing.


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