Paradoxes
Everything
that can be invented has been invented. -Charles
H. Duell
(1899)
Time travel, as
presented in movies and books, results in a variety of
paradoxes. The most famous paradoxes surround the tendency
of people to want to change things in the past. Forward time travel
offers some interesting implications of its own. Just
as today is affected by the events of
yesterday, so must the future be affected by the events of today. The
future
has not been decided yet. Therefore, it becomes possible that merely
attempting
to time travel to future years has a significant effect on the way that
the
future will eventually be.
Below is a brief explanation of some of the better known paradoxes
including the grandfather parardox,
the free-lunch paradox, the twins paradox, and another question.
Backward
time travel
The
Grandfather paradox
The
grandfather
paradox, perhaps the most well known of time travel paradoxes, becomes
a
possibility with backward time travel.
If I decided to go back in time and kill my grandfather before
he had a
chance to conceive my mother or my father, then I would no longer exist. But if I no longer existed, then I could not
have killed my grandfather so he would be able to conceive my mother or
my
father. This would lead to my existence,
again allowing me to kill my grandfather.
Thus, a time loop is born in which I am perpetually killing my
grandfather and being born; it becomes a circular problem. This
also manifests itself in other ways. For example, in Back to the
Future II, when Biff steals the Sports Almanac in 2015 and gives it
to
himself in 1955, he begins a variation on the grandfather
paradox. Biff has Doc Brown committed before he could invent the
time machine. That would make it impossible for old Biff to go
back in time to give himself the Sports Almanac. It creates
another loop.
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The
Free-Lunch paradox
The free-lunch
paradox also arises from backward time travel. It suggests that
if I
were to travel back in time and present Beethoven
with all of the piano sonatas that make him famous today, and he, in
turn, copied
the sonatas from what I showed him, then the sonatas exist only because
I went
back in time and Beethoven never composed them in the first
place.
This creates another loop because the sonatas only exist due to my
decision to travel back in time. This can be seen in the novel The Anubis Gates
by Tim Powers. Brendan Doyle memorizes "The Twelve Hours of the
Night"
in 1984, and he writes it down in a coffee shop in 1815. In doing
so
he becomes the poet, but that can only be possible if he travels back
in time. So the poem's existence rests upon Doyle's ability to
travel
back in time.
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These
paradoxes can be resolved in several ways. One
theory is that in traveling back in time, one might actually travel
to the past of a parallel universe; so, for example, in one universe
one is
born and decides to go back in time and kill one’s grandfather, but in
another
one arrives back in time and actually does kill him preventing one’s
birth. Another theory provides that nature
would
contrive a way to prevent the traveler from changing the past: “What
has
happened has happened. It cannot be
changed[;]…it cannot be repeated twice in different ways” (Nova). Time travelers could not, therefore, rewrite
history.
Forward Time Travel
The Twins
Paradox
Forward
time travel could further lead to something known as the twin paradox. The twins paradox is based upon Einstein's
Theory of Relativity. If one member of a pair of identical
twins
were to orbit the earth at close to light speed for a few hours, when
he
returned to earth, he might find that his twin had aged several years. Taking advantage of this theory leads to one of the theories
about how time travel could work. This
paradox does not prevent
forward time travel from being a very plausible notion.
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Another question
Another
important question is raised if time travel to the past is possible—why
aren’t
we meeting time travelers from the future?
Some obvious solutions present themselves. Visitors
might be here without our knowing
that they are present. Backward time
travel might be possible, but human civilization might destroy itself
before it
can ever be invented. Another idea is
that it may be impossible to travel backward to a point before time
travel was invented.
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