TIME TRAVEL 225
notes, "Should a time traveler who punches his younger self (or vice
versa) be charged with assault? Should the time traveler who murders
someone and then flees into the past for sanctuary be tried in the past
for crimes he committed in the future? If he marries in the past can he
be tried for bigamy even though his other wife will not be born for almost 5,000 years?"
But perhaps the thorniest problems are the logical paradoxes
raised by time travel. For example, what happens if we kill our parents
before we are born? This is a logical impossibility. It is sometimes
called the "grandfather paradox."
There are three ways to resolve these paradoxes. First, perhaps you
simply repeat past history when you go back in time, therefore fulfilling the past. In this case, you have no free will. You are forced to complete the past as it was written. Thus, if you go back into the past to give
the secret of time travel to your younger self, then it was meant to happen that way. The secret of time travel came from the future. It was
destiny. (But this does not tell us where the original idea came from.)
Second, you have free will, so you can change the past, but within
limits. Your free will is not allowed to create a time paradox. Whenever
you try to kill your parents before you are born, a mysterious force prevents you from pulling the trigger. This position has been advocated by
the Russian physicist Igor Novikov. (He argues that there is a law preventing us from walking on the ceiling, although we might want to.
Hence there might be a law preventing us from killing our parents
before we are born. Some strange law prevents us from pulling the
trigger.)
Third, the universe splits into two universes. On one time line the
people whom you killed look just like your parents, but they are different, because you are now in a parallel universe. This latter possibility
seems to be the one consistent with the quantum theory, as I will discuss later when I talk about the multiverse.
The second possibility is explored in the movie Terminator 3, in
which Arnold Schwarzenegger plays a robot from the future where
murderous machines have taken over. The few remaining humans,
hunted down like animals by the machines, are led by a great leader
notes, "Should a time traveler who punches his younger self (or vice
versa) be charged with assault? Should the time traveler who murders
someone and then flees into the past for sanctuary be tried in the past
for crimes he committed in the future? If he marries in the past can he
be tried for bigamy even though his other wife will not be born for almost 5,000 years?"
But perhaps the thorniest problems are the logical paradoxes
raised by time travel. For example, what happens if we kill our parents
before we are born? This is a logical impossibility. It is sometimes
called the "grandfather paradox."
There are three ways to resolve these paradoxes. First, perhaps you
simply repeat past history when you go back in time, therefore fulfilling the past. In this case, you have no free will. You are forced to complete the past as it was written. Thus, if you go back into the past to give
the secret of time travel to your younger self, then it was meant to happen that way. The secret of time travel came from the future. It was
destiny. (But this does not tell us where the original idea came from.)
Second, you have free will, so you can change the past, but within
limits. Your free will is not allowed to create a time paradox. Whenever
you try to kill your parents before you are born, a mysterious force prevents you from pulling the trigger. This position has been advocated by
the Russian physicist Igor Novikov. (He argues that there is a law preventing us from walking on the ceiling, although we might want to.
Hence there might be a law preventing us from killing our parents
before we are born. Some strange law prevents us from pulling the
trigger.)
Third, the universe splits into two universes. On one time line the
people whom you killed look just like your parents, but they are different, because you are now in a parallel universe. This latter possibility
seems to be the one consistent with the quantum theory, as I will discuss later when I talk about the multiverse.
The second possibility is explored in the movie Terminator 3, in
which Arnold Schwarzenegger plays a robot from the future where
murderous machines have taken over. The few remaining humans,
hunted down like animals by the machines, are led by a great leader