Time travel paradoxes appear to be something that can
happen when, in reality, they are impossible even if we allow
for real time travel. Why is that the case? It is simply
because the future from which a time traveler comes will already
be based upon the history that he enters. The time traveler is
a product of the very history that he affects.
An example of this is the presumed paradox that would occur
if a time traveler went back in time and killed his own father
or grandfather so that he would not be born and therefore
couldn’t go back in time to do such a thing. This seems to be a
quandary, but one which is as much of an optical illusion as the
things portrayed in Escher prints.
The simple fact is that if a time traveler exists to travel
back in time he will simply be incapable of killing his father
or grandfather simply because in the past he “didn’t” kill them.
If he tries to kill them he will simply fail because in the past
he already did fail. Literally he can do nothing in the past
which will affect the future (his present) because he is a
product of the very past in which he has become a participant.
This sort of thing was aptly illustrated by a Twilight Zone
TV show where a person travels back in time to kill Adolph
Hitler before he can be responsible for starting WWII. Through
the uncertainties of time travel the female traveler travels
back to the period in which Adolph is a baby. Despite the moral
dilemma the traveler finally chooses to kill the baby and she
herself dies in the process. For a short time we believe that
the traveler has succeeded in killing Adolph Hitler and averting
WWII. Then you find that as a result of the death of the baby a
child is abducted and raised as a replacement for the dead
child. The new baby is renamed Adolph and this abducted baby
turns out to be the Adolph Hitler who becomes responsible for
starting WWII. The time traveler merely succeeded in creating
the very past that she was trying to prevent. That past had to
happen in spite of her actions because it was the past that did
happened because of her very actions. Her actions were simply
unrecorded historical fact leading to the very event she was
trying to prevent.
Another seeming paradox involves the uncreated object.
This is an object from the past, let’s say a coin, which is
taken back in time and given to the time traveler’s earlier self
who will eventually become his future self who again takes the
coin back in time and gives it to his earlier self, ad
infinitum. This coin would have lost any creation point (it is
never given to the person independent of its travel back from
the future). Again, this paradox simply cannot take place
because it never did take place. The coin always has a creation
point otherwise it doesn’t exist to get into this circulating
position. There will have to be an independent arrival of the
original coin in the hands of the time traveler somewhere during
the forward flow of time. When he goes back in time he will
always give himself the original coin from the future that will
then for a while coexist with its earlier counterpart. When the
time comes to take the coin back in time, the original coin that
has now aged will be returned to the past and be given to the
time traveler just as always. The coin that has already been
through the time loop once will not be given back simply because
it never was given back.
So what does all this mean? Well, without the fear of
paradoxes to worry about a time traveler can seemingly feel free
to observe any previous time in history without concern for
having changed anything. This is because the history from which
he springs is in fact the very history in which he was a
participant. If he remembers that Pearl Harbor was bombed on
December 7th, 1941 before he starts his trip to the Jurrasic
period, after his return Pearl Harbor will still have been
bombed on December 7th, 1941. There is literally nothing he can
do that will change this or any other historical event because
the fact is that he has already affected anything that can be
affected.
Time traveling stories seldom concern themselves with the
problems associated with travel to the future and are always
concerning themselves with the problems regarding travel into
the past. Strangely enough exactly the opposite concern may be
more warranted. Since the time the person is traveling to has
not already played out from the traveler’s perspective, anything
he does in the future will affect the rest of time beyond the
point at which he has done something. Quite simply, just the
act of him being there and occupying space may have the
“butterfly effect” that will subsequently cause monumental
things to take place.
Now with the paradoxes of time travel apparently safely
behind us it would seem that time travel is quite safe. Not so.
While it is true that we will not be able to change anything
that is part of our history, it is also true that travel into
the past does have an affect on history, our present and
possibly even our future. Just as in the attempt to kill
Hitler, the time traveler can inadvertently set things in motion
in his history that he has no idea that he is responsible for.
In the mid 1300’s the Bubonic Plague spread from China
throughout Europe and killed about 25 million people. Let us
consider that in the year 2310 a virus mutated from a relatively
benign form into the one that causes the Plague. Then in the
year 2311 a time traveler wishes to study the spread of the
Plague from China and makes arrangements to go there and study
this as part of preparation for his doctoral thesis. Everything
is set in motion, but just before the time trip the traveler is
exposed to the mutated virus yet does not show any symptoms that
would prevent him from making the trip. He then travels back to
1346 when he becomes ill and infects others around him.
Realizing he has contacted the Plague he signals that he needs
to return to his own time and is transported back to 2311. Sure
enough he has the Plague, but the medicine of the time is well
advanced and is able to cure him. However, 25 million other
people are not so lucky and die in the mid 1300’s directly
because of his trip. The traveler doesn’t even know he is the
cause and assumes he simply had the bad luck of contacting the
disease in 1346 just like many of those people. There is no
paradox (the death of 25 million people is historical fact), but
the traveler has just caused the death of 25 million people
simply because he traveled to their time. If he had not
traveled to that time they would not have died, yet the fact
that they did die in the traveler’s history has doomed him to
cause their death inadvertently.
So, now let’s wonder for a moment if the extinction of the
dinosaurs was a time travel accident? Who is to say that the
“asteroid” 65 million years ago wasn’t really the reactor of a
timeship that went critical during a crash landing? Of course
it used an Iridium power core.
So, clearly, time travel is not without its pitfalls. The
only saving grace is that the historical disasters have already
happened. In this respect time travel to the very recent past
is possibly more of a concern since the effects of such trips
may not have had a chance to reveal their full potential
consequences. Trips to the more extreme past, on the other
hand, have likely already produced any truly undesirable effects
and would be part of the traveler’s known history (Bubonic
Plague, extinction of the dinosaurs, etc.).
A related concern is travel of a person at faster-than
light speeds. Time and time again (pun intended) such travel is
stated to result in the traveler going back in time (i.e., a
time machine effect). A simple thought experiment illustrates
how preposterous this idea actually is.
Let’s presume for a moment we have a ship capable of
traveling at many multiples of the speed of light and that we
can survive travel at such velocities. Now we decide to take a
little trip across our galaxy (about a 100,000 light years).
Let’s say for the sake of argument that travel time is
instantaneous. We step into the ship and press the GO button
and presto we are on the other side of the galaxy. In this ship
we have traveled at infinite velocity relative to normal spacetime
and we are on the other side of the galaxy. Now if we had
an amazingly good telescope we could look back at earth and see
just what it looked like 100,000 years ago because the earth
light from 100,000 years ago is only now reaching our current
location. However, we have not traveled backward in time. On
earth it is still just an instant after we left and to us it is
still an instant after we left. No time travel has taken place.
We can view the past, just as scientists do everyday with
telescopes, but we are no more capable of altering events in the
past than scientist can alter events they are observing every
day.
Then we jump back into our space ship and press the RETURN
button and, abracadabra, we are back at our starting point just
moments after we left. Earth has not aged eons nor have we
traveled anywhere in time.
Now the situation I describe does not apply to travel at
speeds just below or even at the speed of light. In those
cases, travel to us would be near instantaneous or at least
reasonably fast while eons would pass on earth before our
return. What I am describing above is travel outside of normal
space-time in an environment where the speed of light is a
meaningless concept.
Making time travel possible begins with understanding that
time does not exist independent of space and visa versa. Time
only exists within the context of space (distance) and space
only exists within the context of time (how long it takes to
traverse distance). Both time travel and instantaneous space
travel would come about by exiting space-time and then reentering
it at another location (a different combination of
space and time). However, exactly what is required to exit
space-time is unknown. Also, assuming that one manages to exit
space-time, what is required to re-enter space time
elsewhere/elsewhen is also unknown. It is also unclear whether
we could survive the attempt. Our bodies would appear to depend
upon being imbedded in space-time for our very existence. So,
one might assume that we would have to make this jump from
place/time to place/time within some kind of space-time bubble
that would allow us to survive the journey. Essentially we
would be taking a little self-contained piece of universe with
us on the trip. Also, the ability to navigate to particular
space-time coordinates while being external to space-time is
likely to be an interesting trick.
To navigate to particular space-time coordinates while
outside of space-time would seem to require some kind of sensing
system that can transcend the space-time boundary in some way.
Otherwise we might have to understand how space-time looks from
“outside” in the same way we can view a three dimensional wooden
cube from outside. The problem with navigating to space-time
coordinates from “outside” is that no one knows what space-time
“looks like” from that vantage point. We are essentially in the
same predicament as a termite in a wooden cube trying to
envision what his wooden home looks like without leaving it.
Though we are a little more intelligent than a termite (at least
sometimes), determining how to sense the size and shape of
space-time from within would prove daunting. We can only hope
that from “outside” things might become a little more obvious
just as the shape of the block of wood is to us when viewed from
the outside.
Will time travel or faster-than-light travel ever happen?
Whatever humanity has imagined we eventually succeed in
achieving. Perhaps it is just a matter of time.
