When one reads Science Fiction there
is hardly anything so fascinating and yet so frustrating as the
'Time Travel' story. Fascinating, because it often explores the
question 'what would things have been like if...?" or "if
one could change a small thing like the position of a grain of
sand would that have large effects in the future?". These
questions are at the heart of personal or historical regret. Suppose
Hitler were never born. Would this be a better or worse world
today? Would it be a different world 100 years from now or would
the forces of history push towards a singular result?
The stories are often frustrating due in part to a vaguely spelled
out theory of time which often allows events that are confusing,
contradictory and paradoxical. A science fiction story should
not leave us with more questions than it resolves. For a reader
of Fantasy, this may be acceptable, for Fantasy is not supposed
to be taken as explanatory, prophetic or possibly realistic. But
a good science fiction story should have explanations that are
not incoherent and if in the story there is something which is
claimed to be impossible, then there should be an explanation
for that also.
At the heart of the problem is the 'Time Travel paradox' which
goes something like this. Suppose a person travels to a time before
she was born and breaks a causal chain that led to the traveler's
birth. This problem has been commonly explored by asking 'What
if you killed your own grandmother before she first conceived?'
(Curiously the problem is never expressed in terms of killing
your own mother). The apparent paradox is then of a logical sort:
P entails NOT P and NOT P entails P. If you kill your grandmother
then you would not be born, which in turn would bring it about
that you not travel into the past, thus you would not kill your
grandmother, thus you would be born causing you to again travel
into the past to kill your grandmother.... ad infinitum.
The presupposition of almost all time travel stories is that each
point along a time line is in some sense existent now, even the
future points. This provides a conceptual basis for allowing us
to visit a time point in the same way that we might visit a space
point in ordinary experience. Einstein may have reinforced our
comfort with this view by taking seriously the notion of time
as another dimension very much like the spatial dimensions we
are already familiar with.
There are several different standard attempts to resolve or avoid
the paradox. The most standard is to ignore it. By sending someone
far enough into the past, we do not know what influence that person
will have and thus for all we know the person caused the world
as we know it today. Another way to avoid the paradox is to state
up front that we cannot change the past. There are different versions
of this thesis. One is that we can go back and participate in
a past causal chain but only in the way that already happened
and the other way is to go back merely as an observer.
Some stories entertain the notion that you can go back and change
things, but not those things that would lead to paradox. I would
like to put forth the view that there is something wrong with
all of these approaches and that the only view which is successful
at resolving the paradox is an alternate universe theory of time
travel which we shall explore momentarily. Such a view was expressed
in "The Terminator" in which a character from the "future"
confesses that maybe he just comes from a "possible future
" not the actual future of this time.
When a time travel event occurs, it is helpful to see that it
may be one of two kinds. Take, for instance, a "traveling"
from time point c to time point b, where c is later than b. Either
we are sending an object to a time and place where it already
was and it is the same object in every respect as that object
in that time and place or we are sending it to a place that it
wasn't or at least wasn't in that exact state. Let us consider
the second possibility first.
Supposing that the object wasn't at b but we intend to send it
there anyway. If we are successful then we have created a contradiction,
for it becomes clear that when the time travel event occurs it
becomes true that the object was at time point b and yet it was
false that the object was at b. This is an impossibility if we
take any standard linear view of time. The most minimal means
to accommodate this contradiction is to allow a timeline where
the statement that the object exists at b is true and another
timeline where the statement that the object exists there is false
(the 'original' timeline.). In other words a timeline branching
event has occurred. Any story that holds that the object was not
on the timeline and now it is, is minimally committed to this
branching universe concept. See Figure A...
This does not mean that a story must subscribe to the view
that there are two existent timelines or Universes. The story
may hold that the "original" time line b-c-d no longer
exists, if it ever did and so even though we may conceptually
represent the time travel event as above, some may claim that
b-c-d no longer exists.
This way of talking about the time travel event makes it look
as if 'first' the universe was linear, and then as soon as time
point c arrived the universe became more complicated. But this
way of describing it makes it sound as if there is a time when
the object was not at b and then there is a time when the object
was at b. What kind of time is this? It seems that we may express
the same concept by noting that the object at c is the cause of
the branching of timelines at b.
My position is that any coherent time travel story may be accommodated
with the above diagram. There are various positions one could
take regarding the existent or non existence of these time line
segments that will provide the accommodation. We may even find
it important to relativize existence to each point. For instance,
we may imagine a story that claims that from the viewpoint of
a person at point e timeline b-c-d does not exist. We can also
image that there might be 4 possible stories about a person at
time point a. The story may claim that for that person b-c-d exists
but not b-e-f, or vice versa, or that both exist. One might even
claim that time-travel has rendered neither existent, although
this story might not be the common one. (There was a Fredric Brown
story that had this as a punchline)
Although relativation of existence to positions on the timelines
is not my favorite way of displaying these notions it at least
allows for the description by a person at e that b-c-d used to
be existent but now it isn't. This might only mean that for a
person at a, bcd is existent but for a person at e, bcd is not
existent.
This branching universe notion even accommodates the time traveler
who cannot change the past, for such a view can be expressed by
saying that bcd is always identical with bef. But such a story
must in order not to be self contradictory only send objects to
places where they already were, otherwise we risk having it be
true that an object was there and at the same time be false. A
writer cannot have it both ways. She cannot make a change in the
time line and then insist that there is and always was only one
timeline. A contradiction is not to be tolerated in a science
fiction story since it breaks down the credibility that a science
fiction story needs to not be merely fantasy.
The first thing we should note is that there is no paradox
within the above understanding of time. If a traveler from point
c returns to space-time point b where she did not exist before
and causes a branching she then proceeds to travel down the new
branch bef (unless another time travel event occurs). She is now
free to bring about the non-existence of her analogous self on
time line bef. If she does succeed in interrupting the causal
chain that as analogous to the one that happened on line bcd that
brought about her own existence and if this results in the non
existence of her analogous self then of course her analogous self
will not journey into the past causing another split in time.
This in no way affects the existence of the traveler who left
time point c, only the possible development of her analogous self.
In fact, it may be conceptually messier if she allows her new
self to take a similar trip, for if this continues, we might see
an infinite number of branchings at point b each caused by an
analogous self traveling into the past. This is not a serious
problem, its just messy. There are other conceptual problems in
time travel stories that should be addressed, namely the problems
of associated with rewriting history.
In so many stories, the traveler goes to a place in the past
so as to change some event that will alter the future. This was
the job of the terminator in Terminator 1. His task was to kill
the mother of his enemy before she conceived. But now let us ask
"what would this accomplish" According to our model,
the terminator, if successful, travels from c to b and kills his
enemies mother. The terminator then proceeds to lead a quiet little
life on time branch bef. But has he changed the place from whence
he came? If we hold that both timelines are equally existent then
it seems that the entities that sent the terminator at best only
created an alternate universe where their enemy doesn't exist.
The original timeline will proceed as it would without change
except for the loss of one terminator who has left to occupy an
alternate time line. It is hard to imagine the motivation of these
entities in the future to create such branching events since from
their viewpoint all they have accomplished is getting rid of a
well trained killing machine that was on their side.
To increase the stakes in such a story we somehow must conjecture
that there is only room for one timeline, which is to say that
timeline bcd or some portion of it becomes non existent and is
replaced by the new timeline with the analogous beings.
So we have the view that first time proceeds down path abcd and
then it later gets replaced with path abef. So in terms of figure
A, the time between a to b is always existent. The time between
b and c exists earlier but becomes non existent, and the time
between b and f becomes existent. Something like this view seems
to be present in most of these stories.
It may be that the viewpoint of the author is that bc stays existent
and what disappears is the time line cd. Either of these views
gives the beings on timeline bcd something to worry about because
either their whole existence will be replaced with analogous beings
or their world after the traveler leaves from c will be erased,
in which case their future has been eliminated.
The primary problem with asserting that the time between b and
c becomes non existent is that from the viewpoint of someone on
the timeline bef, a possibly crucial change in history was made
by an entity which was created by things that never existed and
never will exist. So some existent things are causally brought
about by non existent things. If a story is committed to this
view, then reality becomes filled with possibly existent objects
that under certain circumstances enter into causal chains and
affect the actual world. This view does damage to what we usually
think of as existence. That is, we would usually subscribe to
the notion that anything that enters into a causal chain with
the real world is part of the real world, i.e. existent. I would
wish to reject this view and would propose that we grant the existence
of any world or timeline that causally affects our world.
Some may object that sometimes non existent things do affect existent
ones. My vision of a freer society in the future may affect the
future. But it important to note that my vision of a freer society
is not caused by the freer society but by my vision and my vision
is existent.
But let us overlook this problem of causality associated with
this non existence for a moment and ask a few more questions.
If time travel is understood by those with the time travel device,
what is their motivation for wanting to eliminate their own timeline
and replace it with another one with analogous beings on it? They
might believe that the other world is a better world and thus
they are willing to be destroyed to have the world replaced. In
this case their altruism is to be commended.
Or maybe they believe that by destroying this world, their essence
of being is transferred to those analogous beings, except for
the time traveler of course, for there could be two of her on
the new timeline. The time traveler and her counterpart should
be regarded as similar but not the same being. Furthermore, beings
that exist in the first timeline but not in the second would not
be transferred. But I think we should realize that this breaks
again with the notion of science fiction and enters into fantasy
unless the writer is willing to supply us with scientific reasons
why such a "soul transfer" happens.
Another question we may ask within this view of one timeline being
replaced by another is at what point does it happen. The standard
view, which seems totally incoherent, is that it happens when
the traveler makes the important change. But we have seen that
an important change is made when the traveler first arrives at
b. This is the first moment when the world is different than it
once was. This is the moment where the timeline splits. If the
view of those trying to change the past is that the world as they
know it becomes non existent, then there is only one time that
should mark the termination of their timeline, the moment that
the traveler leaves on her trip, time c. Thus it makes no sense
for another traveler after time point c to go back and "prevent
the change", since all the time on timeline bcd has become
non-existent when c occurred. This unfortunately happens in too
many stories, i.e. Timecop, terminator, etc.
Sometimes I think the writers of such stories are deliberately
unclear on their theory so that they can get away with more. But
maybe in many cases the writer hasn't thought the idea out clearly
enough to understand it herself. I am not asking that the writer
build a time machine but only that they have some clear idea of
what it is supposed to do.
If we take my view, that if time travel is possible and changing
the past is possible then both timelines are equally exist, we
have lost many of the standard motivations for going into the
past, but not all. For instance, suppose you believed that this
world is much worse off than it would have been if, say, the atomic
bomb were not invented. Suppose you believe that with a time machine
you would have the ability to change a sequence that led to the
development of the atomic bomb. You could then go back and make
the change, and after such change proceed into the future along
timeline bef. This would be the world without the bomb, if you
had done your work correctly. You could now live there, although
it might be a little crowded with the two of you, unless you can
convince the other of you to build a time machine and leave.
The people that you knew would still be back on the other time
line. Maybe similar ones would be on your new timeline, maybe
they wouldn't, but you couldn't go home again. Or could you?
What conceptually would prevent the development of a inter-timeline
travel device? Nothing really. So, for instance, after your work
is done you may decide to move back to a time right after you
left. See figure B
A semantical problem becomes apparent. You tell your friends
about your time travel venture and how you changed the past. Should
they believe you? No. Nothing has changed. The past is still as
it was. The atomic bomb still exists. But the problem is in the
language. In a sense you did not visit your own past, but instead
a past similar in every respect except for one thing, you were
there. From that point the universes diverge and you are in a
place even less like your own past. So, should we call this time
travel or is it more appropriate to call it timeline creation
or alternate timeline visitation?
It does have some resemblance to time travel as we usually think
of it, though. For instance, if you didn't affect things too much
you could go back and confirm or disconfirm historical records.
The extent to which you did affect events would be the extent
to which you couldn't be sure that that is really the way it happened
on your original timeline. For my part, it seems to be enough
like visiting another time so that it does not seem inappropriate
to call it "time travel".
All of the considerations here are equally applicable to time
travel events with mental objects instead of physical ones. For
instance, suppose you wished to correct a regrettable action.
Some stories may hold that you could transfer your mental makeup
into an earlier self and do something different. But if by doing
so, things become different than they originally were then a timeline
split again is the result and the most we can say is that you
have moved to the timeline where your regrettable action did not
take place. The people on the new timeline will not blame you
for your mistake, but the people on your original timeline still
do. In the writing of the story, it would be interesting to wonder
if this timeline move should be enough to get rid of your regret,
since you still remember what you did on the home timeline.
Most of our discussion has been about time travel events that
change the timeline, but let us for a bit consider stories where
the traveler is sent to a place and time where she originally
was. These stories usually have the traveler going into the past
and then we later confirm the event by discovering some evidence
of her existence at that past time. (Somewhere in time seemed
to be such a story. I would like to argue that this is not an
example of a science fiction story but instead represents a fantasy.
I have several reasons for this position.
Suppose a traveler is sent to yesterday, to a place where it was
noted that this traveler appeared. Upon her appearance, we started
taking notes of exactly how she moved, when she stood up, when
she sat down, when she raised a hand and what she said. In this
story, let us give all of this information to the traveler before
she is sent. Now let us look at the story from the traveler's
point of view.
She arrives and she knows exactly what she is going to do. She
cannot move in anyway different from what she knows she is going
to do. In every respect she is a person trapped in an uncontrollable
body. What is the explanation for this? Why can't she move contrary
to what she knows will be the case. Why can't she cause a time
branching event? The story owes us an explanation and if it is
a science fiction story it cannot just be "well, that's the
way it originally happened" In science fiction we need some
hint at the force that is making it come out that way. How are
we to explain the lack of will? Is it the Gods forcing her to
do it? Fantasy. Is she just a passive rider in the body? Then
who is making her body move the way it does?
Maybe, every time we send someone back, they lose their memory
and thus they do what they would naturally do with no feeling
of force. If this is true, we need an explanation for why the
memory disappears, and the explanation should not be that this
solves the problem of free will. As fantasy, this would be acceptable,
but in science fiction we should receive an independent explanation.
In many of these stories, the traveler only partially knows the
future and every attempt to change it usually ends up part of
the fulfilling of the future instead. Are we to imagine that every
time travel event happens in this way? If so, then they cannot
be the result of a scientific device that makes time travel happen.
Let me give an example. Let us with our time travel device send
an object, a marble, from 12:05 P.M. to 12 noon. First of all,
we should only send this marble after we notice that it appears,
otherwise we know that such an experiment is bound to fail. So
we wait until 12 to see if it appears. Sometimes when we do this
experiment it does appear and sometimes it doesn't. What determines
when it does, some scientific principle? After we understand this
principle we should be able to make it work every time just by
being in accordance with the principle.
So it appears in front of us. Now let us suppose that at 12:01
we decide to not send the marble. Can we do that? If not why not?
Is it a scientific principle or is it the gods again. If the latter,
then we do not have a scientific time travel device but one that
is dependent upon the mystical forces of the universe.
Another consideration is brought about by asking the question:
"Is it really the same marble?". After all, some very
accurate dating device, maybe like carbon dating, would show that
the object that left was 5 minutes older than the object that
arrived. If they were the same object, then the object that arrived
would be a few moments older than the object that left. But we
can see that this is impossible. Are we to image that there is
some force that makes the marble younger as it goes back in time,
just to make things work out? Again it appears the mystical forces
are at work.
Instead of deciding not to send the marble back, let me propose
a different experiment. Let us take the marble that appears at
noon and make that the object that we send back. It disappears
at 12:05 as planned. Questions arise. Where did this marble come
from in the first place? This question will not get a satisfactory
scientific answer, not even a satisfactory pseudo-scientific answer.
It cannot be in terms of how the time travel device works. Again
the answer must lie with mystical forces.
So the conclusion is that time travel of the sort, where the object
is sent to a place that is identical to where it was, is not of
the sort that science could claim credit for. Thus, it could not
be a main subject of a science fiction time travel story. It might
do well in a story of fantasy. And I say this without any derogatory
implications about fantasy. I enjoy a good fantasy as much as
the next person, but we should realize that in a fantasy many
questions of explanation are inappropriate, but in a science fiction
story they are quite at home and indespensible.
So now let us suppose that we are conducting our life in an
ordinary way when all of a sudden a being who claims to be from
the future materializes in front of us. How should we interpret
the meaning of this phenomenon?
To back up a bit, we should realize that such an experience is
conceptually possible, especially if we state the description
of it in subjective terms. "It seems that someone has suddenly
appeared out of nothing. He claims to be from the future."
It is even possible that he believes he is from the future. Now
let us suppose that we believe he believes he is from the future,
and furthermore, he shows us how to create some technology that,
as far as we know, has not been invented yet. All of this experience
is not conceptually impossible, but now it is up to us to figure
a reasonable interpretation for it.
Suppose furthermore, for some reason we decide that the explanation
we are willing to consider does not involve alien deception, our
hallucinations, our dreaming, some mind controlling experience
implants, etc. In fact, let us say that we are only willing to
consider two explanations. First, that he is from the future,
our future, the way it is going to be and there is no way to change
it, or he is from our future the way it would have been if he
hadn't come back and caused a timeline split. If it is the second
then we merrily proceeding down the path bef of make our future.
(While our counterparts, who did not experience the appearance
of the traveler are moving down the original path bcd to bring
about the beginning of the traveler's journey).
I would like to suggest that the way we decide to interpret such
an event will depend upon to what extent we believe the universe
is subject to mystical forces verses so-far-undiscovered-scientifically-explainable
forces. In other words, is this witnessed event the result of
our world behaving like a fantasy or behaving more like science
fiction?
If we choose the first, we may very well think of the traveler
coming from our future and this future cannot be changed. If he
furthermore tells us that we are all going to raise our hands
in 5 seconds and even though we try not to we do anyway, then
we would have confirmed that mystical forces our governing the
situation. There would be no problem of free-will since, the fates
will have rendered free-will an illusion. Furthermore, it would
probably render the notion of explanation also one of illusion.
But if we are committed to the notion of explanation, we must
interpret the apparent event as one with a scientific explanation
(maybe not explicit), leaving enough order in the universe to
render explanation meaningful. Then we can regard ourselves as
free to use the information the traveler provides us to change
our future to our liking. If the world that (s)he came from is
undesirable and (s)he gives us the information necessary to change
it then there is nothing except for the natural forces already
in play to prevent us from doing so.
So in conclusion, I would like to recommend to any Science
Fiction writer that thinks (s)he is writing science fiction that
that (s)he use the timeline branching framework, without which
the author risks contradiction and thus incoherence. Furthermore,
if the author wishes to claim that the future that created the
traveler no longer exists in order to blow the mind of the reader
with paradox, (s)he should realize that the source of the paradoxical
feel of the story is this very claim. The reader can easily dismiss
the mind-boggle feeling by noting that the author is committed
to an awkward theory of existence.
So let us write good Science Fiction Time Travel stories, make
them fun and exciting but please let's also make them understandable.