Living in the Now: Is This All There Is?
There is an alternative to eternalism and the growing-block universe that also takes seriously the idea that there is something very different about past, present, and future. This is “presentism,” the view that only the present exists.
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For the presentist, the totality of reality is a thin sliver of space-time that is a single instant of time. No locations in the past or future exist. This theory explains why the present seems especially real to our perception: it is the only real moment.
One reason we might find either the growing-block model or presentism more attractive than eternalism is that both of the former views seem to allow that the future is not fixed. If the future is
already
sitting out there in space-time somewhere, then it looks as though what happens in the future is already fixed. But if the future is not yet real, then we might make sense of Kyle’s message to Sarah that the future is not fated and can be whatever we make it.
Could the
Terminator
universe be one in which the growing-block model or presentism is true? It might seem that eternalism must be true. After all, 2029 must already exist for those living in 1994 if the Terminators are to travel back in time from it. But actually, that doesn’t really follow. That moment in 2029 when the T-101 activates its time-travel device has to exist
when that moment is the present
, but that doesn’t mean it has to exist as of 1994. The idea here is that traveling in time might be different in important ways from the manner in which we usually think about traveling across space. Suppose that someone is traveling from A to B. Then A must exist
when the traveler leaves from A
, and B must exist
when the traveler arrives at B
, and the intervening locations must exist
when the traveler travels through them
. But—and this is the important bit—B doesn’t need to exist
when the traveler is at A
, and A doesn’t need to exist anymore
when the traveler reaches B
. These spatial locations need to exist only when the traveler is
there
; from the traveler’s own perspective, whenever she is “here” at a location, of course that location must exist. Of course, we don’t think that locations in space actually wink in and out of existence. But if either presentism or the growing-block model is correct about which locations in our universe exist, and if time travel from the future is possible, then locations in time
must
be like this.
The idea is that when Terminators leave 2029, that year is the present and it exists. They arrive in 1994, when that time is the present, and, of course, it exists. The fact that when 1994 is the present, 2029 does not yet exist does not matter, just as long as 2029
will
exist in the future, so that when it
does
exist, the Terminators can travel back to 1994. On the growing-block model, 1994 has already existed for thirty-five years when 2029 rolls around, so once 2029 is the present, the Terminators can happily travel back to a location that exists even relative to their current time.
But we get a different result if presentism is true. According to the presentist account, when 2029 is the present, 1994 does not exist. But that does not matter, so long as 1994
did
exist, so that the Terminators can travel back to 1994 when it
was
present. If presentism is true, only the origination or the destination of the time-travel journey ever exists at any moment, and never at the same time.
Remember the differing sentiments of Reese and Sarah Connor that we started with? If either the growing-block model or presentism explains time in the
Terminator
saga, then we might have a way of reconciling the two sentiments of the story. Sarah decides to kill Miles Dyson to prevent Judgment Day, by stopping Skynet from ever coming online. If the growing-block model or presentism is true, then the future does not exist. But if the future does not exist, then perhaps it makes sense for Sarah to try to prevent Judgment Day from happening.
Unfortunately, matters are not that simple. Even if the future does not exist, certain claims about the future
could already be true
in the present. Suppose 1994 is the present. Simply by the fact of a T-101 arriving from 2029, we’d have to conclude that Judgment Day will occur in 1997. But if a Terminator traveling back in time changed history, preventing Judgment Day by helping Sarah to destroy Dyson’s work, there would be no intelligent machines in 2029. Then there would be no Terminators to travel back in time. This would be paradoxical, and a paradox
does
imply a logical contradiction.
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Philosophers call this the grandfather paradox. It can’t be true both that there are time-traveling Terminators and that there aren’t any such Terminators. More generally, the idea is that if I were to travel back in history, I could not, for instance, kill my earlier self, or my grandfather, because then I would never come into existence in order to travel back in time. So even if I could travel back, I could not kill my grandfather.
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For the very same reasons, the T-101 cannot bring it about that there is no Judgment Day. That is, the T-101 cannot bring it about that there is no Judgment Day because to do so would mean that the T-101 itself does not exist. So the grandfather paradox gives us additional reason to suppose that it is true, in 1994, that Judgment Day occurs in 1997. But if that is already true in 1994, then it looks as though the future is fixed: Judgment Day really
is
inevitable and nothing Sarah and John can do will have any effect on the future.
Although this seems like common sense, there are good reasons to believe this conclusion is false. Suppose it is true, in 1994, that Judgment Day will occur. Does this make Reese’s message to Sarah about making our own fate untrue? It certainly doesn’t mean that Judgment Day is inevitable, in the sense that it is fated to occur and so we are powerless to stop it. To see why it doesn’t mean this, consider this analogous example: if it is fated that Sarah will recover from her “mental illness,” then, regardless of whether she consulted a doctor or not, she’ll recover. Either it is fated that Sarah recovers, or that she does not. If she is fated to recover, then she will recover whether she sees a doctor or not, and if she is fated not to recover, then she won’t recover even if she sees a doctor. So either way, seeing a doctor will make no difference to whether she recovers. But this reasoning is unconvincing,
because
it might be that Sarah recovers
because
she sees a doctor. In that case her actions make a difference as to whether or not she will recover.
Judgment Day: Is the Future Fated to Happen?
We need to be very careful when we talk about the inevitability of some future event and our ability to affect that future. It might now be true that Sarah will recover from her “illness,” but that does not mean that her actions have no effect on being evaluated as sane. It might now be true that she will recover,
because
it is now true that she will take her medication, play well with others, and avoid stabbing her therapist in the knee. Similarly, it is not that Judgment Day is fated, in the sense that it will happen no matter what anyone could have done. Judgment Day happens
because
of the actions that humans take, including Sarah’s own actions. If people had acted differently at various times, then things would have gone differently, and different facts about the future would have been true in 1994. So Judgment Day is not inevitable; some other set of facts about the future could have been true in 1994. Yet one of the facts that
is
true in 1994 is that Judgment Day occurs three years later.
This does not mean that between 1994 and 1997 people somehow lose their free will, or lose their ability to affect the future. It means that what they do between 1994 and 1997
brings it abou
t that in 1997 Judgment Day occurs. So what Sarah and John should conclude when they learn various facts about the future isn’t that they can’t affect the future, but that
whatever they do that affects the future is part of the cause-and-effect story of why Judgment Day occurs
. Sarah shouldn’t conclude that she can’t affect the future, but she should conclude that she cannot change the future from the way that she knows it will be, to it being some other way. If it is a fact in 1994 that Judgment Day will occur in 1997, then Sarah can no more change that fact about the future than she can change the fact that in 1984 a T-101 tried to kill her.
In
Terminator 3: Rise of the Machines
, we learn that Sarah’s hopefulness was not misplaced: her actions in the previous film have changed the date that the nuclear war occurs. But that could only be true if the future is
not
fixed as of 1994. So is there a way of reconciling both the fact that Terminators travel back in time from a post-Judgment Day future with the fact that the future is not fixed and the date of Judgment Day is ultimately changed?
There are two ways to look at this. One possibility is that there is a second temporal dimension in addition to the existing dimensions of space and time; we might call this dimension “meta-time.” Most philosophers doubt that there is anything like meta-time, but even if there were, our problems would be just beginning because we would need “meta-meta-time” to make sense of “meta-time,” and so on. I agree with these skeptical thinkers, but if there
were
such a thing as meta-time, then the story that unfolds in
T2
and
T3
would make a lot more sense.
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Let’s see why.
Let’s say that the
T2
timeline is one in which eternalism is true: the universe is a four-dimensional block in which all events, past, present, and future, are located. In addition to this block, we have meta-time, which is not a part of this block universe. At any moment in meta-time, we can ask the question “What does the four-dimensional block look like now?” Intriguingly, the answer to this question will vary depending on different meta-times.
Here is one way of making sense of what happens between the events of
T2
and
T3
. There is some meta-time, t
1
. At this moment, the four-dimensional universe is one in which the original T-101 arrives in 1984 and attempts to kill Sarah Connor. Ten years later, no Terminators arrive from the future, and in 1997 Judgment Day occurs so that in 2029, machines rule the world. If we consider 1994 within this block, we can see that the future is fixed. Since this is the eternalist’s universe, it’s true even in 1994 that Judgment Day will occur in 1997. In effect, 1997 exists as a future location on the block.
Now consider what happens when the Terminators travel back in time to 1994. They travel back to a 1994 that is located at a different meta-time, t
2
. In the new 1994 (relative to t
2
), quite different events unfold—Sarah escapes from the psychiatric hospital and decides to kill Dyson. Ultimately, what would have been Skynet is blown up. Relative to meta-time t
2,
then, the four-dimensional block looks different from 1994 onward: it is a world in which Judgment Day doesn’t occur in August 1997. The eternalist should be satisfied, since the future is fixed, but fixed
in a different way
. So in 1994 (relative to meta-time t
1
), Judgment Day does happen in 1997, and in 1994 (relative to meta-time t
2
), Judgment Day does not happen in 1997. Despite the problems with the idea of meta-time, it allows us to give an account of what happens in the
Terminator
timeline, an account that’s consistent with both Reese’s and Sarah’s sentiments in
T2
. At 1994 in the original meta-time, Judgment Day would have been in 1997. So when Sarah told the psychiatrist that he was already dead, she spoke the truth. Relative to that location in meta-time, her psychiatrist does die in the future. But Kyle is also right in his message to Sarah. While the future is fixed relative to a meta-time, the timeline as a whole can be different relative to different meta-times. So relative to different meta-times, what happens after 1994 can be quite different.
There is another possible explanation, though. Suppose that the
Terminator
universe is not a single four-dimensional block at all, but that it has a branching structure, like a tree’s roots. Whenever there is a point where different outcomes are possible, the universe branches, and each of those outcomes occurs, but on different branches. So, for instance, if I am rolling a six-sided die in a branching timeline, then the universe will split six times, and in each of those branches the die will come up with a different number on its face.
The branching idea gives us an alternative reconstruction of the events of
T2
and
T3
. Terminators travel back to 1994 from a future branch in which Judgment Day has occurred in 1997. But the location they travel back to is before 1997, so from the perspective of 1994, there are future branches on which Judgment Day occurs in 1997, branches in which it occurs at some other time, and branches on which it does not occur at all. The events on each of the branches are fixed.