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Every once in a while, you find among all those assignments and readings, you have a
piece of work that you are actually quite proud of. I recently handed in a paper (two
weeks late) about time that falls into that category. As I plow through the rest of my
finals – wish me luck – I offer you a quick look into what I’ve learned in my course on
metaphysics.
Metaphysics, very bluntly, is a study of what is real outside of the human brain and what isn’t. One could argue that any number of things are merely human conventions. The existence of a God or creator, for example, has been up for debate for as long as there has been debate. Even the question of whether objects are real is up for constant debate in the field of metaphysics. Time just so happens to be up for review, too. As I dispense (or, better put, regurgitate) my knowledge of the metaphysics of time, you might realize that the way we think about time is much more complicated than a ticking clock (the mechanism of which is certainly complicated).
Exemplified in idioms like “Time flies!” or “Time never stops,” our prototypical concept of time is that time moves. It seems to move forward at a constant speed without pause.
Time cannot be stopped, not by a superhero or with the pause button on a remote. This seems straightforward. But it gets complicated when we investigate our concept of motion.
What does it mean for something to move? Like those math problems in grade school, we understand that objects move in space by a factor of time.
D (distance) = S (speed) x T (time)
When a train leaves the first station at an average speed of 100 miles per hour, it should arrive at the second station 400 miles away in 4 hours. How far would the train move in zero hours? Zero distance. Nothing moves in no time.
There comes a problem: if everything moves in relation to time and nothing in no time, how does time move? Our concept of motion is inherently tied to time. Time could not move on its own or in relation to itself, as that would betray what we just said: nothing moves in no time. If time does move, it would have to move in relation to some higher order of time, like hyper-time or meta-time. But if such a thing existed, that order of time itself would have to move in relation to an even higher order of time to meet our definition of motion. What might be called the flow theory of time seems to fall apart in this infinite regression.
With the flow theory set aside, there seem to be two options: time is more complicated, or it does not exist at all. To avoid hasty conclusions, there is another, more robust theory of time. Premised on the idea that time is a dimension like those of space, the space-time theory becomes much more convoluted than the much simpler flow theory. And while it accounts for motion better than the flow theory, the space-time theory has its own implications and issues.
One similarity between space and time that we see in the figure above is that objects have parts in both. Without digressing into the metaphysics of objects, we might say that objects in three dimensions have parts. A human, like the one (or many) pictured above, is made up of smaller parts like arms and legs. The same is true of objects in the fourth dimension. The human pictured above is one continuous fourth-dimensional object made up of many temporal parts. The whole fourth-dimensional object is, in other words, a sum of its temporal parts. With any part of that person in time removed – say, if we took out the birth of the person – that temporal object seems incomplete.
Another way in which time and space are similar is the reality of objects. Though we only experience the world from our position in space, we acknowledge that those other places across the Earth and universe are just as real as our place in the world. We do not need to see Tokyo with our own eyes to know that millions of people live there. Likewise, places in time exist just as much as the present. We might push back on this assertion: things in the past did exist, but they do not exist now. That might be true, but it does not mean that those objects are not real. When we say that an object did exist, we only mean to say that an object exists in the past which does not exist in the present.
This highlights a third similarity between time and space: the concepts of here and now. When we label a position “here,” we mean to say that we occupy that position in space. In the same way, we use the label “now” to indicate our position in time. “Here” and “now” are inherently subjective terms. When the weather forecast says there will be rain, but we go outside and say to ourselves, “There are no clouds,” we really mean to articulate that there are no clouds here and now. We do not mean to make a false assertion that clouds exist nowhere and at no time.
Though the space-time theory seems more robust than the flow theory, it has its own issues. There are still a few differences between time and space that raise questions.
One objection to the space-time theory stems from a quality seemingly unique to time: change. In the first three dimensions, objects often differ between their parts. A knife, for example, might be sharp at one point and dull at another. These variations across three-dimensional objects are just that – variations. But when a fourth-dimensional object varies, we consider such differences change. Variations along the fourth dimension are not as simple as variations. For instance, when we see a child whom we last saw as a baby, we do not find that their appearance has varied. We regard these differences fundamentally as change.
Perhaps our concept of change is really a convention. But this example of growth feeds into another objection: motion. If we saw that same child after another period of time and they happened to be a baby again, we would certainly find that this child had again changed (quite shockingly). But this does not happen; objects only move forward in time. In this way, time is fundamentally unlike the three dimensions of space. Objects are free to move up and down, left and right, forward and back. But in the fourth dimension, movement is restricted to only one direction.
Maybe this too is a matter of convention. Maybe we can only see things move forward in time because we are merely three-dimensional beings. These first two objections can be argued, whether through physics or semantics, but one last objection remains unsolved: causation. In the first three dimensions, an object can cause another object to move in any direction. A bowling ball can knock a pin forward, backward, up, down, left, or right. In time, an object in the present can even affect an object in the future. But an object in the future cannot affect an object in the future. This is a fundamental difference between time and space that seems hard to square.
But what if we square it anyway? One fun quirk of the space-time theory is that it opens the possibility of time travel. If time just flows forward, then that’s that. But if time is the fourth dimension, ontologically similar to the dimensions of space, there might be a way to navigate the other way.
If we could move backwards in time, and thus achieve backwards causation, what would happen? Backwards causation seems to create blatant contradictions. Stories like Back to the Future and “’– All You Zombies –‘“ entertain the most popular dilemma in time travel hypotheticals: causing one’s own birth. In Back to the Future, the main character nearly seduces his own mother, almost preventing her union with his father and thus removing him from reality. The main character of “’– All You Zombies –‘“ comes to realize that he is his own mother, father, and daughter through extensive time travel and one sex reassignment surgery.
Our favorite time travel stories seem to offer the same lesson: that time travel, while enticing and sometimes enlightening, would be much more trouble than its worth. Whether time is a convention or another dimension of our reality, it hardly seems achievable to move against the natural direction of time. But it’s just so entertaining to wonder if it were.
There’s plenty more to the metaphysics of time than I could cover. If you’re interested in the topic, or in metaphysics in general, I highly recommend my “textbook” for my metaphysics course, Riddles of Existence. This book is written so that anyone can drop in and enjoy. I don’t know whether time is a convention, whether it moves, or whether it’s the fourth dimension. One thing is for sure: I have to wake up at eight o’clock tomorrow.