Is time travel possible?
As a garden-variety ape with a wifi password and no physics, mathematics, nor philosophy degree, here is my disproportionately long opinion.
1. You’ve been a time traveller your whole life
The first, and fairly trite point to make is that traversing through time is not only possible, but seemingly mandatory—though only in what we discern as the forward direction. You’re doing it all the time, at a rate of 1 subjective-second to 1 Earth-second. If you’re sufficiently keen and wish to travel faster through time, you can gear up with some special relativity lore (passed down from father Albert), build yourself a suitably fast and comfy spaceship, then travel in a big loop at a significant fraction of the speed of light for a year—invoking the effects of time dilation. Or, if you’re wanting to save some money and effort, you could just cryogenicize yourself in hibernation mode and set a 100 year thaw alarm (warning: we might never learn how to successfully unfreeze you). Both tactics will drastically decrease the ratio of your subjective-second to Earth-second (your clock will tick much slower than Earth’s), and upon your eventual return to Earth time, you’ll find all those you love to be dead, and potentially a totalitarian AI regime that’s eager to rearrange your atoms into paper clips. Score.
I know, I know, I can hear your thoughts, as they, too, echo impatiently in my mind: “That’s not what I mean by time travel, you flappy-doodle!”
Word, let’s get to it.
2. Temporal paradoxes
Clearly, the primary interest in time travel is the ability to venture backwards through time. So what would that even mean?
First, let’s have some fun with the idea of travelling back in time, and then we can explore the real reason I’m sitting here writing all this nonsense; I think the question is rooted in a misunderstanding of reality.
Putting aside all physics skepticism, how might time travel logically work? Theoretical physicist and mathematician, Brian Greene, imagines jumping into a time machine and zooming off 5 years into the future to see if any breakthroughs have been made in his primary field of study: string theory. What he finds is mind blowing. Not only has a unified theory of everything been discovered, but when he asks who developed the theory, he finds out it was his mother—a person who knows nothing about physics in the time he just came from. Bewildered, he decides that he needs to go back to his timeline immediately to start teaching his mother everything he knows about physics, in order for this beautiful future to unfold; but then he has another idea. Why not just read the paper she wrote, then go back to his original timeline and tell her what to write? This seems much easier than to embark on an extensive, 5 year lecture series. So he does just that, and exactly as he witnessed during his jump into the future, his mother submits the theory and changes the world forever. But where did the physics insight come from? Who actually deserves credit for this paper? It’s definitely not Brian’s mom, since she just wrote what he told her to write, but it’s also not Brian, since he simply plagiarized his mother’s paper from the future. This is an informational paradox, and there are many other similar paradoxes, such as going back in time and killing your grandparents before they meet each other. How were you able to kill them, when your existence requires them not to have been killed?
One possible resolve to these time travelling paradoxes is that instead of travelling back in time, you’re actually travelling to a different parallel universe that’s nearly identical to your own. If that’s the case, then going back in time (to another parallel universe) and changing history as to deny the possibility of your birth just means you won’t be born in that universe, while your universe remains completely unaffected. When you eventually return from your sci-fi adventure to your original universe and time, nothing in your reality will have changed.
Seeing as we’re now 2 levels deep into speculation, I’m going to pull back the reins and course correct to what I see as a far more interesting direction.
It’s time to get to the juicy stuff.
3. Our Mathematical Universe
The way I see it, there’s a fundamental problem with the question—one which demonstrates a misconception of the nature of time. Max Tegmark’s paper, titled The Mathematical Universe, and his subsequent book, Our Mathematical Universe, instilled an insight in me that has profoundly influenced the way I think of the Universe. His core thesis is that the “unreasonable effectiveness of mathematics in the natural sciences”, as Nobel Laureate Eugene Wigner reflected upon, is not just a wacky coincidence. The reason mathematics has proven to be such an invaluable tool in understanding the properties and laws of the Universe, is because the Universe is in fact a mathematical structure. Yes, we live in a world with particles and forces, but every particle and every force is actually just an object of pure mathematics. Jesus, what a claim; let’s unpack that.
If you were to start zooming into any region of space (your hand, a raindrop, Jupiter’s rings, or “empty” space), you would eventually end up finding very peculiar particles in your field of view zipping about in an exceptionally disorientating manner. If you zoom in far enough with your imaginary microscope, say 10-18 meters by 10-18 meters (one trillionth of a trillionth of a meter), and freeze the frame at just the right moment, you will have before your eyes, an electron. Of course, the interaction of light required for you to see the electron will affect its position, and the amount of photons required to bounce off of the electron are too numerous for it to remain even remotely still. However, for sake of argument, imagine you have an image of a hazy dot in front of you: a single electron. But what is it? As far as we currently know, there are no subcomponents of an electron. It’s one of 17 to 54 fundamental particles in the Universe (depending on how you count… Feel free to dive down that rabbit hole) that don’t have any characteristics aside from their mathematical properties. Okay, but what does that mean? It means that the only way you can describe a fundamental particle of nature is through numbers. They all have a certain mass, spin, charge, and so on, that can only be described by mathematics. There is no other way to perfectly catalog these particles.
Now, if “A” is perfectly described by “B”, then “B” just is “A”. A truly perfect, all encompassing description of anything, is simply synonymous with whatever you’re describing. Take a flower, for example. No amount of linguistic elegance and hand waving is going to allow you to perfectly describe a flower. If you want to perfectly describe a certain flower to someone, you’ll simply have to make that exact flower and give it to them. The flower describes itself exactly. Therefore, if an electron and all other fundamental particles that make up the entire Universe are perfectly described by mathematics (which they are), then they are mathematics; they are a mathematical structure. By extension, since the Universe only consists of particles and forces (which are all purely mathematical structures), then the entire Universe must therefore be an unimaginably complex, colossal mathematical structure. Tegmark’s paper and book both provide a far more comprehensive narration of logic, but this is a heavily condensed version of the line of reasoning that made me start seriously considering the idea.
Now that we have a foundational understanding of the Universe as a mathematical structure, we can introduce time into the picture. In fact, it might be helpful to see how time affects the Universe if we first understand what it would be like without time. Whatever state a timeless universe is in, it will be like that forever. It doesn’t make any sense to think about how it got to be in its current state, because it’s always been like that. Therefore, we can think of any possible arrangement of particles frozen in time as a timeless universe. An example of such an arrangement is the precise position of every particle in our Universe riiiiight…. now: frozen forever. However you’re standing or sitting, whatever thought just crossed your mind, and whichever complex configuration all other particles are in throughout this grand cosmos are now as static as a rock. There is no process.
By adding time, you introduce change into a universe. Now there can be translation and rotation of particles. However, change is just a transition from one frozen, timeless state to another. Here’s a diagram to help visualize what I mean.
On the right in figure 1, we can see 5 specific snapshots of the moon orbiting the Earth at different moments in time: infinitesimally thin slices, or cross-sections, from the full picture on the left. On the left is the entire mathematical structure without specifically selecting any particular moment in time. The left image represents all of time and space as one static, mathematical structure. The word static is key here, as you can imagine that if you were trapped within the bounds of time (as you are), you would only ever be able to see individual snapshots of the Universe (the moment you were born, your first heartbreak, your 42nd time eating asparagus, etc.). However, from a perspective that’s outside of the Universe (the way in which you look at the left image on your screen), you can see the whole picture as it really is: a static, unchanging, mathematical structure. You could think of this as a ground vs aerial perspective.
If you were to zoom into the blue cylinder that is Earth in figure 1, you would see a densely packed web of particle positions through time—representing every particle on Earth throughout all time, much like the streaks of light you see in long-exposure photographs. Within that dense, noodly network, there exists an interweaving structure of particles that is your body, as seen in the middle and right images in figure 2. The rightmost image also includes your death, which we can visualize as a process of particles diverging away from their previously interconnected structure—which is just a nice way of describing your decomposing corpse.
With this model in mind, change, and therefore time, is an illusion. Just because you’re experiencing this moment right now, doesn’t mean that the instant you ate asparagus for the 17th time doesn’t also exist on equal terms. What we call the past and future, are simply other temporal slices from the forever existing, static, mathematical structure that is our Universe. Additionally, the fact that you’re experiencing this exact instant, says nothing about the importance of this particular moment in time; it just means that in this infinitesimally brief (thin) snapshot (slice), there is a life form on Earth that calls itself *insert your name here* and through some yet-to-be-discovered process, it is manifesting conscious experience. The conscious creature that you remember being 10 seconds ago always has, and always will exist. Right now, you are simply the momentary consciousness that is locked in this infinitely thin, timeless slice of the static, mathematical structure that is our Universe.
Okay, that was fairly dense. To help further develop an intuition of what I’m talking about, here’s an analogy that I’ve found to be quite useful:
Another way to think of the Universe, is as a flip book (see figure 5). As you flip each page, a similar, yet slightly different image is revealed, resulting in what feels like an evolving series of connected events. If you were to stop somewhere in the middle of the flip book, would you think that all previous pages no longer exist? Would you assume that there was something exceptionally special and unique about the page you stopped on? No, all the pages you passed are still there, and the page you’re currently on isn’t special at all. You had to stop at some page, and it just happened to be this one. This is the mathematical Universe diced neatly into frozen moments in time that always have and always will exist in their exact state.
4. Actually answering the question
Now that we have this new tool of temporal understanding, let’s return to the original question: is time travel possible?
Answers: (1) You’re confused; (2) no; (3) but also yes.
There are many topics that naturally demand answers from this world view that I’ve been describing, such as determinism, free will, the self, multiverse theory, Boltzmann brains, teleportation, matter-mind dualism, and so on. However, I have to stop somewhere eventually, or else my laundry will never get done. Since the view of the mathematical Universe hinges quite heavily upon some form of determinism, I’ll briefly address this as a bonus topic before bringing this post to a close.
Determinism is the idea that every event in the Universe has been predetermined due to the initial conditions of the big bang: cause and effect. No one thinking clearly will dispute the fact that the world is at least mostly deterministic, if not fully. Determinism is the reason science and all life on Earth has been so successful; if you understand how the world has previously worked, and you know some initial conditions, you can accurately predict what will happen in the future.
The one thing that seems to stand in the way of a fully deterministic universe is randomness. Some may think that free will is also a legitimate competing ideology, though free will is almost surely an illusion—one which plays the role of a damaging, cultural meme that many of us can’t seem to kick. I recommend watching this video if you’re confused on the matter, and with that, I’ll safely sidestep that topic.
Coming back to randomness, discoveries into the nature of quantum mechanics have sparked a whole host of confusion, which is why I tried hard to avoid the “Q” word, but ultimately felt it was necessary to touch upon. The bottom line (and a massively simplified explanation) is that we seem to live in a world where some predictions must break down to probability—even when we know all the initial conditions and physical laws at work. That is, for some experiments we can only be certain that 60% the time it will result in “A”, and 40% we will observe “B”—and this has nothing to do with how our observation of the experiment influences the experiment.
Thus, it seems like randomness has foiled the view of full determinism, since the Universe doesn’t know exactly what it’s going to do until the moment it does it. And the further forward in time you venture from your known initial conditions, the more reality will deviate from predictability, due to compounding quantum uncertainties. There is, however, a way to navigate around this deterministic blockage, but it requires taking a stance on understanding quantum mechanics conceptually—as opposed to mathematically—which is admittedly a dangerous and ill-advised road. With reservation and skepticism held closely, let’s briefly merge into the lane of the Many Worlds Interpretation (MWI) of quantum mechanics as a means of revealing a fully deterministic universe.
Instead of thinking about the experiment resulting in “A” 60% of the time, and “B” for the other 40%, the MWI proposes that both “A” and “B” happen. The theory is that whenever there is a probabilistic quantum phenomenon, the universe you are in diverges into two different parallel universes that before that moment, were identical. To use an example from Max Tegmark’s book, let’s look at the result of a man asking a woman out on a date from the standard view point many of us have (figure 7) and the view of the MWI (figure 8).
If the MWI is true, then our view of the static, mathematical Universe simply changes from 1 mathematical universe to an infinite number of separate, unchanging, mathematical structures that make up all the possible universes (governed by the same laws of physics). All of these parallel universes co-existing in the same higher dimensional space, called Hilbert space (see figure 9).
Therefore, instead of an event having a probabilistic result, what we’re actually measuring is whether we’re in universe “A” or universe “B”—where both of those parallel universes are static, deterministic, mathematical structures. Since both of the universes have always existed as unchanging mathematical structures, the problem that we’re facing with quantum uncertainty is not which of the two events occurred in the one and only Universe, but instead it’s determining which of the two universes we’re in. The fact that both universes have always existed in Hilbert space, means that they are fully deterministic, due to their unchanging, mathematical structure. Therefore, by understanding quantum mechanics through the lens of the MWI, we’re able to convert the randomness that previously foiled the possibility of a fully deterministic universe, into an infinite array of every single mathematically possible universe—all of which are static and deterministic.
6. Closing thoughts
I am fully aware that by walking through the door of determinism, I just opened a bunch of other strange and interesting doors, largely concerning the different possible levels of the multiverse and quantum mechanics. Again, my laundry will never get done if I attempt to explore all questions that branch off of this initial investigation.
In this post, I used the question of time travel as a vehicle to navigate through the view of the static, mathematical Universe, as I find it to be incredibly interesting and explanatory of the mysterious situation we find ourselves in. And though at times I’m sure I seemed to be swimming in confidence, I am by no means a fully committed subscriber to this theory. Even if I saw it as the most convincing explanation of our Universe, I must acknowledge how incredibly stupid I am, and the likelihood that I’m abundantly confused about almost everything one could be confused about.
On that note, I’m going to leave you with one of my favourite quotes from one of my favourite physicists:
“I have approximate answers and possible beliefs and different degrees of certainty about different things. But I’m not absolutely sure of anything, and there are many things I don’t know anything about, such as whether it means anything to ask why we’re here … I don’t feel frightened by not knowing things—by being lost in the mysterious Universe without having any purpose, which is the way it really is, as far as I can tell, possibly.”
– Richard Feynman