“I’m not afraid of death. I am an old physicist. I’m afraid of time.” — Dr. Brand (Michael Caine)
Interstellar is director Christopher Nolan‘s most polarizing film, but there is little debate that it’s his most ambitious. Indeed, by the end of the film’s nearly three-hour run time, it becomes apparent that literally no movie has ever been larger in scope. This is not hyperbole: The plot hinges on the presence of a multiverse, a concept that has yet to be proven scientifically but is certainly perfectly plausible — and I would argue pretty likely to exist in reality. After all, the universe has never made one of anything — not one planet, not one star, not one galaxy — so why would there even be one of itself? That’s hardly a philosophical stretch.
Many films have skirted around the themes and science explored in Interstellar, but none have had such advanced scientific theory woven into the plot so directly and completely. For example, we have seen countless movies use time travel. Usually it’s just a gimmick, and often there isn’t even an attempt at legitimately explaining it — it’s such a common conceit that we just accept the existence of time machines and the like and say, “Hey, it’s a movie.” (Case in point: the existence of not one but two Hot Tub Time Machine movies.) Here’s the thing though: In order for time travel to be possible, it has to occur the way it does in Interstellar: with the existence of a multiverse, and with beings in a universe other than our own — that has more dimensions in it than ours does — facilitating it.
I see I’m getting ahead of myself. First, let’s back up and go over some more basic physics. In our universe, there are three spatial dimensions. Most people know that. Time is an additional dimension that allows for motion within these three spatial dimensions to occur. (Really, that’s the function of time: without it, nothing would move.) These dimensions — three spatial, one temporal — are fused together to create a four-dimensional continuum of spacetime. Time itself, of course, is not spatial — in our universe, anyway. However, it would be spatial if we could move backward and forward through it, but we can’t: we are forever prisoners of the present, moving forward in one direction from the past to the future.
Why would time be spatial if we could travel backward or forward at will? Think about it: in our current spatial dimensions, you can move left or right, up or down, in or out. This is a bit abstract, but to be able to move forward or backward in time at will — and access what has happened or what will happen — is to move through the three spatial dimensions (as a whole) in either direction exactly the same way everyone can already move through the three spatial dimensions individually. If time is spatial in this fashion, then it would exist in a five-dimensional continuum of spacetime. The fifth dimension would be the equivalent of what time is in our universe’s four-dimensional continuum of spacetime: it would enable motion to occur within the four spatial dimensions.
Are higher dimensions possible? Sure. In fact, a staggering 11 dimensions are thought to be possible. What causes “extra” dimensions to appear is the presence of extreme gravity. Any object with mass has gravity. The stronger the gravity (i.e., the more massive the object), the greater the amount of warping of spacetime surrounding that object. Hence why the farther inside an object’s gravitational well you travel, the slower time passes relative to someone who is not inside that gravitational well. As an aside, this scenario actually occurs in our everyday lives: the GPS satellites orbiting the Earth are farther outside the Earth’s gravitational well than our smartphones are here on the Earth’s surface. Since time passes faster for the clocks on the GPS satellites, time is automatically corrected to compensate for this slippage when we look at our phones so that it aligns with the rate at which time passes on the Earth’s surface.
Since most of us never leave the Earth’s surface, the concept of time being relative is not just unnatural to us, our brains scream that it’s insane. I don’t know about everyone else, but I find physics to be so abstract that, broadly speaking, I find it harder than any other subject to understand. The science tackled in Interstellar is far more ambitious than any other film or work of science fiction I am aware of has ever attempted to approach, but I didn’t find it to be beyond my intellectual capacity. I think the film does a sufficient job of explaining the science so that the plot can be understood. However, I was a bit perplexed when I saw that many of the critics who did not enjoy the movie leveled criticisms of it based on an incorrect reading of events. For example, these clowns accuse Interstellar of falling into the “bootstrap paradox” trap (i.e., the plot creates an infinite cause-and-effect loop), when it actually doesn’t.
If you have seen the film, you will of course remember that Cooper (Matthew McConaughey) leaves Earth and, some two hours later, finds himself in a tesseract (higher-dimensional space where time is represented spatially) that allows him to communicate with his daughter Murph (Jessica Chastain) at various points in her life (and his own). Now, on the surface this does seem quite paradoxical: he sends himself back in time to arrange for the events to occur that brought him to the point where he is now. But he does not create this loop; these events have always happened this way, as astrophysicist Neil deGrasse Tyson explains:
In a higher dimension, you can step back and look at your entire timeline and access it no differently from how you just walk around in a room. So the question, ‘Can you go back in time to change something?’ That’s not even the right question.
Once you see your entire timeline, you are always being born. You are always dying. You are always in school. You are always asleep. You are always brushing your teeth. These things are always happening and you just access them at will.
So in the tesseract, he’s not changing the past. That always happened. We saw it happen. Jessica Chastain as a child saw the books come out. It’s a mystery why. We find out why: because her father does go into space, does go into the black hole, does access the tesseract, to try to tell him to not go.
But here’s the weird part: he did go. He had to go. Otherwise, he couldn’t be telling her that he shouldn’t go. So think about this: If she did interpret his signals correctly and managed to prevent him from going, then he never would have given her the signals in the first place to tell him to not go. So that entire series of events had to unfold exactly as portrayed.
And so you’re wrong to think that you’re going to go back and change something in a timeline that is already there. So yeah, it can make your brain hurt because we are prisoners in our own four dimensions and in higher dimensions really cool stuff can happen, as portrayed in the film.
So there you have it: the time travel in Interstellar does not fall prey to the bootstrap paradox. In order for time travel to actually occur in our universe, beings with access to five-dimensional spacetime (i.e., from a universe with five-dimensional spacetime) need to set in motion the events that occur within our universe’s four-dimensional spacetime. However, for the object/human to actually travel backward or forward in time, access to five-dimensional spacetime would be needed — hence the tesseract. How do they place the tesseract there? Keep in mind, the higher-dimensional beings of the film do not exist (or at least originate from) within our universe. Instead, they are in a different universe — one that has an extra dimension in its spacetime fabric. Because of this, they have power over spacetime that we do not possess — what Cooper experiences in the tesseract is a simplified version of what is normal for them.
Let me explain why a multiverse not only isn’t a stretch philosophically (i.e., the universe has never made one of anything, so why would there only be one of itself), but it’s likely quite plausible scientifically. Everyone is familiar with the Big Bang — the birth of our universe. Long story short: all of the universe’s matter and energy was confined within a tiny dot, and then it exploded. That tiny dot is commonly understood to have been a gravitational singularity — the very bottom of a massive gravitational well (shaped like a cone with a point/singularity at the end). Black holes likewise have a gravitational singularity, which is integral to the plot of the film, of course. Maybe you see where I am going with this: black holes, it would seem, potentially give birth to other universes, sucking in matter and energy and funneling it into a singularity — until it explodes.
Can we prove that scientifically? No, because (like in the film) we currently cannot collect that kind of data and evidence — it lies beyond a black hole’s event horizon (the point at which gravity becomes so strong that nothing — not even light — can escape). But try this on for size: our universe may just be on the other side of a giant black hole. And if that’s the case, wouldn’t we want to know what is on the other side of that black hole? The five-dimensional beings in Interstellar apparently decided they wanted to know the answer to their own version of that question, which led them to our universe. The source of their desire to save us isn’t made clear, but hey, if a black hole in our universe created their universe, maybe they felt that by association they owed us one or something. Either way, since it’s kind of impossible to show a five-dimensional being on film, we can’t really expect the movie to explain that or show that.
As for how they got to our universe, there are some clues as to how that happened. Consider the presence of the wormhole — a tear in the fabric of spacetime that allows for two separate points in space to be folded on top of each other so that a great distance can be travelled in a much briefer period of time. If they have the power to do that, it would follow that they have the power to create a wormhole between our universe and theirs. If our universe is considered to be part of an even bigger “everything,” then it would certainly seem possible to travel between universes — dimensional differences be damned. As an aside, here’s something that I find interesting: frequently, those who believe in God insist that life’s events have been predetermined (by God, of course). This would therefore make God a five-dimensional being, shaping our lives and timelines — or, more precisely, having already shaped them — from outside our universe.
The difference between this idea of God and the five-dimensional beings in Interstellar is God’s supposed power to create our entire universe in the first place. Maybe someday we will see a science fiction story about a multiverse with God’s role in creating our universe explored from within that kind of framework. Of course, while this would be a more concrete conception of the God conceived by Western human civilization, it is still subject to infinite regress — who then created God and the multiverse? Such is the nature of contemplating the cosmos: if the universe were simpler, our brains probably would be simpler too, and as a result we still wouldn’t be able to understand what the hell we’re doing here. (The human condition is a real bitch, isn’t it?)
I have now used around two thousand words to unapologetically dive straight into the science of Interstellar with mostly only incidental references to the film’s characters and basically no references to the movie’s actual premise. I suppose that was unavoidable — only those who have already seen Interstellar would even bother to read something like this. And besides, I’m not sure a proper deep dive into this film is even possible without leading with the science — particularly since the reaction to Interstellar was so polarized and the conclusion was so widely misunderstood. However, let’s now go back to the beginning of the film and walk through some of the events now that there is more clarity (hopefully) about how and why these events occur.
The film opens in the not-too-distant future. The world is ravaged by global crop blight; the planet’s population has diminished as a result. Cooper, his 15-year-old son Tom (Timothée Chalamet), his 10-year-old daughter Murph (Mackenzie Foy), and father-in-law Donald (John Lithgow) live on a farm somewhere in Middle America. In this world of decay, they grow corn — at least until blight eventually comes for it as well. Cooper was once a NASA pilot, but with the country’s resources long since having dwindled, he’s just a farmer now. (Well, and a widower. His wife had a cyst in her brain and died, when in decades past it would have been detected by an MRI.) The blight has caused a second Dust Bowl, with dust storms forming from the topsoil of failed crops.
If the above seems like a movie that’s a world away from where it ends up, that’s because Interstellar began as two entirely different projects — one a script by Christopher Nolan, the other a script by his younger brother Jonathan. The film’s first act resembles the original film as conceived by Jonathan before Christopher took the directing reins from Steven Spielberg. (Spielberg was attached to the film while DreamWorks was still a part of Paramount; once DreamWorks moved to Disney, he had to leave the project.) Christopher used Jonathan’s existing Earth-based script as something of a foundation, and then merged it with another space-based script he had been working on alone. On paper, this sounds like a bad idea, but spending so much time on Earth gives the story a sense of weight and, well, gravity. (The first time I saw the film in the theater, I can remember thinking about half an hour in, “Man, we must still have a long way to go since we’re not even in space yet.”)
And that’s one of my favorite things about Interstellar: it’s a huge story with a long, fulfilling arc that’s grand in scale but at the same time is more intimately felt than any movie this size theoretically should be. It’s about saving the human race, but it’s also about a man saving a broken relationship with his daughter. I’m not sure I can think of another film that keeps both the big and the small in sharp focus like Interstellar does. “Man leaves family behind to save the world” is not a new premise, of course — and for that matter, neither is the premise “man saves broken relationship with his daughter.” But implied in that first premise is the limitation that the hero has no communication with the family he has left behind — he simply forges forward and his family has no real role to play in the adventure ahead. Interstellar turns this premise on its head, since not only is Murph key to saving the human race from extinction, but Cooper must find a way to reconnect with her to complete the mission.
The presence of the tesseract in the third act is, uh, not something you see in most movies, but what it enables from a storytelling standpoint is something that is even more unique. We see Murph, standing in her childhood bedroom for the first time in years, peering at the books on the wall. On the other side, in a black hole in another galaxy, Cooper frantically attempts to get her to solve the puzzle from behind the books. Simply from a plot structure standpoint, I’m not sure I have ever seen this before: the protagonist travels an unimaginable distance, yet the focus never shifts from how events that are happening light years away ultimately shape existence at home. Furthermore, the relationship between both Murph and Cooper — the two characters separated by an incredible distance — is always in the foreground. We have seen characters needing to heal their relationship in order to achieve an objective before, but not quite like this.
Interstellar is clearly a big, action-packed spectacle, but at its core is something considerably more human than any of Christopher Nolan’s other films. Saving the world is not a new theme in his movies (he did direct three Batman installments), but gone is the coldness and angst of his approach to Gotham and the veneer of fantasy inherent to the Caped Crusader. The concept of stretching time isn’t an entirely new theme for him either (who can forget the mind-bending effect of dreams within dreams in Inception), but the embedding of relativistic time dilation into the fibers of storytelling is something that was unimaginable before Interstellar. Also, while the film is clearly presented as an old fashioned race against time, Interstellar is utterly unique in how it forces its characters to treat time as a resource. Can Cooper make it back to Earth in time? And what does “in time” even mean? In time to see his daughter alive? In time to see any human being at all alive?