One of the problems with a story that depends on dimensions beyond space and time is that it has to be complex but not complicated. An audience has to pick up concepts that even ace astrophysicists have trouble metabolizing. Like the proverbial observer in the theory of relativity, your perspective affects what you perceive. That’s what happened to Kip Thorne and Christopher Nolan. As they hashed out the science of Interstellar, the scientist and the storyteller looked at the same truths and—at least for a while—saw very different things. Here’s what their trip down the rabbit hole felt like.
WIRED: Chris, where did Kip have to rein you in?
NOLAN: There was one thing. I was determined to have a character travel faster than the speed of light.
WIRED: Uh-oh.
NOLAN: I wanted to break the light barrier, as I called it. And Kip wasn’t having any of that. That went on for a couple of weeks.
THORNE: I gave him a document where I laid out the reasons it couldn’t work.1 We had a couple of conversations, and he backed down.
NOLAN: We had more than a couple of conversations. What he’s not telling you is, I finally managed to get my head around relativity. I don’t mean a full understanding of it. I mean a glimpse of a feeling, you know? Like when you’re trying to play an instrument and you happen to hit the right chord? So I said, “You know what? I agree. Nothing can travel faster than the speed of light.” And he goes, “Yeah, well, in localized regions it can’t,” or something. And I’m like, wait a second! Every rabbit hole has another rabbit hole at the bottom of it, and another rabbit hole.
“The thing I most wanted was that the film have real science embedded in it—a range of science, from well-established truths to speculative science.” —Kip Thorne Dan Winters
WIRED: He incepted you with relativity.
NOLAN: Oh, very much. I lost it pretty rapidly afterward. Jonah says that through working with Kip, he finally grasped relativity for a couple of weeks, and then the writers’ strike happened and he had to stop writing, and it was gone. I know exactly what he means. It’s like a little window opening up. That’s why the relationship between storytelling and the scientific method fascinates me. It wasn’t really about an intellectual understanding. It was a feeling of grasping something.
THORNE: You call it a feeling; I would call it an intuition. And this isn’t just for nonscientists. Yakov Borisovich Zel’dovich, one of the really great astrophysicists of the 20th century and a codesigner of the Russian hydrogen bomb, was a close friend of mine. He could not grasp how Hawking radiation comes out of black holes, even though he had given Stephen Hawking the key idea that underlies the concept in a conversation the three of us had. For about two years, he could not make it fit with his intuition. Then, one time I was in Moscow and I went over to his flat. He threw up his hands and said, “I understand! I give up. Hawking was right.” He finally understood it in an intuitive way.
WIRED: Is that different than understanding the math?
THORNE: Very different. The math was there. The math was straightforward. Well, let me take that back—those are two different things. The math was there, and the steps in the math were straightforward, but interpreting the math was not so clear. And how you use the math depends very heavily on this intuition. It’s a key part of the scientist’s arsenal, as it is for the storyteller’s arsenal.
WIRED: Where else did you have problems with what Chris was doing?
NOLAN: Well, time dilation.
THORNE: Chris wanted a planet with time dilation unbelievably greater than I have ever seen in physics, and I just didn’t think that was possible. And he said, basically, “I gotta have it.” I went home, slept on it, did a calculation, and found that if you have a black hole that spins rapidly enough, and a planet that is very close to the last stable circular orbit, you could get the time dilation he wanted. It just amazed me.
NOLAN: Our meetings never ended with definite answers. They ended with questions. As a true scientist, Kip questions everything.
THORNE: Well as a true scientist I have been proved wrong so many times that I’m very humble.
NOLAN: Even if the audience can’t grasp the science, my goal was to make them understand it emotionally and for it to be clear that there’s a consistency and a reality to what we’re presenting. We went back and forth about time a lot, because Kip felt that I had done certain things at the end of the film that were at odds with the rules we had talked about. Kip thought we were seeing it different ways, and the truth is we weren’t. And I kind of knew we weren’t. So we bounced it back and forth—
THORNE: Yeah, a whole sequence of telephone calls.
NOLAN: Well, I didn’t want it to be dismissed as wild speculation. I felt very strongly that what we had done with the climax of the movie, we’re basically taking—I hate to use the term, in a way—an artistic approach to the key visual element. We tried to construct a rigid geometrical idea, thinking about the work of Escher or any number of artists, and build a set that can demonstrate it. I came up with this idea of an array, a matrix representing all the information of a four-dimensional world in three dimensions, or a five-dimensional world in four, depending on where you count time. Eventually I was able to say to Kip, “I am not violating the rules.”
A model of how a black hole would warp light around it (minus an accretion disc), based on Thorne’s equations.
THORNE: I was very happy with the whole tesseract scene—once he explained it to me. There is a fascinating scene earlier in the movie in which Brand (Anne Hathaway) says that to five-dimensional creatures, time is like mountains and valleys. You can go forward in time like climbing a mountain. You can go backward in time like going into a valley. It’s beautifully worded. But how does that fit with Chris’ rule set that says nothing can physically go backward in time? That’s where I was struggling.
NOLAN: I explained that her dialogue is about analogy, it’s about perspective. It all comes back to Flatland , I think. If you’re a two-dimensional being you can’t see two dimensions. You can see one. If you’re three-dimensional you can observe that second dimension. To me, time is like that. We can’t see it. We can feel it, and we can act accordingly. But if you were a five-dimensional being looking at our world, you could observe time as a spatial dimension.
THORNE: This is where we were talking past each other. To me as a physicist there is time that flows in the fifth dimension, in the bulk, and there’s time that flows in the brane2—our reality. They’re intimately connected. But this whole business that Chris was getting at was if you live in the bulk and you’re looking at how time flows in the brane, you can go forward and backward in time just fine.
NOLAN: But you can’t enter the brane. And I was determined. He kept saying to me, “No, it’s fine, I’m not saying it’s impossible.” But I didn’t want to let him down. I didn’t want him to think I’d broken my rule set.
THORNE: He was sure we agreed. I was sure we disagreed.
NOLAN: The geometry we constructed is an honest attempt to explain to the audience that from a higher dimension our world would look very, very different. It’s an impossible task, but the attempt was tremendous fun. I wanted to be sure Kip knew we hadn’t just said, “Oh, here’s the crazy bit.”
THORNE: Oh, I never had any doubt about that. I just had a doubt whether or not what you were doing fit with general relativity in five dimensions.
NOLAN: In a way, the tesseract3 is an analogy. Early in the film we talk about wormholes using a sheet of paper to represent the universe, and you can fold it over. But that piece of paper is representing three dimensions. You suppress the third to make it easier to understand.
WIRED: Like using two surfaces connected by a tube to diagram a wormhole, or a mass warping a sheet to represent gravity. The two-dimensional sheets stand in for three dimensions.
NOLAN: Right, you’re not moving on the surface. You’re moving in the surface. You suppress one dimension to represent what you’re talking about. As Kip and I talked about the wormhole, I finally understood that it’s a four-dimensional hole in three-dimensional space. And since a three-dimensional hole in two-dimensional space would appear as a circle, a four-dimensional hole would look to us like a sphere. That’s why I put it in the film. It changed everything about my ability to understand dimensionality.
WIRED: But how do you get something like that across to an audience?
NOLAN: I know how to do that because of the way photographic perspective works, which is essentially two-dimensional, and the way eyes work, which is also two-dimensional. Because of diminishing perspective, because things look smaller when they’re farther away, it’s actually pretty damn simple to go, “OK, we jump into this sphere, and then there’s a smaller sphere, and then it grows and we jump into that one.” The idea that the spheres at either end of a wormhole would be the same size? Photographically that’s no problem. We filmmakers deal with that kind of thing all the time.
WIRED: Fundamentally, film always flattens a three-dimensional world onto a surface. It’s not just metaphor.
NOLAN: That’s why I object to the term “3-D” for stereoscopic imaging, because movies are already three-dimensional. A photograph represents three dimensions in two. And then a strip of film adds time. That’s how you take time and you represent it physically: a reel of film running through a projector.
WIRED: Kip, did you interact with the actors too?
THORNE: I did. A couple of weeks before he started filming in Canada, I had an email from Matthew McConaughey. He was trying to wrap his head around the role of Cooper and the science. So we met at a boutique hotel in Beverly Hills where he had holed up for the weekend to try to—
NOLAN: With all his notes!
THORNE: Right, he’d cleared all the furniture out except for a love seat and a coffee table, and he had 12- by 18-inch sheets of paper all over the floor and on the table with notes all over them, each one dealing with a particular science issue or, I suppose, character issue. He would pull up a sheet and ask questions and write notes. Then he’d pull up another one. It was a wonderful conversation. And then I had a phone conversation with Anne Hathaway for about an hour and a half. She began by saying, “I’m a bit of a physics geek.”
NOLAN: Oh, she loves science. She was very excited to meet Kip.
THORNE: She had questions like “Are there any experimental tests for quantum gravity?” Her questions, you’d expect them from a science geek who spent the last three years reading physics. Maybe. If they were really on top of their game.
NOLAN: She loves science. Same with Michael Caine. He was super-excited to meet Kip. He took a picture with him. I’ve never seen Michael do that.
THORNE: The first assistant director came to me and said, “Michael Caine would like to have his photograph taken with you. Is that OK?” My jaw dropped.
NOLAN: The thing with good actors is, you don’t know what they’re getting from people. But there are two things going on with Kip’s involvement. One is, great actors can’t say lines that they don’t understand. Otherwise they can’t sell it. And then the other is, just by seeing somebody who has lived his life figuring these things out, they get some particular visual thing, whether it’s something you do, something you wear. It’s something that they absorb about what it’s like to devote your life to these principles.
THORNE: That’s the sense I had in my conversations with McConaughey and Hathaway. They were trying to wrap their heads around the science because they had to internalize it. With Caine it was more like he wanted to understand what it felt like to be a scientist.
NOLAN: I think one of the reasons is Michael doesn’t really have any science to discuss in the film.
WIRED: Chris, did you ever think, “Holy crap, I have a plot that involves both a wormhole and a black hole, and it’s really going to confuse people?”
NOLAN: No, I had a moment with Jonah’s draft where I went, “Holy crap, I’ve got six wormholes and five black holes.” I was like, guys, this is way too confusing. Kip had brilliant ideas using multiple black holes, but I just said, “No, we can do one black hole and we can do one wormhole, and that’s pushing it.”
THORNE: At one point in the story, a spacecraft that’s going at a quarter the speed of light has to slow down. I said the only way to do it is by a slingshot around a black hole. Chris said, “No, we can’t have a second black hole.”
NOLAN: Can’t do it.
THORNE: So I said, “OK, well, it’s a bit of a cheat, but you can use a neutron star.”
NOLAN: And we do.
THORNE: For me the thing I most wanted was that the film have real science embedded in it—a range of science, from well-established truths to speculative science. This is what we wound up with. And I’m just so pleased.
NOLAN: It all had to be done right for us to trust the bigger things we were doing. Early in Interstellar a spacecraft docks with a larger one. It was one line in the script. But it winds up being quite a lot of screen time because—well, there are two types of science fiction film. There’s the type where something like this would be scary and important for people doing it for the first time, and you go through that detail. And then there’s the kind of film where you go, “There’s the spaceship!” And then you cut to the characters sitting in fancy chairs, they hit the button, and we’re off! You have to clue the audience into which approach you’re taking. Then the bigger ideas, the more adventurous scientific ideas, start to gain credibility. Your audience starts to take them a bit more seriously.
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