My friend Frank Taylor was in town over the Thanksgiving holiday, having flown in from South Africa. With his wife Karen, Frank has spent the years since 2009 circumnavigating the globe aboard a 50-foot catamaran called Tahina, an adventure chronicled with spectacular photography on the Tahina Expedition blog. I highly recommend the site for anyone interested in travel and the sea, not to mention how high tech has transformed the ancient art of sailing. But when we spoke recently just before Frank returned to Africa, he had another kind of high tech in mind. Specifically, what had I thought about the film Interstellar?
I haven’t delayed my comments on the movie intentionally, but I was slow in getting to see it, missing the opportunity at the end of the Tennessee Valley Interstellar Workshop and then getting involved in recent activities including the One Earth New Horizons Message workshop at Stanford. I also wanted to read Kip Thorne’s The Science of Interstellar (Norton, 2014) and give the movie a second viewing. All that behind me, it’s time to explain why I was surprised by Interstellar. My expectations for Hollywood science fiction are always low, as I’ve found that today’s filmmaking wizardry all too often masks serious flaws in plot and character.
I can find problems in Interstellar as well, as many reviewers have, but I think this is an important movie whose mistakes aren’t significant compared to what it accomplishes. Interstellar is a movie that will baffle a large part of its audience, the movie-going public far more comfortable with battles in space and sleek starships like the Enterprise. This is not an audience that will easily follow the twists and turns through time and space that Christopher Nolan has created. But Nolan’s attention to detail, his partnership with Thorne, and his insistence on scientific plausibility wherever possible will get through to an important subset.
I’m talking about younger people with an interest in science for whom the movie’s stunning visuals will impel them to learn how to untangle the plot. For the intellectually curious, Interstellar is a tandem creation, a movie/book duality where each plays off the other — the motivated minority will want to immerse themselves in both. The film’s plot is demanding and operates at various degrees of believability, but there is a science puzzle to be untangled here, one to which Thorne’s book offers the key. When I was researching Centauri Dreams back in 2002-2004, I was surprised at how many scientists and aerospace engineers told me they had chosen their fields because of science fiction novels like Poul Anderson’s Tau Zero. This movie will have the same effect. In fact, I can think of no movie that is so likely to create careers in the sciences, particularly physics, than this one.
Let’s talk about why. Here I get into details and suppose I should say that there may be spoilers below for those who haven’t yet seen Interstellar, so proceed with caution. I could focus on various issues, from a worldwide blight to passage through a wormhole, but the film’s treatment of black holes is what I’ll use as my working material. The wormhole itself, out near Saturn’s orbit and an apparent way out for a desperate humanity, is richly described in Thorne’s chapters, especially with regard to the special effects that bring it to life.
Our protagonist, Cooper, must learn which of three planets in an unusual system dominated by an enormous black hole called Gargantua is most suited for humans. When he and his team need to get to one of these, Miller’s Planet, from their parking orbit near the black hole, they have to produce huge velocity changes in the range of 100,000 kilometers per second. Thorne goes through the physics of this, including the bizarre time distortion on a world so close to a black hole. The upshot is that a gravitational slingshot maneuver must be performed. The movie skims over the matter quickly, but Cooper does discuss how this must have been done later, when he talks about using a neutron star to decelerate. The neutron star is a bit of a fudge — it turns out it wouldn’t be big enough to force the needed maneuver, but an intermediate-mass black hole would do the trick. Thorne made this case to Nolan but the director stuck with the neutron star.
That’s a scientific error forced by Hollywood values. Thorne relates his objections to Nolan during the re-writing of the screenplay and goes on to explain what happened:
…he [Nolan] didn’t want to confuse his mass audience by having more than one black hole in the movie. One black hole, one wormhole, and also a neutron star, along with Interstellar’s other rich science, all to be absorbed in a fast-paced two hour film; that was all Chris thought he could get away with. Recognizing that strong gravitational slingshots are needed to navigate near Gargantua, Chris included one slingshot in Cooper’s dialog, at the price of using a scientifically implausible deflector: the neutron star instead of a black hole.
Interstellar is closer to three hours than two (Thorne was writing before the film was finalized), but does anything else about this bother you? I’m going to argue that the combination of Nolan’s movie and Thorne’s book — and the fruitful collaboration the two engaged in throughout — induces the kind of puzzle-solving ethos that will prompt many a young mind to dig deeper into the movie’s physics. Nolan made a choice with a mass audience in mind, but the framework of that choice is laid bare in Thorne’s book, which goes on to explain how careful Nolan was to stick to scientific plausibility where he felt that he could. Filmmaking is always a matter of compromise, but Nolan was surprisingly tough. Finding where Interstellar works and where it stretches science out of shape is itself a lesson in problem solving.
The point is, the director was thinking about these things within a framework that, in terms of its spectacular visuals, is meticulous about getting the larger details right. Think about the accretion disk around the black hole Gargantua. Here we’re seeing a magnetic field in the process of converting gravitational energy into heat and then light — the field, explains Thorne, provides the friction that slows the circumferential motion of gas in the disk even as the black hole’s gravity tries to speed up the infalling material, with kinetic energy being converted into heat and light along the way. But go to the projections of black hole accretion disks you’ll find on the Net or in technical publications and you’ll find Nolan’s depiction is far more spectacular. Another Hollywood-enforced choice?
No. What Nolan and Thorne added was the gravitational lensing of the disk by its own black hole, an effect explored through computer code developed for the film. While you would expect that portion of the disk behind the black hole to be out of sight, gravitational lensing produces two images of it, one above and the other below Gargantua. This is special effects wizard Eugénie van Tunzelmann’s work, carefully wrought to produce the nested effect Thorne describes:
Inside these primary images, we see thin secondary images of the disk, wrapping over and under the shadow, near the shadow’s edge. And if the picture were made much larger, you would see tertiary and higher-order images, closer and closer to the shadow.
Moreover, Gargantua’s distortion of spacetime distorts the disk images, pushing the perceived disk away from the shadow on one side and toward the shadow on the other, creating an effect that appears lopsided. Here again Nolan intervened in an attempt to avoid confusion, especially as the audience tried to work out the reason for the lopsidedness of the disk and the star patterns created near its edge. So for the purposes of the imagery, he slowed the spin of Gargantua to reduce the effect, just as van Tunzelmann removed the Doppler shift created by the disk’s motion, which would have created an even more lopsided and confusing effect.
What pleases me here is that these changes and their rationale are thoroughly explored in Kip Thorne’s book, which likewise offers those intrigued with such visualizations the opportunity to explore how they could be fine-tuned and rendered with greater accuracy. Given the Hollywood culture in which he operates, I think that Christopher Nolan produced a movie with as much scientific accuracy as he could get past his producers, given the imperative for ratings and box office sales.
Most people are going to be wowed by the visuals; some will be dismayed by the all but supernatural intervention of beings from a higher dimension who may be our descendants. But a few, the ones I’m focused on, are going to use the high points of this movie — its unapologetic call for exploration, its entanglement with science as a form of quest — to choose to learn more, and there is no more engaging a guide than Kip Thorne to show them the way. Thorne says he was moved by the underlying message of Interstellar that the universe can be viewed optimistically because our species is capable of choosing its future:
But doing so, controlling our own fate, requires that a large fraction of us understand and appreciate science: How it operates. What it teaches us about the universe, the Earth, and life. What it can achieve. What its limitations are, due to inadequate knowledge or technology. How those limitations may be overcome. How we transition from speculation to educated guess to truth. How extremely rare are revolutions in which our perceived truth changes, yet how very important.
Thirty years from now there will be working scientists who explain to interviewers how Interstellar, a movie flawed by occasional mawkishness (think of Amelia Brand’s regrettable lines about love being the fifth dimension), weighed down by what may be the ultimate deus ex machina (in the form of Cooper operating through the tesseract), and reactive to Hollywood’s relentless popular ethos, nonetheless captured their imagination so that they read a book (Thorne’s) that helped to launch them down a path whose end they could not imagine. I call that a fine result, and reiterate my surprise in finding a Hollywood blockbuster I can seriously recommend.