Subha Das Mollick
“Every great theory begins as a heresy and ends as a prejudice.”
Albert Einstein had once said, “Common sense is that layer of prejudices laid down in the mind prior to the age of eighteen.” Christopher Nolan’s Interstellar is commonsense defying, but it is intriguing enough for multiple viewing and a closer examination on the basis of known and accepted facts about the Universe.
Curiously, H.G Wells’ The Time Machine was published in 1895, where the protagonist, in his scientific lecture, speaks of time as the fourth dimension. Einstein published his Special Theory of Relativity, ten years later, in 1905. In his Special Theory of Relativity, he gave a scientific foundation to the idea of time as the fourth dimension. Following this, a spate of science fiction emerged on the idea of time travel and its consequences.
Interstellar is the latest in the genre of science fictions on time travel. Like The Time Machine, the first film of this genre, Interstellar too spells doom for the earth. However, instead of the climax, this is the starting point of the narrative. The film follows humanity’s last ditch effort to find a new habitable planet – after the earth is ravaged by environmental catastrophe. When former NASA pilot – turned corn farmer, Cooper, finds the co-ordinates to a top secret government project, he is brought in on the secret that the government has been working on – to send a crew to outer space in the hope of discovering a new refuge for humankind in a new galaxy. Cooper must leave his own family behind and journey into unknown regions of space. Thus begins the saga of space time travel of the protagonists, masterminded by a scientist Prof. Brand, who loves quoting poet Dylan Thomas, “Do not go gentle into that good night, old age should burn and rage at close of day. Rage, rage against the dying of the light.” In the film, the quote takes on multiple meanings – first, the scientist’s own old age and his urgency to solve an equation before he dies, the near end of human civilization on earth and humanity’s last ditch effort to save itself and finally, the struggle of a beam of light to escape the pull of the black hole.
Prof. Brand’s character has been modelled after an astrophysicist who has been the scientific consultant and an executive producer of Interstellar. The ‘science of Interstellar’, if one may call it that, has been developed through a close collaboration between the director Christopher Nolan and a scientist called Kip Thorne. Together they simulated hypothetical situations on the computer screen to test their plausibility. If Thorne saw truth in those simulations, Nolan saw beauty. Together they gave vent to their imagination in creating their own reality on screen.
Over the course of a couple months in early 2013, Thorne and Nolan delved into what the physicist calls “the warped side of the universe” – curved space time, holes in the fabric of reality, how gravity bends light. “The story is essentially of Chris,” Thorne says. “But the spirit of it, the goal of having a movie in which science is embedded in the fabric from the beginning, that was preserved.”
Playing with wormholes
In Interstellar, a wormhole essentially functions as a bridge connecting two points in space by taking advantage of imperceptible fourth dimensional space. Cooper and his co crew had to reach the stars that were really far away. Reaching even the nearest ones would take decades at speeds we humans have no idea how to attain. Back in 1983, when Carl Sagan (the American astronomer and cosmologist) needed a plausible solution to this problem for the story that would become the movie Contact, Thorne suggested the wormhole, a hypothetical tear in the universe connecting two distant points via dimensions beyond the four we experience as space and time. A wormhole was a natural choice for Interstellar too. As Thorne talked about the movie with Nolan, their discussions about the physical properties of wormholes led to an inevitable question for a filmmaker: How do you actually show one on screen?
When Einstein formulated his theories of relativity, he did not have the advantage of computer simulations. So he did thought experiments. Kip Thorne on the other hand, had the luxury of working with 30 computer programmers led by Paul Franklin. Franklin asked Thorne to generate equations that would guide their effects software the way physics governs the real world. They started with wormholes. If light around a wormhole wouldn’t behave classically – that is, travel in a straight line – what would it do? How could that be described mathematically?
Thorne sent his answers to Franklin in the form of heavily researched memos. Long pages, deeply sourced, and covered in equations, they were more like scientific journal articles than anything else. Franklin’s team wrote new rendering software based on these equations and spun up a wormhole. The result was extraordinary. It was like a crystal ball reflecting the universe, a spherical hole in space time. “Science fiction always wants to dress things up, like it’s never happy with the ordinary universe,” he says. “What we were getting out of the software was compelling straight off.”
Gargantua, the black hole
In the Interstellar narrative, on the other side of the wormhole, lies a giant black hole called Gargantua. Their success with the wormhole emboldened the computer graphics team to try the same approach with the black hole. But black holes, as the name suggests, are light guzzlers. Filmmakers often use a technique called ray tracing to render light and reflections in images. “But ray-tracing software makes the generally reasonable assumption that light is travelling along straight paths,” says Eugénie von Tunzelmann, a CG supervisor. This was a whole other kind of physics. “We had to write a completely new renderer,” she says. Some individual frames took up to 100 hours to render, the computation overtaxed by the bendy bits of distortion caused by an Einsteinian effect called gravitational lensing. In the end, the movie brushed up against 800 terabytes of data. “I thought we might cross the petabyte threshold on this one,” von Tunzelmann says.
For Kip Thorne, it was a chance to test his Hoop Conjecture through simulation. Thorne finally looked into the black hole he helped create and said, “Why, of course. That’s what it would do. This particular black hole is a simulation of unprecedented accuracy. It appears to spin at nearly the speed of light, dragging bits of the universe along with it.”
A planet orbiting the black hole?
In the film, Miller’s Planet orbits in a steady orbit on the peripheries of the black hole Gargantua. But how can any mass have a steady orbit in the vicinity of a black hole? Thorpe has confessed in an interview to Lee Billing, an editor at Scientific American covering space and physics:
“the problem seemed to be that no planet could endure the resulting gravitational forces. This was something that even I thought was impossible, intuitively, until I went and slept on it and did a few hours of calculations. I came to the conclusion that in fact it is possible. The black hole needs to be spinning very fast, but is possible for the spin to be fast enough for a planet in the necessarily close, stable, circular orbit to not be ripped apart. I can’t fault anyone for saying, “Hey, that’s not possible,” without first having the benefit of my book The Science of Interstellar! Unless it’s someone who is very deep into general relativity and who I would’ve expected to go do the calculations!”
Therefore, before dismissing Christopher Nolan’s idea of the Miller’s Planet, Thorpe took the trouble of doing the calculations and showing that stability is hypothetically possible. Because Miller’s Planet lies on an extreme curvature of space time, time on this planet is significantly slower. For every hour that this team spends on this planet, seven years pass back home on earth. In the film, Amelia, one of the crew members suggests that the effect of gravity on time has the unfortunate consequence of the team’s visit to Miller’s Planet. What they perceived as years of positive beacon from the planet, were actually mere minutes for the astronaut Miller, who was killed by the waves, moments after she landed.
But what are these huge waves that come after every hour on Miller’s Planet? Kim Thorpe explains that this planet is tidally locked, keeping the same face toward the black hole so that tidal forces don’t rip it apart. But it hasn’t been tidally locked for all that long, it was deposited in its orbit relatively recently, so it’s actually wobbling back and forth slightly relative to the tidal-locking position, and as a result huge tides are created in the ocean at the planet’s surface. And these tidal forces are so great that they create the huge waves you see in the film.
Having given satisfactory explanation to the stability of Miller’s Planet and to the waves, how would Thorne explain the fact that the accretion disk around Gargantua was energetic enough to provide light and heat for its orbiting planets, but not so hot and bright that it would bathe the astronauts in fatal x-rays and gamma rays? Thorpe explains in the interview with Lee Billing:
“This was a crucial detail that actually dovetailed with Chris’s filmmaking point of view. What Chris wanted was something that was visually impressive in optical wavelengths that the astronauts could see. So that’s what he got – something that glows in the optical but isn’t so hot that it pours off a lot of dangerous higher energy radiation. Let me say, though, that this particular quiescent and cool disk wouldn’t be in this state for an awfully long time. But, ha, all that the movie needed was a safe, bright environment around the black hole during the crew’s visit, and this disk meets that.”
The fifth dimension
So that is how the scientist and the film maker collaborated. Nolan came to Thorpe with specific requirements and Thorpe made calculations to see if the requirements were plausible. The computer modelling was accordingly adjusted to create the Universe of Interstellar. But this is a universe that abides by the laws of physics, how so ever obscure the laws be.
One such obscure concept is the concept of fifth dimension. In physics, the fifth dimension is a hypothetical extra dimension beyond the usual three spatial dimensions and one time dimension of Relativity. Physicists have speculated that the graviton, a particle thought to carry the force of gravity, may “leak” into the fifth or higher dimensions, which would explain how gravity is significantly weaker than the other three fundamental forces.
In 1993, the physicist Gerard ‘t Hooft put forward the holographic principle, which explains that the information about an extra dimension is visible as a curvature in a space time with one less dimension, just as a three-dimensional object can have a two-dimensional projection on a screen. Holograms, for example, are three-dimensional pictures placed on a two-dimensional surface, which gives the image a curvature when the observer moves. Similarly, in general relativity, the fourth dimension is manifested in observable three dimensions as the curvature path of a moving infinitesimal (test) particle. Hooft has speculated that the fifth dimension is really the space time fabric.
However, there are some portions in the film, for which the science is beyond the frontiers of our present knowledge. The issue of time travel is one. There has been a lot of research on whether the laws of physics permit travel back in time. Scientists have got interesting results but no firm answers. Thorpe informs Lee Billings, “In that area Chris made his own rule set, which we discussed at length when he described it to me early last year. And it’s a rule set for which I then could find a scientific rationale, but it was a rule set that was much less constrained by the laws of physics because we don’t understand the laws of physics in that domain yet!”
A non-negotiable demand
Even though Thorpe relented to the idea of time travel, which is so central to the narrative of the film, he did not relent to all of Nolan’s demands. Nolan wanted his astronauts to travel faster than light. But that was not to be. Thorpe recalls, “We’d always find some way to make things work together, though in this one instance of faster-than-light travel, I gave him a series of reasons why we were quite certain the laws of physics prevented it. We went back and forth for several hours on and off over two weeks about it, until he reached the point where he appreciated intuitively that the problems I was pointing out were insurmountable. Then he simply abandoned the idea of faster-than-light travel and moved in another direction.”
End result of the collaboration
In the end, Nolan got elegant images that advance the story. Thorne got a movie that teaches a mass audience some real, accurate science. But he also got something he didn’t expect: a scientific discovery. “This is our observational data,” he says of the movie’s visualizations. “That’s the way nature behaves. Period.”
In Thorne’s own words, “My interactions with Chris, and before him with his brother Jonah, the screenwriter, were really quite joyous. It was brainstorming in the best sense of the word, an artist and a scientist coming at a complex issue together, trying to generate ideas in the context of a story that is just coming into being, searching for interesting scientific ideas that would take the story in certain directions. Finding that common ground between two people of very different backgrounds – an artist that has a tremendous intuition into the universe and the laws of nature from self-education, but no real training, and me, a scientist with much more formal training – it was just a heck of a lot of fun.”
Compiled from the sources mentioned below: Robert Resnick, Introduction to Special Relativity, Wiley Student Edition
The author is the secretary of Bichitra Pathshala, an organization that promotes learning with moving images. She is also an associate director at iLEAD Institute, Kolkata. She can be reached at [email protected].