Directed by Christopher Nolan. Warner Brothers: 2014.

How did Interstellar come about?

Matthew McConaughey, Anne Hathaway and David Gyasi in Interstellar. Credit: Warner Bros. Entertainment/Paramount Pictures

I have long worked on black holes and, since the 1980s, wormholes — hypothetical tunnels in space that link distant regions of the Universe. About eight years ago, I and my friend Lynda Obst, a film producer, came up with a movie set on the 'warped side of the Universe' — black holes, wormholes, higher dimensions and beyond. It interested director Steven Spielberg, who brought in Jonathan 'Jonah' Nolan to write the screenplay. Steven dropped out and later Jonah's brother Christopher Nolan took over as director and final screenwriter. Chris and Jonah changed our story almost completely, but preserved the warped space-time and splendidly fulfilled our vision of a science-fiction movie with real science woven deeply in its fabric. In it, nothing violates well-established physical laws and all the wild speculations spring from science, not just the fertile mind of a screenwriter.

How hands-on were you during development?

Credit: Illustration by Jim Spencer

I met with Jonah and Chris every few weeks as they crafted the screenplay, brainstorming about the science. I worked on the visualization of black holes and wormholes with Oscar-winner Paul Franklin and his team at Double Negative Visual Effects in London.

Black holes do not emit light, so you visualize them through gravitational lensing — how they bend light from other objects. I took equations based on Einstein's general theory of relativity and created a description of a wormhole with three parameters: diameter, interior length and the degree of flare where the wormhole joins the external Universe. Paul's team used my equations to compute what a camera would see through the wormhole; Chris, perusing the images, chose the parameter values for Interstellar's wormhole.

The Science of Interstellar

  • Kip Thorne
W. W. Norton: 2014.

Did you learn anything new?

With computing power beyond what is normally used by physicists, and software designed to give rapidly changing images at IMAX resolution, we were able to see something never seen before. We simulated a fast-spinning black hole and a field of stars, and what we discovered is an amazingly complex, fingerprint-like pattern of starlight near the edge of the black hole's shadow, which comes from this gravitational lensing. There are regions where the stars look as if they are still, right next to others where the stars are swirling around. When we first saw hints of this, I thought we had done something wrong. We now think it is caused by a complex set of caustics (wrinkles) in the camera's 'past light cone' — not unlike the patterns on the bottom of a sunlit swimming pool. These wrap around the sky many times because the black hole's spin makes space whirl.

Was there any culture clash?

No, there was a full embrace of this melding of arts with science that extended to all four lead actors. Matthew McConaughey and Anne Hathaway came to me for in-depth discussions — they were trying to wrap their heads around the science. Michael Caine asked to have his photograph taken with me, and my jaw dropped. He told me his character was based on me and he wanted to talk about how a theoretical physicist thinks. Jessica Chastain asked for help with quantum equations. The nicest thing was working with artists who are brilliant, intellectually curious and from a background so different from my own.

Will interstellar travel ever be possible?

The nearest potentially habitable planet outside the Solar System is perhaps just under 12 light years (3.7 parsecs) away, orbiting the star τ Ceti. If you think of that distance as like going from New York to Perth, Australia, then the distance from Earth to the Moon would be about 7 centimetres. That gives you some sense of the challenge involved. I think humans will make that journey, but not in this century or the next, or maybe the one after that. It is too hard. For a science-fiction story, a wormhole created by an advanced civilization is the only way to do it in the next century, but it is unlikely that wormholes exist. You have to prop them open with 'negative energy' and it is unlikely that the laws of physics allow you to collect enough negative energy. But there is no proof that they can't exist.

What areas of physics currently excite you?

My passion is to understand the non-linear dynamics of warped space-time, and the ideal venue for this is black-hole collisions. There is a high probability that in the next several years we will detect gravitational waves — ripples in the fabric of space-time — generated by such collisions. A combination of computer simulations and gravitational-wave observations will really open our eyes about the behaviour of warped space and warped time when they are wildly dynamical. And who knows, maybe the next movie will involve colliding black holes. We will have to see!