By the time Christopher Nolan signed up to direct Interstellar and started rewriting its script, astrophysicist Kip Thorne had been working with Nolan’s brother, Jonathan (who goes by Jonah), on getting his ideas onto film for years. When Chris and Thorne met, they quickly found common ground: Thorne wanted science in the story, and Nolan wanted the story to emerge from science. So in Interstellar, time dilation—the passing of time at different rates for different observers—became an emotional obstacle between a father and his daughter. Quantum gravity, the reconciliation of relativity and quantum mechanics, became the plot’s central mystery. The visual effects team even collaborated with Thorne to make sure their depictions of a black hole were accurate as well as elegant.

But to make it all work, Nolan, who never really understood algebra, had to internalize the science to which Thorne has dedicated his life. That the two men ended up liking each other was just a bonus. Here, Nolan and Thorne describe their work together, what they think they’ve achieved, and how they found détente when the story sought to break the rules of physics.

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