MU-5: The Hollywood Connection!

The sci-fi movie, Interstellar, has two exotic concepts of physics: wormholes and black holes. If you neither know nor care about what either of those things are, don’t worry: this still makes for interesting reading.

When Christopher Nolan made Interstellar, he had a problem: while physicists and sci-fi fans may know what wormholes and black holes are, how would he render it onscreen accurately? Willing suspension of disbelief or not, sci-fi fans would tear into his movie if the rendering were obviously wrong in any way.

(In case you don’t know, a “renderer” is a piece of software that draws stuff on screen. The term will be used repeatedly, so it’s good to know).

Nolan turned to Kip Thorne, a retired astrophysicist who has always wanted to popularize relativity to the layman, for help:
“So he (Paul Franklin, Nolan’s computer graphics man) asked Thorne to generate equations that would guide their effects software the way physics governs the real world...Thorne sent his answers to Franklin...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 spacetime.”

The next step was rendering a black hole:
“But black holes, as the name suggests, are murder on light.”
Since they couldn’t show/draw a black hole (it was black), it would have to be depicted by what effect it had on everything around/near it. This was a problem since existing rendering software assumes (reasonably) that light travels in straight lines. Sadly for Franklin, that’s not true around black holes. So they had to write a new renderer for the black hole. This was so mathematically intensive a task that:
“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.”

When they applied the new algorithm for objects around a black hole, here’s what the rendering software made it look like:
“Rather than looking like Saturn's rings around a black sphere, the light creates this extraordinary halo.”
This was so weird that the team felt there was a bug in the software!
“But Thorne realized that they had correctly modeled a phenomenon inherent in the math he'd supplied…Thorne thought, “Why of course. That’s what it would do.”
In other words, Thorne got something out of all this that he didn't expect: a scientific discovery!

To summarize, the maths of general relativity was used to create rendering software which then showed how something would appear, something even physicists hadn’t known until they saw it. Quantitative understanding can sometimes become qualitative understanding after all!

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