"But black holes, as the name suggests, are murder on light. 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 traveling along straight paths,' says Eugénie von Tunzelmann, a CG supervisor at Double Negative. This was a whole other kind of physics. 'We had to write a completely new renderer,' she says."
"Von Tunzelmann tried a tricky demo. She generated a flat, multicolored ring—a stand-in for the accretion disk—and positioned it around their spinning black hole. Something very, very weird happened. 'We found that warping space around the black hole also warps the accretion disk,' Franklin says. 'So rather than looking like Saturn's rings around a black sphere, the light creates this extraordinary halo.'"
"That's what led (Kip) Thorne to his 'why, of course' moment when he first saw the final effect. The Double Negative team thought it must be a bug in the renderer. But Thorne realized that they had correctly modeled a phenomenon inherent in the math he'd supplied."
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How Building a Black Hole for Interstellar Led to an Amazing Scientific Discovery | WIRED
Kip Thorne looks into the black hole he helped create and thinks, “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. (That’s gravity for you; relativity is superweird.) In theory it was once a star, but instead of fading or exploding, it collapsed like a failed soufflé into a tiny point of …