What Does Wind Really Look Like?

Everybody talks about the weather, but James O'Brien is often rendered speechless by it. He's spent hours watching how snow forms drifts around buildings and how mud moves when someone steps in it. O'Brien, 34, is an assistant professor of computer science at the University of California, Berkeley, and one of the world's top experts on how to make computers simulate complex physical systems--such as waves, snowdrifts, viscoelastic fluids (goopy stuff, like mud) and (his favorite) explosions. His work lends a layer of reality to computer games and film animation in which wind, rain and other elements are driven by computer codes called physics engines. His algorithms are used in some PlayStation 2 software and at Pixar.

O'Brien's passion began when he was a Georgia Tech graduate student specializing in medical scans. Over drinks, friends told him they were creating a computer simulation of a man diving into a pool. "They said the water would be ridiculously hard to get right," O'Brien says. But O'Brien thought it was simply a matter of doing the math.

Or getting enough of the math right to fool the eye. Because computers don't have enough horsepower yet to simulate, say, every flake of snow in a drift, academics like O'Brien attempt to figure out how much we need to see to believe a scene is real. That's appreciated by animators and video-game artists who want simulations that look good but don't take a weekend to run. (It can take hours of computer time to generate one second of animation, but video-game players want things to happen in real time.) O'Brien's programs have helped some animations run 30,000 times faster. But he still isn't satisfied. He's developing simulation tools that are easier to use; someday, he hopes, anyone with a computer will be able to create special effects. --By Chris Taylor