Movie Magic Conjured by Science

The special effects in Toy Story, Harry Potter and other blockbusters would not be possible without the complex field of fluid dynamics.

The next time you take in a movie, you may be getting a lesson in cutting-edge physics without even knowing it. Hollywood has embraced the complex field of fluid dynamics, the study of how water, air, smoke and other fluids move, in a big way, allowing filmmakers to create realistic scenes of turbulent oceans and falling buildings -- not to mention the quirks of Jeff Bridges' face.

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"It used to be that the story was limited by the technology," said Doug Roble, creative director at Digital Domain, a Hollywood special effects studio. "Now we're getting to the point where there are no limits. If I want to have Mount Everest fall into the ocean and catch on fire, we can do that. And the audience will buy that it is happening."

Computer scientists like Roble are using new kinds of software programs that harness mathematical algorithms that describe chaotic scenes of nature. These same kinds of mathematical formulas can be used to describe and then animate the bending of steel girders, as seen when downtown Los Angeles collapses in last year's blockbuster "2012."

Instead of just drawing a steel girder from a building and pushing it around, Roble says mathematical equations now determine how the object will move on screen.

"In order to get the physics right, the mathematics is very stiff," Roble said. "So in order to simulate it accurately, you have to take extremely small time steps to move the simulation forward. If it's too fast, the simulation will explode, negative signs start appearing, and your simulation won't mimic reality."

Canadian computer scientist Robert Bridson wrote about this emerging field of physics and animation recently in the journal Science. Bridson's company Exotic Matter has a long list of Hollywood film projects, including recent "Harry Potter and the Half-Blood Prince," "Hellboy" and "Quantum of Solace." He's an expert of sorts in creating realistic smoke, water, fire, hair, skin and clothing.

"(Digital filmmaking) has a lot in common with foundational work with applied mathematics and computational physics," Bridson said from New Zealand, where he's working on the latest Tolkien film, "The Hobbit." "People will look at a phenomenon of interest and come up with equations to describe what they are seeing. A lot of that is now going on in film."

Bridson said creating realistic sea foam and ocean spray has become the latest challenge for math-based special effects designers. He notes a particular complex shots of a both a giant wave and the lion's rippling fur in the just-released fantasy film "Chronicles of Narnia: Voyage of the Dawn Treader" that made heavy use of new fluid dynamics-based programs.

What's been driving the marriage of math and movie-making is the rising expectations of film directors and the availability of cheap computing power needed to run the software. That means big special effects no longer equals big budgets.

"We will start seeing more low-budget independent types of shops producing extraordinary effects," Bridson said. "'District 9' cost $30 million. Compared to the budgets of what other science fiction films need, it was pretty cheap."

Using computer simulation of solid and fluid dynamics is both cheaper for the director and less dangerous for human actors, Bridson said.

Both Roble and Bridson say the next step for creative programmers is creating digital doubles for human actors. By using a fully animated digital character, a director will be able to redo difficult scenes without rebuilding a set or requiring dangerous stunts.

In the recent "Tron" sequel, filmmakers wanted to recreate actor Jeff Bridges' character to resemble what he looked like 30 years ago. Using new software, they mapped Bridges' current face with a set of points, then transferred it to images taken from Bridges circa 1982. The data was crunched using software that wasn't available a few years ago, Roble explained.

"The human face is extraordinarily tough," Roble said. "Right now, the research community is focused on muscles and skin."

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