Jim Sturgess follows his starring role in "Cloud Atlas" with another visionary film. "Upside Down," written and directed by Juan Solanas, is centered on two planets that are planted one on top of the other, with equal and opposite gravity. The rich live "up top" and the poor can be found "down below." The worlds above and below you appear upside down.

The film, opening Friday, follows a cross-planetary romance between Sturgess' Adam and Kirsten Dunst's Eden. We spoke with the 31-year-old British actor about it.

When you get a script like this, do you spend a lot of time trying to figure out the science of it, or do you focus on other things? I didn't think too much about the science of it. I kind of just took it as a fantasy. It just seemed like a really fun concept. I didn't want to worry about whether it was possible scientifically to exist like that.

What sort of questions did you have about it? What I couldn't really work out what kind of film it was -- whether it was set in the future, or whether it was really sci-fi, you know. It wasn't until Juan, the director, sent me a bunch of graphic designs of how he wanted it to look that it suddenly made sense to me.

Are you just inherently attracted to this sort of ambitious sci-fi? It's hard because I guess a lot of the kind of other films I had made, I mean like some of the great English films that I've made, have not been seen by such a bigger audience, so I guess people think that's more what I do. But I guess there is something about seeing something visually, or something that lives in a fantasy landscape, that is really exciting to me. But I wouldn't say that's all I was drawn to.

How did you determine the differences between the worlds, in terms of how someone from "down below" might have to adjust physically to "up top" and vice versa? It was something that I spoke to Juan about. And we made a decision quite quickly: Once he's up there there's not going to be any awkward movement, or anything scientific. We kept reminding ourselves that this is just a fairytale, and it should be a fairytale. If you start getting bogged down with the reality, you're going to lose the beauty of the fantasy, really.

Ultimately, movies don't get much more romantic than this. That was what was really exciting. The story is actually a really classic love story. It's the classic tale of forbidden love that we see in "West Side Story" or "Romeo and Juliet," that kind of thing. So it felt like a really familiar scenario put into a totally unfamiliar world. In "Romeo and Juliet," it's family that's pulling them apart. In "West Side Story," it's a gang-related issue. And in "Upside Down," it's the idea of gravity, which is kind of frightening.

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