Rian Johnson first cast Joseph Gordon-Levitt in the quirky 2005 film noir project Brick he made for less than $500,000. Back then the director and star were Hollywood up-and-comers—an indie director and a former child star. What a difference a few years makes. The pair reunited for Looper, a $30 million sci-fi thriller where Gordon-Levitt plays a young Bruce Willis charged with killing his future self, in theaters Sept. 28—the biggest film of Johnson’s career to date. TIME sat down with the 38-year-old director to talk casting calls, dystopian inspirations and his agonizing writing process.
TIME: You’ve done smaller budget films in the past, but Looper puts you in the big leagues. Did you know that going in?
RIAN JOHNSON: I think I would probably lose my mind if I thought in those terms when I’m actually sitting in front of the word processor. I hope it does reach a big audience, but that’s such an abstract thing. Making the movie was still very similar to making Brick and The Brother’s Bloom. It felt like a group of friends getting together to make a movie. Even the fresh blood we brought—Bruce [Willis] and Emily [Blunt]—instantly felt like party of the gang.
But the idea for the film originated years ago.
I wrote it as short film I never ended up shooting a few years before we even made Brick—so 10 years ago. But then it really just sat in a drawer until I finished The Brother’s Bloom.
Did you always know you wanted Joseph Gordon-Levitt as your leading man?
I was writing it for Joe. Largely just because we’ve stayed really good friends since we made Brick together, and I just wanted to work with my friend. I knew the part was going to require this big transformation and that’s something that Joe really loves doing, so for a lot of different reasons it made sense.
Then you cast Bruce Willis?
Bruce was like at the top of the list. I just looked at the list, and I was like, ‘oh my god, Bruce Willis.’ We said ‘let’s offer it to him but he’ll never say yes. But let’s try.’ We never thought he’d say yes.
(MORE: Stephanie Abrahams talks to Joseph Gordon-Levitt about becoming Bruce Willis)
Like many viewers, I didn’t notice the prosthetics Gordon-Levitt wears to look like Willis. How did you pull that off?
[Looper special makeup effects artist] Kazuhiro Tsuji is a wizard. But at first he looked at pictures of Joe and Bruce next to each other and he explained why it was impossible to make Joe look like a younger Bruce. He didn’t want to do the job because their heads are different shapes, and their eyes are different widths apart. But eventually we pestered him to death. What he did is amazing.
Gordon-Levitt wasn’t the only actor to undergo some big appearance transformations.
We have to talk about Emily [Blunt]! I had no idea how she would pull off being an American Midwestern farm girl. I couldn’t imagine that, and that’s part of why I cast her—because it’s like ‘I know she’ll do it but I don’t know how.’ And she showed up blonde and tanned. Joe is the transformation, the physical transformation, everyone’s talking about, but she had just as big a transformation. She looked like a different person on set.
Her son in the film, played by Pierce Gagnon, is so creepy.
Oh my god, Pierce. Looking back I’m kind of terrified that I hinged the success of the backend of the movie on finding someone like Pierce. It’s really rare to find a kid who can do what he does. He would do three-page dialogue scenes with Emily and Joe and hold his own against them all the way through.
Joe started acting around that same age. Joe was six when he started acting. Pierce was five when we made the movie.
(MORE: The Hottest Sci-Fi Moms)
So Pierce is going to be the next Joseph Gordon-Levitt?
He’ll definitely surpass Joe!
How did you conceive your dystopian vision of the future?
It’s so easy these days to make these far-out futurescapes that look incredible but aren’t really grounded. Our very talented effects guys would send us these digital plates of the city, and they would look awesome but they would be too shiny and too out there. As a sci-fi geek, it took a lot of discipline to say, ‘well that looks really cool, but let’s pull that way back. Let’s look at the original plate. Let’s make it closer to the original buildings.’ We created a near dystopian future.
What were your influences?
It’s some Children of Men. There’s a little Bladerunner in there. I like when you’re doing a genre piece and you look outside the genre for influences. In that first part—in the city—I watched a lot of French new wave films to see the anarchy of these young people’s world and that feel of a devil main character. And then the back half of the movie we owe more to the films Witness or Shane than we do any sci-fi film. That’s what sci-fi always invites. It’s a genre that demands to be mixed with something else. And in many cases, the more odd the mixture, the more interesting the final product.
You’ve said that Looper isn’t really a time travel movie. What’s the central issue then?
You have to have something bigger than time travel that’s worth asking an audience to sit in the dark for two hours. And the power of a parent’s love really was the thing that set everything off. I realized that this weird little sci-fi concept could amplify that theme and be a conduit for it. I worked backwards from the end and planned the entire movie from there.
What’s next for you?
Unfortunately I don’t have a short sitting in a drawer I can pull out this time. I’m just carrying around a notebook and just scribbling down ideas. I need to get faster at writing. I’m just so slow.