HERE is one to ponder.

Rian Johnson, the writer-director of new time travel movie Looper, is in Los Angeles. It is 10am in the Golden State. His interviewer is in Glasgow, where it is 6pm. Are we talking in my past, in his future or are we both indisputably in the present?

If such conundrums delight your inner HG Wells fan, then Johnson's science-fiction actioner is for you. Set in 2044, Looper stars Joseph Gordon-Levitt as Joe, a hitman, or "looper", for the Mob. Joe's victims are no ordinary bods, but people sent back from the future. The "whacking" is still the same, but now science is involved. Just to make things more interesting, Joe's next client is his older self, played by Bruce Willis.

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Variously dubbed this year's Matrix or Inception's baby brother, Looper will confirm the helmer of Brick (2005) and The Brothers Bloom (2010) as a director of ultra-stylish, smarter-than-average blockbusters. But despite being a self-confessed "time travel nerd", Johnson has no desire to try it himself.

"I don't know if I would trust myself to go back. I've seen too many time travel movies, I know that's never a good idea. I can only mess everything up. Especially because right now I'm very happy with where I'm at, I'm getting to make movies for a living. I'd be afraid I'd say the wrong thing to the wrong person and come back here and find myself living under a bridge."

He came up with the idea for Looper 10 years ago. Unsurprisingly, he was going through a Philip K Dick reading frenzy at the time. After The Brothers Bloom was released, Johnson retrieved the idea from his hard drive (as he points out, in the digital age scripts don't languish in drawers any more).

His first and only choice for Joe was Gordon-Levitt, previously his leading man in Brick. Not only did the actor have to convince as a killer, he had to convince as the younger version of his future self, despite looking nothing like Willis.

"I knew it was going to be a real transformation," says Johnson. "That's what Joe thrives on, what he's really good at. He's got that character actor spirit."

For the rest, Gordon-Levitt had to rely on make-up, contact lenses to turn his brown eyes blue and his acting skills. "He got there just by watching a bunch of Bruce Willis movies, and he put the audio from the movies on his iPod and listened to them over and over. Bruce also recorded Joe's voiceover lines and sent him the recording so Joe could hear how he would say it."

Willis said yes to the film immediately, much to Johnson's surprise since the part is several universes away from the usual Hollywood action man fare. "Without giving anything away, the movie, and in particular his character, goes to some very dark places. He didn't put any resistance up to that, quite the opposite."

Once on the set, the Die Hard star, like the rest of the cast and crew, had a job just keeping up with a story that has more turns than a Waltzer ride. "I think we all had our thinking caps on," laughs Johnson.

Joining Gordon-Levitt and Willis is Emily Blunt. Like Gordon-Levitt, she had to undergo a transformation, morphing from the pukka English star of The Devil Wears Prada and The Young Victoria to a midwest farmer. "I knew she could pull it off but I didn't know how," says Johnson. Blunt duly listened to a lot of Chris Cooper, the Missouri-born star of Adaptation and American Beauty, dyed her hair blonde and acquired that tough, outdoorsy, sun-baked look.

Filming took place in Louisiana, and in particular New Orleans. Given that city's troubles, one might have expected Johnson did not have to do much to make it look like a dystopian city of the future. Far from it, says the 38-year-old. There are areas that still show the effects of the catastrophic flooding, but there has been so much rebuilding the city is now in great shape. "It's a really vibrant, beautiful, alive city. It was way too beautiful – we had to do a lot of work to make it look run-down."

Brick was Johnson's debut and his breakthrough movie, winning a special jury prize at Sundance. Not a lot has changed since then, he says with some relief. He is still working with much of the same team, including his cousin, Nathan Johnson, who provides the music for the films, and cinematographer Steve Yedlin. Johnson and Yedlin met at the University of Southern California School of Cinematic Arts. "It's kind of this little family that gets together every once in a while to make one of these movies," says Johnson.

Brick, a cross between a high school drama and a hard-boiled noir; and The Brothers Bloom, about a pair of globe-trotting con men, marked Johnson out as a director who liked to kick around ideas. His movies appear to contradict those who believe Hollywood is a film factory, churning out the same old, same old. Johnson, given his experience, is more generous. "The business sometimes gravitates towards the familiar just because it is a business, and it's better to put something on that's low-risk than high-risk."

But at the same time, he says, there are plenty of people out there who are looking for interesting material because they realise that is where the smart money is now.

"Audiences don't want the dull and familiar, [they] are very thirsty for stuff that engages them, that doesn't just dazzle them with huge special effects. When I see films that are able to pull off both spectacle and true engaging entertainment, like Inception for example, that's incredibly encouraging."

As if mastering space and time were not enough to be going on with, Johnson added to the complexity of the directing task on Looper by having a five-year-old in the cast. Young Pierce Gagnon, however, turned out to be a true team player.

"He would sit down and hold his own with Joe and Emily in three-page dialogue scenes. It was amazing to watch. Joe started as a kid actor around Pierce's age. Something he has always said is kids can act; adults have this notion that you have to trick a little kid into giving a performance but the truth is there are children who are actors, and great actors. I saw what he meant with Pierce.

"He was just like another actor on set. In between he was a healthy five-year-old, running around kicking everybody in the shins and asking what time lunch was, but when those cameras were on it was amazing to see this five-year-old who just can act."

Now with three features to his name, Johnson is musing on the next. "I'm chewing on a couple of things; it's still early days. They're both in the sci-fi world. I really enjoyed working in science fiction. It gives you a lot of cool opportunities."

Time travel again, by any chance? "No more time travel," he laughs. "It's too hard!"

Looper opens on September 28.