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The director Christopher Nolan has spent a lot of time exploring the concept of time.

In 2000, his breakthrough movie, the thriller Memento, told the story — from end to beginning — of a man who'd lost his short-term memory.

As Nolan's films got bigger and more ambitious, he found different ways to manipulate time, in movies like Inception, Interstellar and Dunkirk.

His latest is a globe-trotting spy thriller called Tenet. In it, some of the characters and objects move backward in time, a process the movie calls "inversion," while others move forward.

"Time is the most cinematic of subjects," he tells All Things Considered."Before the movie camera came along, human beings had no way of seeing time backwards, slowed down, sped up."

In excerpts from the interview, Nolan discusses time — how to film a movie about it and why he is drawn repeatedly to it.

Interview Highlights

These have been edited for length and clarity.

Tenetis not about hopping to the past or the future, it's about time running backwards. Why did you want to make that the jumping-off point for the movie?

I think there's a really productive relationship between the medium and the physical reality of time and the idea of time that we all live in. So I've been dealing with this in my films for years and I had this visual notion of a bullet that's in a wall, being sucked out of the wall, and into the barrel of the gun it was fired from, and I put the image in Memento, my early film, as a metaphorical idea or a symbol of the structural notion of the film. But I always harbored this desire to create a story in which the characters would have to deal with that as a physical reality. And that eventually grew over the years into Tenet.

Did you have to train actors to throw a punch backwards or take a punch backwards, or do you just film it forwards and play it backwards?

No, we had to do everything four different ways, essentially. And so the actors are learning how to throw a punch backwards. They're also trying to work with the stunt team to determine what an inverted punch against somebody who's not inverted, what effect that has, because it's not just a straight backwards punch. And so you've got all of these different levels of complexity. And that took months of development. And then the actors coming in had to learn how to walk backwards, talk backwards. In [actor] Ken Branagh's case, talk backwards with a Russian accent.

What is it about you as a person that keeps being drawn to these questions of how we experience time?

What I like to say about my fascination with time is I've always lived in it and it's a glib response, but there's a truth to it. And as I get older — I turned 50 just before I released the film — as my kids get older, your sense of time changes.

In Interstellar, that's very directly presented. I think that kind of feeling that we all have as we get older of losing things and things slipping away and things moving ahead without us. And there's a tremendous sense, coming into the middle age of acceleration of time. And I think moving on to Tenet, the idea of looking at the world differently, this examination of, OK, why do we want to see a car chase in the film? Why do we want to see a plane crash? What's the excitement of that? How does that work? And trying to present it differently to the audience and for myself to look at it differently, turn it upside down, if you like, and time can do that for us.

When I got to the end of the film, I wasn't sure that I understood every moment ... and with a story this intricate, that sort of seems inevitable. Are you OK with that?

The interesting thing in movies is, you know, looking at the thriller genre in particular, you're not meant to understand every single aspect. You're meant to go on the journey, pass through the maze, understand the things you need to understand for the stakes of the scene you're in, and then you get to the end of the movie and you've been on a journey and you understand how you got there. That's the key.

The idea that you'd watch a large-scale studio blockbuster and come out feeling like maybe there are things I didn't understand that I should go back and take a look at or whatever. I think that's kind of fun. And as an audience member, I've always enjoyed movies that, if you want to see it a second time, you're going to see a different movie. You're going to see different layers in it. ... My job as a filmmaker is to make sure that the first time you see the movie, you are entertained and you are gripped and that, you can't lose sight of.

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