There’s always a moment in time-travel pictures when somebody has to raise the issue of the paradoxes involved. Like, ferinstance, if you’re a dude from the future, why don’t you just remember what happened before and change your behavior accordingly?

Rian Johnson’s “Looper” has one of those scenes, in which a guy named Joe (Joseph Gordon-Levitt) and his come-from-the-future older self (Bruce Willis) sit opposite each other in a diner. The paradox thing comes up. And the Willis version shrugs it off: “If we start talking about it, we’re gonna be here all day.”

That’s one way to get around it — but what’s impressive about “Looper” is that it doesn’t leave it there. The older Joe actually does give an explanation, which makes sense in a sci-fi kind of way.

The movie’s like that. Every time you think it’s going to take the easy way out and settle for something conventional, it throws a curve.

We learn this early on, in a subplot about a rogue “looper” (Paul Dano) who suffers a disfiguring meltdown, the details of which we won’t go into here.

But what’s a looper? In this world, a looper is a hit man, just like Joe, who eliminates criminals sent back from the future. He’s well paid by his organized-crime boss (Jeff Daniels), and enjoys a hedonistic if morally empty lifestyle.

Loopers have a big clause in their contracts: At some point, they’ll be eliminating themselves — their older selves from the future. That’s necessary to close the loop on their activities.

Joe’s adventure with his future self is neatly worked out by writer-director Johnson, whose first film, “Brick” (which also starred Joseph Gordon-Levitt), marked him as an extremely clever talent.

The clipped, careful rhythm of the first few scenes in “Looper” lets you know right away you’re in confident hands.

As Willis enters the story, “Looper” introduces new plot ideas, some of which revolve around a Kansas farmer (Emily Blunt) and the little boy she says is her son. Johnson comes up with wonderful character touches to suggest things about people: Before we’ve gotten to know Blunt’s character, we see her sitting quietly on her porch, miming the action of lighting and smoking a cigarette. We’re not sure who this woman is, but we want to know more.

Johnson darkens his set-up in interesting ways as Willis’ intention becomes clear, and “Looper” doesn’t settle for a once-over-lightly treatment. Instead of going the mind-bending route, it actually makes its time-travel game as clear as possible, and then ponders the human consequences of what might happen.

Throw in the eccentric facial makeup used to make Gordon-Levitt look like Bruce Willis (and the younger actor’s approximation of Willis’ trademark smirk) and you’ve got a memorable experience. Like other aspects of “Looper,” the makeup seems like a stunt at first — and then it pays off in ways you didn’t anticipate.

“Looper” (3½ stars)

“Brick” director Rian Johnson reunites with star Joseph Gordon-Levitt for this strong time-travel picture, about a hit man whose older self (Bruce Willis) returns. The mission darkens as it goes along, and Johnson throws unexpected wrinkles into the story line: This movie is about human consequences more than mind-bending paradoxes. With Emily Blunt.

Rated: R for language, violence, nudity.

Showing: Alderwood Mall, Cinebarre, Everett Stadium, Galaxy Monroe, Marsyville, Meridian, Stanwood, Thornton Place, Woodinville, Cascade.