“Time travel has not yet been invented, but thirty years from now it will have been.” These words kick-start one of the grittiest science-­fiction films of all time, and it never lets up – not even after the credits roll.

“Looper,” skillfully written and directed by Rian Johnson, is about Joe (Bruce Willis), a looper (or assassin who works for big, organized crime syndicates in the future). In 2044, in an America where the economy has collapsed, the mob of the future illegally uses a technology that was banned the moment it was created: time travel.

Loopers are sent back in time to kill the desired targets and collect their pay (silver bullion). But they have a contract; when the mob wants to cut ties with anyone not in their tight-knit group, they send back the looper's loop (future self) to do what's called “closing your loop.” But when Joe's loop escapes, Joe's world is turned upside-down as reality begins to unravel around him.

Joseph Gordon-Levitt, who plays the younger Joe, does such a great job filling the shoes of a lost soul that if he's not nominated for an Oscar or Golden Globe, I'll be surprised. I've never seen a more captivating performance. Willis does a fantastic job as well, shifting the playing field and bringing the chaos in what is easily his best role since “12 Monkeys.” Emily Blunt is a surprise as Sara, a mysterious character who is introduced in the second half of the film but has a major impact on the story.

The writing is Oscar-worthy, as is the directing. The music by Nathan Johnson blends in with the intense action sequences and the emotional ­dialogue; it pays a great homage to Hans Zimmer and Harry Gregson-Williams. The visual effects are noteworthy as well (especially for such a below-average-budget film) but fall short of being as ground-­breaking and realistic as “Prometheus.”

Overall, “Looper” is an instant sci-fi classic and one of the best films of 2012 – a mix of “Blade Runner,” “The Departed,” and a dozen other classic sci-fi/action thrillers.

9.5/10 stars.

This film is rated R.