IF YOU'RE some astrophysicist nerd who's going to "Looper" to live-blog about credibility problems with its time-travel plot, please stay home.

Among the movie's many pleasures is its built-in disclaimer/manifesto, set forth by Bruce Willis: "I don't want to start talking about time travel. Because if we start talking about time travel, we're going to be here all day."

Hear, hear!

This not only smooths the way for the mind-bending, time-hopping story that supports "Looper," but provides a framework for all time-traveling movies going forward.

So, paraphrasing Tyler Durden, let's all agree that from now on, the No. 1 rule of time-travel movies is, don't talk about time travel.

And, where "Looper" is concerned, don't ask why Joseph Gordon-Levitt has such a messed-up face here. It all sorts itself out.

He plays Joe, a hit-man from the dystopian near future. His job is to stand at a prearranged location, wait for a hapless time-traveler to appear from the future, and assassinate him.

One day, something goes wrong - he misses a hit on his intended victim (Bruce Willis) and sets out in hot pursuit. Soon both men are embroiled in an across-time conspiracy - factions trying to find and kill a little boy who will grow up to be a powerful and ruthless dictator.

The boy may or may not be living in the care of Emily Blunt, a single mom trying to manage a farm and her increasingly hard-to-manage son.

Joe ends up there, instinctively moved to protect them from now-and-future threats, and the movie cheekily invokes/merges movie archetypes as various as "Shane" and "The Terminator."

Writer/director Rian Johnson's nerve and verve are the show here - despite the movie's downbeat view of the life-is-cheap future, it's a kick to watch, and makes a virtue of its bleakness by virtue of amusing performances.

Willis as a hard-boiled emissary from the future, Jeff Daniels (suddenly Hollywood's leading grouch) the crime boss of the post-apocalypse, Blunt as the best-looking woodchopper in the history of movies.

The movie even has a little meat on its bones, adding moral trap doors to the first-let's-kill-Hitler priorities of time-travel conjecture.

There's plenty to think about.

Just can't talk about it, or we'll be here all day.

Contact movie critic Gary Thompson at 215-854-5992 or thompsg@phillynews.com. Read his blog at philly.com/keepitreel.