Will and Jaden Smith; Ryan Gosling and Jamie Lee Curtis. (WENN.COM)

The new time-travel thriller Looper stars Joseph Gordon-Levitt as the young version of a character played by Bruce Willis, despite the fact Gordon-Levitt resembles Bruce Willis about as much as he resembles Bruce Jenner. And given that nowadays Bruce Jenner looks like an old lady who's had too much plastic surgery, that's not good.

But through the magic of makeup and prosthetics, Gordon-Levitt in Looper is transformed into the spitting image of ... well, a guy who still doesn't look much like Bruce Willis, but with a fake nose and weird eyebrows.

We've seen this in sci-fi movies of late, with Zachary Quinto and Leonard Nimoy playing young and old versions of Spock in J.J. Abrams' Star Trek, and Josh Brolin doing a spot-on Tommy Lee Jones in Men in Black 3.

With a little help from time travel, cloning and magic, here are five more pairs of actors we'd like to see play the same character.

Arnold Schwarzenegger -- Chris Hemsworth

What do you mean there's a difference between Austrian and Australian? Oh. Well, buff Aussie Hemsworth (Thor) could probably fake an Austrian accent for any film that had him playing a young version of the newly returned-to-Hollywood Schwarzenegger.

The movie: Terminator: New Beginning. Arnie's too damn old to keep playing the ageless homicidal/heroic robot, so they need some way to introduce a new Terminator model that's the same but looks different. A passing of the plasma torch, if you will.

Sigourney Weaver -- Mary Elizabeth Winstead

Weaver and Winstead both have experience battling murderous xenomorphs -- Weaver in the Alien movies and Winstead in 2011's The Thing.

The movie: Weaver's Ellen Ripley has been cloned before (in Alien: Resurrection), so she can be cloned again. But this time the clone will be young, the way sci-fi clones are supposed to be, and played by Winstead. And they will appear together in Prometheus II. And it will make no sense. Just like the first movie.

Will Smith -- Jaden Smith

They've played father and son in The Pursuit of Happyness, but Jaden Smith could easily portray a younger version of his dad. Given the elder Smith's penchant for sci-fi flicks, we'll bet this actually happens someday.

The movie: With Josh Brolin doing a perfect Tommy Lee Jones impression in Men in Black 3, the time travel hook could be revisited in a future sequel, with Jaden Smith playing a young Agent J. Men in Black 5, maybe?

Jamie Lee Curtis -- Ryan Gosling

With their handsome features, winsome smiles, close-cropped hair and female sensitivities, Curtis and Gosling are practically the same person, separated by a few decades.

The movie: Freakier Friday, in which a mom (Curtis) gets magically brain-swapped with her adult son (Gosling), giving each a new perspective on the other's life. Hey girl, I now understand the challenge of entering menopause.

Ian McKellen -- Benedict Cumberbatch

Steely eyes, prominent nose, classical poise... Cumberbatch (star of BBC's Sherlock) and McKellen (The Lord of the Rings) could make a great old/young character pairing.

The movie: In a yet another contentious new plot addition to The Hobbit, Gandalf magically travels back in time and meets his young self, played by Cumberbatch. Logistical bonus: Cumberbatch is already working on the movie, as the voice of the dragon Smaug.

Advice actors might give their younger selves

Having an actor portray a younger version of another actor through fictional time travel is one thing. But what if these mature thespians could actually travel back in time? We imagine the advice they'd offer to their younger selves.

Arnold Schwarzenegger: "Only hire male housekeepers."

Sigourney Weaver: "Stop after Aliens. Please."

Will Smith: "Yes to The Matrix, no to Wild Wild West."

Jamie Lee Curtis: "Dye it, don't cut it."

Ian McKellan: "Don't do a damn thing differently, love."