Hugh Jackman has got to be the hardest-working man in show business this year between starring in the third “X-Men” film, “Scoop” and “The Prestige” and voicing characters in the animated “Flushed Away” and “Happy Feet.”

But nothing could have required more physical exertion than keeping a straight face while shooting “The Fountain,” a laughably preposterous movie.

Writer-director Darren Aronofsky has been working on this trippy sci-fi extravaganza since 1999, before the release of his harrowing drug drama “Requiem for a Dream.” What he’s come up with all these years later is just incomprehensible.

Jackman stars as three versions of the same guy over 1,000 years: a 16th-century conquistador, a present-day scientist and a futuristic astronaut. In all three he seeks the fountain of youth; in all three, he’s in love with Rachel Weisz, Aronofsky’s real-life fiancee who gets little more to do than stand there and look ethereally beautiful.

The cinematography from longtime Aronofsky collaborator Matthew Libatique is striking, though — mostly when Jackman is ascending to the stars inside a bubble with a gnarled tree sprouting from the middle of it, his head shaved in a way that inadvertently causes him to resemble Joey Lawrence on “Dancing With the Stars.” (That’s pretty much the easiest way to determine which time period we’re in, by the amount of hair Jackman is sporting.)

Some have compared “The Fountain” to “Zardoz,” the hallucinatory 1974 movie written and directed by John Boorman (right after he made “Deliverance”), in which Sean Connery (right after his sixth and final turn as James Bond) runs around a post-apocalytpic society in nothing but a ponytail and orange undies, chasing after an enormous, stone head floating through the sky.

The two share some similarities — themes of eternal life, boldly bizarre visuals, unintentional hilarity — but “The Fountain” is truly its own creation. That’s probably the most charitable thing to be said for it: There’s nothing else like it out there.

Here’s what happens, best we can tell.

Jackman, as Spanish conquistador Tomas, is sent on a mission from Queen Isabel (Weisz) to find the tree of life — and when he gets back, you know, maybe he’d like to go out with her sometime for a cup of coffee or something. In the present, he’s Tommy, a scientist whose wife, Izzi (Weisz again) is dying of cancer. He hopes that experiments he’s been doing using tree bark will lead to a cure.

And then there’s the segment in the 26th century, where he’s Tom Creo, floating around in what looks like a giant, glass Christmas ornament with that same tree of life inside of it. Occasionally he breaks off a little piece of bark and nibbles on it; sometimes Izzi comes to him in fleeting visions. Mostly he just does yoga.

Aronofsky cuts wildly among these story lines, sometimes within the same breath. But “The Fountain” has none of the breathtaking pacing of “Requiem for a Dream” or Aronofsky’s first feature, “Pi.” It feels both overbearing and truncated; the movie seems too long and yet totally unsatisfying.

It’s as if Aronofsky was so consumed with the film’s elaborately contrived aesthetics that he took no time for a little thing called character development. Jackman’s Tomas/Tommy/Tom Creo is basically a pawn within each complicated construct; Weisz’s Isabel/Izzi Creo is even less substantive. She’s more like a radiant, shimmering idea, especially when she’s all dolled up as the Queen of Spain. (Ellen Burstyn, meanwhile, an Oscar nominee for “Requiem for a Dream,” is underused in a couple of scenes as Tommy’s boss.)

Everyone involved with the movie attests to its pure, simple message of love. Maybe it’s hiding somewhere within the golden haze of the distant nebula Xibalba, where Tom’s bubble is headed. It’s hard to tell — or care.

“The Fountain,” a Warner Bros. Pictures release, is rated PG-13 for some intense sequences of violent action, some sensuality and language. Running time: 96 minutes. One and a half stars out of four.