Cerebral science fiction is almost by definition pessimistic.

For all that we can speculate and imagine and conceive as within the realm of the possible, that nagging knowledge of human nature, almost unshakeable if not immutable, casts a shadow over hope and puts a dent in dreams of “boldly going where no one has gone before.”

“Aniara” is science fiction cinema from the land of Bergman and Strindberg — sharply observed, just brittle enough to fend of sentiment, bleak when bleak is what is called for.

The Swedish drama — aptly-enough based on a poem — is about a space ship cast adrift, a slow-motion disaster film where pluck and hope get shouted down and human nature is laid bare via “Lord of the Flies” and “Mutiny on the Bounty” touches.

It’s hard not to see this quietly compelling picture as a metaphor for life on Earth today. Heaven knows it’s an easy case to make.

The Aniara is a vast space transport ship, loaded by Space Lift, the space elevator concept we’ve been reading about in recent years, wholly realized.

Cataclysmic opening credits show us an Earth in environmental collapse, and many of those riding Space Lift skyward wears scars. A toddler is asked (in Swedish, with English subtitles) “Want to wave goodbye to Earth?”

“NO.”

They’re leaving behind a failed planet, boarding a vast cruise ship with 21 restaurants, a sauna, bowling alleys and pitching cages, a mall in space — clean, uncluttered and white in the soft glow of artificial lighting.

A motherly figure (Anneli Martini) welcomes all aboard, a video tour guide to the amenities of this Viking Line version of a space ark.

“We wish you a pleasant voyage and a happy new life on Mars.”

Off camera, in her cabin and talking to her roommate (Emelie Jonsson), she is less sanguine.

“I’ve never been all that impressed with people…I hope they all melt into the tarmac.”

The 23 day trip on a roomy ship with algae-cleansed air and an experienced crew should be a breeze. But if it isn’t, the roommate, MR (Jonsson) is hostess for Mima, a “travel to a happy place in your mind” auditorium which customizes VR/”Star Trek” holodeck experiences, allowing MR, for instance, to retreat to the woods near a Swedish lake, walking barefoot, skinny dipping.

She has few takers on Day One of the voyage. That will change.

We’ve seen bits of space junk, and sure enough there’s a collision. The uniformed staff order everybody to “Just lie down,” and when the sharp maneuvers end, offer a reassuring “Now all is in order.”

On the bridge, they’re seeing the point of impact and flashing “Meltdown Imminent” (in English) warning lights.

Whatever the captain (Arvin Kananian) tells them, that they’ve been knocked off course and have lost propulsion, that they’re merely delayed, finishing with “Be thankful for what we have” and “Be there for one another” is a lot less assuring.

Passengers, being human, focus only on the positive, gripe about not being on Mars “for my son’s birthday” and let “Have some snacks, courtesy of the captain” placate them.

MR, sharing her room with the motherly cynic who turns out to be an astronomer, gets the unfiltered truth.

Co-writers/directors Pella Kågerman and Hugo Lilja break “Aniara” into chapters covering the passage of time — “Day One: A Routine Voyage,” “Week 3: Without a Map.”

We see the hapless ride guide hostess MR grow in importance as passengers flock to her “happy place” experience to cope with the stress of the extended voyage. And they don’t even know how extended it may be.

“We’ve built our own little planet,” the captain tells her privately. Help them get used to it.

And they, including MR, do — meeting and mating at the techno-discotheque, training for new “jobs” on board, doing their best to tamp down fatalism and despair.

MR finds sex and love, but The Astronomer — SCIENCE in big letters, in case you miss the metaphor — isn’t sugar-coating anything. Whatever the company-appointed leadership says, she’ll pass along the straight dope to anybody who asks.

Jonsson, the downbeat ship’s officer Isagel (cq) played by Bianca Cruzeiro, Kananian and  Martini each shine in giving us narrow pieces of human expression — optimistic but frightened (Jonsson), determined-to-maintain a facade (Cruzeiro), fatalistic and power drunk (Kananian) and just fatalistic (Martini) get their moments in the spotlight.

“Anaira” shares its plausibility, story arc and much of its tone with the bloodier and more melodramatic “High Life,” which is winding down its limited release run just as this one opens. But the Swedish film scores over the earlier one in its straightforward treatment of the subject, its production design and in more ambitious dissection of human nature.

But both are parables, microcosms of isolated society parked in the uninviting vastness of space. “Aniara” may have a dour Swedishness about its outlook, but with every day’s dire warnings about mass extinctions, dying oceans and a grim future chased off the front page by royal births and moronic tweets, you have to figure they’re onto something.

MPAA Rating: R for strong sexual content, graphic nudity, disturbing images, and drug use

Cast: Emelie Jonsson, Bianca Cruzeiro, Arvin Kananian, Anneli Martini

Credits: Written and directed by Pella Kågerman and Hugo Lilja, based on a Harry Martinson poem.  A Magnet/Magnolia release.

Running time: 1:46