Alexander Payne has become known for directing bittersweet comedies rooted in recognizable — you might say warts and all — humanity. Movies like “Nebraska,” “About Schmidt” and “Sideways” are not always easy on their characters, but they sometimes crackle with lightning bolts of insight.

Payne’s latest, written with his frequent writing partner, Jim Taylor, adds a sci-fi framing device to his work. But ultimately “Downsizing” looks a lot like his previous films — and I think that’s a good thing.

The gimmick here is that Norwegian scientists have discovered a way to shrink people, a breakthrough that will lead to enormous environmental and financial benefits for the planet. Regular guy Paul (Matt Damon), who’s never made it big in life, convinces wife Audrey (Kristen Wiig) that downsizing could be their ticket to happiness. You don’t need to be rich to live in a lavish home when that home is the size of a dollhouse.

Or so goes the pitch of an old friend (Jason Sudeikis) who’s now living it up in a teeny-tiny planned community. However, things don’t quite work out the way Paul expects. You still have noisy neighbors upstairs, and you still have to fill the hours. No matter your size, you’re still stuck with yourself.

After a splendid and wacky opening half-hour, when Payne and Taylor have enormous fun detailing how exactly downsizing works, the movie shows its philosophical side. Paul’s world opens up in different ways, especially after he meets his devilish upstairs neighbor (the guy making all the racket), a Eurotrash swinger scrumptiously played by Christoph Waltz.

The eternally otherworldly Udo Kier, who really needs some kind of arthouse-cult-icon award, plays Waltz’s buddy; the two of them manage to keep “Downsizing” funny during the lull of its middle section.

We also meet a former human-rights refugee, now housekeeper, Ngoc Lan Tran (played by Hong Chau, who did wonders with a small part in “Inherent Vice”). This character, who helps Paul develop a conscience as they are drawn into a far-fetched plot about the future of humankind, takes the film in the direction of sincerity, which is not always an easy fit with Payne’s social satire. But it works.

The heavily accented, hard-laboring Ngoc has come under fire from some critics, who detect caricature in the portrait of a person of color leading a white guy to enlightenment. The problem with this criticism is that everybody’s a caricature in “Downsizing”— from the premise on, this is a movie in an exaggerated style — and Hong Chau’s performance is too strong to be dismissed.

“Downsizing” isn’t perfect, but its saving grace is the loopiness of its basic idea. Any time the film seems to be getting just a little self-important, there’s a sight gag involving a gigantic saltine cracker. (I guess the cracker is normal-sized and the people are small, but you know what I mean.)

There’s also the anchoring presence of Matt Damon, who wears the right air of vague disappointment through most of the film. In fact, it’s a huge relief when Paul ingests some Ecstasy at one of his neighbor’s parties and finally relaxes. Damon puts a big dopey grin on his face, and Paul looks 10 years younger and light-years sillier.

“It’s quite wonderful to be small, don’t you think?” says Udo Kier, with the lilt of the slightly deranged. There’s something touching at the heart of this movie, just as there was in the thoughtful ’50s sci-fi classic “The Incredible Shrinking Man,” which is that if we could stop thinking that we’re big in the universe, we might appreciate what has meaning within our cosmic insignificance.

Payne is a little sentimental in putting together the elements, but it sure is enjoyable watching the molecules fall into place.

“Downsizing” (3½ stars)

Matt Damon takes advantage of new technology that reduces humans to teeny-tiny size, and finds that the advantages of being small aren’t all they’re cracked up to be. Alexander Payne’s social satire isn’t perfect, but it has memorable characters and some splendid sci-fi sight gags. With Christoph Waltz, Hong Chau.

Rating: R, for nudity, language, subject matter

Opening Friday: