Love and loss go hand in hand in “20th Century Women,” a funny, emotionally piercing story about a teenager and the women who raise him. It opens in 1979, when cool kids danced to Talking Heads and President Carter bummed everyone out talking about our “crisis of confidence.” There’s something in the air – or so it seems, although the California light here tends to blot out the shadows. When a car bursts into flames soon after the movie opens, it looks about as threatening as an art installation.

The car belongs to Dorothea Fields – a thrilling Annette Bening – a divorced single mom with an only son, the teenage Jamie (Lucas Jade Zumann, in a heartbreakingly sincere turn). Mother and child live in Santa Barbara, that drowsy, well-heeled coastal city north of Los Angeles.

There, Dorothea is raising Jamie in a roomy, stately 1905 fixer-upper that she’s renovating with the help of a boarder, William (Billy Crudup). Another lodger, an artist, Abbie (Greta Gerwig), helps keep their communal life jumping, as does Jamie’s friend Julie (Elle Fanning), who likes to cuddle platonically with him at night, sharing secrets as he tries to keep his hormones and body from betraying him.

Writer-director Mike Mills’ last movie, “Beginners,” was a lightly comic, fictionalized weepie about his father, who came out of the closet in his mid-70s when his son was an adult. Now Mills has turned to his mother, in another fictionalized story, moistened with tears, that draws on his life. This time, though, he has turned back the clock for a portrait of his mother as she was when he was a teenager and didn’t yet entirely grasp her extraordinariness.

Whether she was as remarkable as the woman onscreen seems entirely beside the point – “20th Century Women” is a memory movie, one in which people are conjured up to bump against the larger world, exuberantly and uneasily.

The personal is the political, as second-wave feminists liked to say, and so it is in “20th Century Women.” The politics sneak up on you, filtered through the intimate lives of its electrically alive characters. Jamie is the story’s hub, the center from which everything and everyone ostensibly radiates, but Dorothea is its reason for being. She sets the pieces into place and motion; she’s the inspiration and guiding spirit, the story’s balm and soul. She’s also the one who, after Jamie lands in the hospital after a heart-leaping, foolish stunt, enlists Abbie and Julie to help raise Jamie. Dorothea’s a with-it mom, from tousled hair to Birkenstocked toe, but she’s also unsettled by the world.

Abbie and Julie assume their responsibilities seriously. Julie, who smokes like a Frenchwoman and reads Judy Blume, shares battle stories and wounds from the sexual front. Abbie gives Jamie records and books, including “Our Bodies, Ourselves,” that liberatory classic about women’s health and sexuality. It’s as eye-opening for Jamie as “Sisterhood Is Powerful,” the radical feminist anthology that he first opens with almost spiritual reverence – or is it trepidation? Jamie’s sentimental education is also a kind of encounter session.

It’s a witty and loose coalition of like minds, complete with skateboarding, dancing, loving and lived-in talk. A lot of that chatter is humorous, but there’s also a powerful undertow of loss running through the movie. There are sorrows and tragedies, one involving a story thread that allows Gerwig to root around in grief and a scene in which she uncomfortably, hilariously, clears the room. For her part, Fanning drifts in and out like a dream, a magnificent emissary from that seductive land called Young and Beautiful. You simultaneously see the girl Julie is and the girl that she’s on the verge of leaving behind.

For a memoirist, Mills is uncommonly generous. Abbie, Julie and William, who sexily floats around the periphery (Crudup is superb at not quite stealing his scenes), are so persuasively detailed that all three could spin off into a separate movie; each has both sting and tenderness nearing grace.

Yet these three and even Jamie pale next to Dorothea, who’s satisfyingly complex, especially for a movie mother. Dorothea is at once laid back and uptight, which Bening conveys with moments of shambling, gestural looseness and sudden emotional spikiness. She floods the screen with warmth, threatens to burn the joint down and, with Mills, turns contradictions into character.

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