The idea of the world redeemed by a helpless infant is a specifically Christian one, but here it shines out from a landscape that is bitterly stripped of faith. The people I know who have seen “Children of Men” have admired its grip, but they had to be dragged to the theatre; it’s a film that you need to see, not a film that you especially want to. I guess it should it be logged as sci-fi, yet by 2027 mankind is clearly beyond the reach of science, and the roughened pace of the film—photographed by Emmanuel Lubezki—leans away from fiction and toward the natural stutter of reportage. When a bomb explodes in Tony Scott’s “Déjà Vu,” it is tensely prepared for and filmed with a lingering gloat; when a bomb explodes in “Children of Men,” it bursts from nowhere on a dreary street. Even if you don’t buy the main conceit, the scumbled texture of the movie makes it feel not just plausible but recognizable, and Cuarón takes care never to paint the future as consolingly different. Theo doesn’t go to work in an aluminum-foil catsuit with a diagonal zip; he wears a jacket and tie. And where the cars of “Blade Runner” hovered in the ruined air, the vehicles here still trundle along on roads. The Britain of twenty years’ time, in short, will be just like the Britain of today, but worse. The sole survivors—the only citizens not to have caved in to despair—are shaggy old-timers like Jasper (Michael Caine), a friend of Theo’s who saw it coming. He lives in a forest hideaway, smokes weed, plays loud music, and still finds something to laugh about. Such is the moral of this tough, destabilizing film: the hippies were right all along.