Francis Ford Coppola’s Megalopolis, a movie the 85-year-old director began making decades ago, is fixated on the future. The film’s characters, all members of a fableized city-state elite in the moments leading up to the fall of the American empire, wax philosophical about it constantly: about who will hold power, what civilization will look like, matters of inheritance, succession, growth, and decay. But the most effective expression of the film’s futurism isn’t in the...