Late in “Past Lives,” there’s a scene in which two people walk down a street and silently wait for an Uber, captured in a single shot. Like the film itself, it is a deceptively simple moment, a seemingly mundane interaction that is simmering with tension and fraught with meaning, the ticking clock of the car’s imminent arrival pulling the narrative taut. It’s a deft and daring choice from filmmaker Celine Song, especially since she just lets the audience take this in, secure in the knowledge that our attentive patience has been carefully earned over the course of “Past Lives,” a film that is at once about two minutes, a day, a year, 12 years, a lifetime and many lifetimes.