The Chile of Patricio Guzmán’s childhood is long gone, a collective history he’s explored in other films. But Nostalgia for the Light (Nostalgia de la luz), premiering on PBS on 25 October, looks at that history in brilliant new ways, articulating two searches for the past. One is a pursuit of scientific knowledge, the evidence to support theories of how life began and what might be coming for the planet earth; it’s conducted by astronomers via the world’s largest optical telescope (called the European Extremely Large Telescope, or E-ELT) located in Chile’s Atacama desert. The other, ongoing since 1990, is undertaken by the relatives of victims of August Pinochet’s dictatorship: they seek remains and stories, knowledge of how their loved ones died. Both searches, the film points out, involve bodies, material and celestial, and both are endless.