“Our planet is a spaceship, and this spaceship needs a change of course.” In his ninetieth year the Nicaraguan poet, politician and former priest Ernesto Cardenal looks back on a multifaceted biography, as an alert and combative intellectual, anything but mellowed by age. In four conversations he talks about his life in the service and tension of faith, politics and poetry, and asks about the conditions of a better world. The Magnum photographer Susan Meiselas accompanied the Nicaraguan revolution; her pictures are so close to events that one can see and feel the fear and violence.