Writer/director David Lowery’s ‘A Ghost Story’ shouldn’t work. It’s an existential exploration of life, death, love, loss, memory and time, in which the main character is a ghost covered by a bed sheet. That should be silly and distancing, and at times certainly feels that way. However, there’s a method to Lowery’s madness, a goofiness that undercuts the pretentions. Somehow, when the 90-minute experiment wraps up, he’s delivered not just a unique cinematic prank, but a genuinely profound film. Casey Affleck and Rooney Mara star as a couple, known only as C and M, who have perhaps been together a little too long. Love is still there, but arguments are constant. He lives in the past, she dreams of the future. For some reason, C (Affleck) doesn’t want to leave their modest house, and after an unexpected accident, he never will. He dies and returns as a ghost wearing a bed sheet with eyeholes cut out, like in a ‘Peanuts’ cartoon. It’s goofy at first and Lowery has fun with the image. (A scene in which Affleck’s ghost communicates with another bed sheet phantom in a neighboring house is wryly amusing.) Then he sticks around, long past M’s period […]