The lone special effect in this not-quite-sci-fi film from rookie director Mike Cahill is, as the title suggests, a second Earth, an orb that hangs in the sky inviting, admonishing and absorbing the projections of the characters below. It’s also a classic Macguffin, because *Another Earth* isn’t about life on a mirror-image planet but rather a meditation on grief and guilt. Co-writer and co-producer Brit Marling plays a young woman who, while driving drunk and distracted by the terrestrial twin, kills a woman and child. After getting out of jail, she forms a fraudulent but tender relationship with the man (William Mapother) widowed in the accident. Both characters live almost entirely in their own heads, yet Marling and Mapother make them riveting to watch, externalizing their pain through subtle expressions and gestures.