Dark Matter (German: Schilf) is a 2007 novel by the German writer Juli Zeh. It was published as In Free Fall in the United States. It tells the story of a physics professor who is told he has to kill a man in order to get his kidnapped son back, and a detective, Schilf, who steps in to solve the case. As of December 2011, a German film adaptation directed by Claudia Lehmann was in post-production.