Never mind evil aliens, deadly phasers and the mysterious "wormhole" -- a sort of magic tunnel through which space travelers can zip to distant galaxies. Star Trek: Deep Space Nine is one series that isn't afraid of abstract theoretical concepts. In the show's premiere episode, Commander Benjamin Sisko (Avery Brooks) tried to explain the nature of linear time, the idea that the past influences the future. "That is the essence of linear existence," he said. "Each day affects the next."
TV has its own version of linear existence: each hit show affects the next. Star Trek, the old NBC show and...