The idea for the 2009 film "Avatar" came to James Cameron in a dream. One might be able to intuit its subconscious origins, as the strange, bioluminescent flora and fauna of Pandora, without their sci-fi context, feel very surreal and dreamlike. Cameron, upon waking, found that those bizarre dream images — of alien beings traversing a glowing forest — fit perfectly with his interests in nature, conservation, and super-advanced filmmaking technology. He invented a distant planet where...