"Science fiction is the branch of literature that perceives the universe through the widest-angle lens. Unlike the mainstream of literature, which attempts, more or less, to depict the real world and real people in present or historic situations with the maximum amount of verisimilitude, science fiction acknowledges from the start that it is fantasy, that it is not depicting that which is or that which has been but is engaging in assaying the actions of people and things against backgrounds of limitless imagination."