As a genre, historical fiction typically gazes backward and poses the big “what ifs,” asking how things might have turned out had the wind blown a little differently all those years ago. Because one can only trudge through so many accounts of an alternate universe’s Civil War, it’s refreshing that Janna Levin’s A Madman Dreams of Turing Machines skirts that sort of revisionism altogether. Though the story is woven from documented facts and involves several well-known figures, the author evidently feels no need to ponder what adventures would have ensued had Kurt G