Michael Sigman: Roger Nygard’s new documentary The Nature of Existence gives us a good-natured glimpse into the imaginations of brilliant thinkers from science, religion and other disciplines on life’s fundamental questions. If we try to let our imaginations run free and work shoulder to shoulder on real problems instead of fantasizing about self-aggrandizement — my own particular fave being high school basketball greatness — maybe we can become an imagine-nation and begin to turn things around.