Despite the book’s somber, scientific backdrop, “Solar” is Ian McEwan’s funniest novel yet. Ian McEwan has long had a penchant for creating unsavory, disreputable characters: children who bury their mother in the basement (“The Cement Garden”), a Machiavellian sadist who preys on a pair of middle-class tourists (“The Comfort of Strangers”), a dead woman’s conniving former lovers (“Amsterdam”), an adolescent girl who makes false accusations against a man that will alter his life and the life of her entire family (“Atonement”).