Has John, the narrator of Cat's Cradle, been transformed by the end of the book? If so, how? How does John compare to Nick, the narrator of The Great Gatsby?
I think John is transformed by the end of the novel, although his transformation is not exactly a moral one. In order to understand how John and Nick might compare, you have to understand their function as narrators, and how each relates to the story they are telling.
- Both characters are telling the story, and are part of the story. Nick and John are alike in that they both function as observers of the action, but their observation also somehow causes the action. Nick, for example, allows his house to be used for the first "date" Gatsby has with Daisy, setting in motion the events that culminate in Gatsby's death; John, similarly, is engaged in writing a book, the research for which leads to the destruction of the earth.
- Both narrators are essentially chronicling the lives of a group of people who are unknowingly working together towards a common end. In this sense, Tom, Jordan, Daisy, Gatsby, and Myrtle form a kind of Bokononist karrass.
- Both narrators witness destruction, and live to tell the tale. John is implicitly linked to Melville's Ishmael (Moby Dick), another observer/narrator who lived to tell the story of a terrible tragedy (Vonnegut's first line of the novel, "Call me Jonah," evokes both Melville and the biblical story of Jonah and the whale).
John's transformation, from observer/researcher to active participant in the plot, can be understood in many ways. I like to think of Cat's Cradle as a book about the perils and responsibilities of creativity. The ruthless scientism of Hoenikker is counterbalanced in the novel by the no-less-ruthless anti-logic of Bokononism. The convoluted plot, culminating as it does with the accidental freezing of the earth, is less an environmental disaster than a narrative one. In his movement from observer to participant, John has unintentionally caused the destruction of his story even as he finally becomes a part of it. He stops researching a book about the end of the world, and makes it happen.
Nick also undergoes a similar transformation, and, I would argue, gains a similar perspective on the fiction of which he has been a part. His argument with Gatsby about reliving the past (Gatsby thinks you can) is as much about the uses of fiction as it is about life choices. The famous final line of Gatsby ("So we beat on, boats against the current, borne back ceaselessly into the past") can be used to describe both books, and both characters, each of whom find themselves trapped in books that begin with hope and end with disaster.