Hilde wakes up and realizes that she dreamed that she was sitting on the dock hearing Sophie's voice when her father came home. Then Hilde begins to read again, and she follows Sophie as she tries to distract Albert Knag from Alberto. Sophie climbs a tree, gets stuck, and is flown down by a goose that first makes her smaller so she can ride. Sophie gets home and helps her mother prepare for garden party before going to sleep. The next morning, Sophie meets Alberto in town, although he shows up late, claiming he did so on purpose. Then Alberto begins to talk more about existentialism. He focuses on ##Sartre# who felt that existentialists have nothing but humanity to go on. He was an atheist who believed that because people are conscious of their existence, their "being" is therefore different from that of things. Sartre thought that there is no general human nature but rather that we must create our own. He viewed our freedom as a burden, since we arrive in the world free whether we like it or not. We must assume complete responsibility for our actions and find our own meaning in life through the use of our consciousness. Simone de Beauvoir, Sartre's companion, argued further that male and female natures do not exist.
Alberto then points out that modern science is still dealing with many of the questions that the ancient Greek philosophers asked. And what is special about philosophical questions is that they must always be asked over the years and cannot be answered in any permanent sense. He speaks of new trends and warns Sophie not to pay attention to all of the so-called New Age science that is really just superstition passing as science. Alberto tells her that publishers publish what people want to read, not necessarily good books. He debunks some of the ideas of the supernatural and says that nature itself is magnificent enough. Before Sophie leaves Alberto buys her a copy of Sophie's World, which sits on the philosophy shelf in a bookstore
Hilde pauses in her reading to think about the way that her father has managed to send so many messages to her in the book. Then she reads on. Sophie bumps into her mother on the bus ride home and her mom reads a bit of Sophie's World but does not seem too surprised. They make it through a demonstration on their street and then spend the rest of the day preparing. Joanna helps them set up the next day. The guests begin to arrive, and soon everyone waits for Alberto. Alberto arrives late, sets off a few firecrackers, and sits down after Sophie's mom makes a short speech. Suddenly Joanna begins kissing Jeremy, one of the boys. Soon, Joanna and Jeremy are rolling in the grass together while everyone except Sophie and Alberto watches. Alberto tells everyone the truth about their existence—that they are all merely figments of the imagination of Albert Knag. Things begin to get out of hand, and Alberto and Sophie disappear just as the book comes to a close.
The absurdity of Sophie's party points to the fact that we do not know any truths about life. We do not know what happens after death or whether the world is real. We have no answers to the philosophical questions that have been posed in this book. But everyone acts as if they have already been answered. At the party, everyone acts very strangely, and it seems that the only two people acting normally are Sophie and Alberto, who know that everyone else is merely a collection of neurons in the brain of Hilde's father. Even if the world is real and we actually have discovered some of the laws that govern the universe, there are other questions that render our knowledge useless. For example, we will never be able to discover a law that tells us how to live a good life. No one can know what lies beyond the universe. There are a host of things that we will never have any certain knowledge about, and they apply directly to our lives. So in a sense it is our certainty about life that is really absurd. What reasons do we have to act the way we do? Gaarder wants us to take a look at the way we live and to attempt to think out for ourselves how we want to approach life. Most people act the way they do because of their upbringing and the society that they live in. But those are terrible indicators as to how one should live because they can never answer the intensely personal question of meaning. Religion may seem to give people those answers, but Kierkegaard pointed out that everyone must struggle with faith on an individual level. He believed that nothing less than our existence is at stake. Sartre was not religious, and so he felt we have nothing but ourselves to fall back on.
Gaarder seems to wholeheartedly embrace existentialism. Although all of the other philosophy that has been studied has much to offer, it seems clear that one must find meaning within life. Therefore on one level we all must come to terms with the world in our own way. However, although the meaning must be personal, that does not mean that we must be alone. Sophie and Alberto work together throughout the book and community, family, or friends may help to provide that very meaning that we all search for. The critical thing is that we all try to come to some sort of understanding. It will not be easy, because Alberto and Sophie show us that life does not come with a meaning attached to it. Their existence was solely to please Hilde, but they attempted to get something else out of life. In the same way, even if we all exist only as an experiment by a higher being, we must still attempt to get what we can out of life. But we must not make the mistake of living our lives according to a set of values that turn out not to really hold any meaning. That would be a true tragedy. Alberto does not want Sophie to live that way, Albert Knag does not want Hilde to live that way, and clearly Gaarder does not want us to live that way. Nothing could be worse than realizing at the end of one's life that everything, all the actions and events, were meaningless. And if we accept some gift-wrapped societal meaning that may be exactly what happens in the end. If we do not grapple with the issues and the questions that cannot be answered then we will not find meaning.