Eleven-year-old Nora K. received Jostein Gaarder's Sophie's World as a birthday present, and in it she read about Plato's theory of ideas. One problem especially intrigued her: What about the platonic idea of the dinosaur? Ideas are timeless and cannot die. The dinosaurs, however, became extinct ages ago. Does the idea of the dinosaur still exist all the same? Could it ever be that the material world is a dream and time an illusion? Moreover, is there such a thing as free will, or is everything predetermined? Is the soul eternal? Do animals have a consciousness? Is the universe infinite? Is...