This is a coming of age story about a set of twins who embark on a journey of exploration in space, but one never leaves planet earth. One grows old, the other ages much more slowly due to the relativity aspects of the journey. The explorations are more than just in space and time; they also deal with the exploration of self. Like most of Heinlein's novels, this story has a delightful optimism.
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["Science fiction""rah""robert heinlein""Fictionscience fictiongeneral""Twins""Fiction""Fictionfantasygeneral""American Science fiction""Dinosaures""Fantastique""Litt\u00e9rature fantastique""Romansnouvellesetc. pour la jeunesse""Pr\u00e9histoire""Roman anglais""Children's fiction""Long Now Manual for Civilization"]