Written only a few years after the atomic bombs dropped on Hiroshima and Nagasaki ended World War II, Arthur C. Clarke’s “The Sentinel” contains several themes that would become common in Cold War science fiction. Reflecting a shared dread that humanity might entirely destroy itself through nuclear war, many authors viewed the advent of a nuclear era as being a universal rite of passage for any civilization. While harnessing nuclear reactions was considered necessary for scientific advancement, it also provided a means for planetary self-annihilation. All civilizations advancing to the level of nuclear weapons, therefore, must learn to transcend their base instincts. Only after successfully accomplishing this rite of passage, thus assuring the continuation of planetary life, can a race begin a new phase of space exploration and alien contact.

A second theme, first encountered in “The Sentinel” and appearing throughout much of Clarke’s later fiction, is the presence of a vastly superior civilization, one whose existence predates human civilization by unknown millennia. It is a patient race, observing the evolutionary development of more primitive species throughout the universe, presumably awaiting their maturation. Childlike humans, themselves only newly sentient, can only guess at the intention of the superior race, hoping it is benign rather than sinister. Even in their scientific investigations, humans are portrayed as childlike. When...