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Stars and other visible objects make up about 15% of solid matter in the universe; the other 85% is invisible. Astronomers have known this since 1932, but only recently has the hunt for dark matter taken off. Schilling begins with a disclaimer of sorts: “Despite decades of speculation, searching, studies, and simulations, dark matter remains one of the biggest enigmas of modern science.” Rather than follow the traditional format by beginning with the history (and easy concepts) and proceeding toward more complex ideas, the author offers a series of interesting chapters, many of which could stand alone. He chronicles his interviews with scientists around the world and often rewinds the clock to earlier discoveries that foreshadow today’s massive but still frustrating efforts. Early in the last century, astronomers discovered that stars were moving too fast. Just as planets circle the sun, stars circle their galaxies. Since gravity diminishes with distance, outlying planets move more slowly, but this wasn’t true in galaxies. Outlying stars were not slowing. Gravity controls movements, so galaxies had to be much heavier than predicted. At first, astronomers assumed that gas, dust, and small solid bodies made up the difference, but these were never found. By the 1980s, scientists concluded that this “missing mass” represented particles unknown to science. They’re still unknown, but researchers keep searching. Curious, indefatigable, and a fine writer, Schilling clearly relays the work of astrophysicists, some of whom denigrate the work of colleagues. Great telescopes and other instruments on Earth and in space work their magic, but they reveal only hints of dark matter. The discovery of dark energy created yet another significant enigma. “Over the past two decades,” writes the author, “the pie diagram of the composition of the universe—68.5 percent dark energy, 26.6 percent dark matter, and 4.9 percent familiar stuff—has become an iconic representation of our cosmic ignorance.”

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