Richard Panek explains how we know that only 4 percent of the universe consists of the matter that makes up people, planets, stars, and galaxy. The other 96 percent of the universe is completely unknown. The 4 Percent Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality tells the story of how scientists reached this conclusion, and what they’re doing to find dark matter, dark energy, and to help paint a complete picture of the universe.