Through a Glass, Darkly: This feature article written for a broad audience looks at some projects investigating dark energy, which theorists say makes up 70 percent of the universe. The search began two decades ago when astronomers measuring the speed of stars learned the universe seems to be expanding faster and faster. What could counteract gravity? No one knew, but it had to be powerful. This energy force emitted no light and was invisible to even our largest telescopes: thus the name, dark energy.