You'd think physicists would be delighted. In cosmology, satellite observations of the universe repeatedly confirm scientists' picture of its composition and history. In particle physics, the discovery of the Higgs boson and measurements of its properties give equally compelling evidence that their "standard model" of elementary particles and force-generating symmetries explains everything it's supposed to. And that's the problem: It's hard to develop new and better models when the old ones stubbornly refuse to break down. To keep progress from grinding to a halt, physicists are devising ingenious new experiments aimed at shooting holes in their reigning theories—but no one knows which of them, if any, will hit the mark.