Leslie Rosenberg's attempt to understand the universe resembles a makeshift home hot-water heater tank, capped with some wires and shoved into a large, underground refrigerator. The experiment, housed in a laboratory adjacent to his office at the University of Washington, is a supercooled, magnetized vacuum chamber equipped with a sensitive detector that listens for the microwave “ping” of passing particles called axions. These particles are invisible and, so far, entirely hypothetical.