Invented in 1952 by the late Donald Glaser, then at the University of Michigan, a device called a bubble chamber allows scientists to trace the paths of high-energy, charged particles rocketing through a superheated liquid. Ionizing particles leave trails made of expanding bubbles, and the shape of these trails provides clues about the identity of the particles and how they decay. For example, lightweight electrons and positrons lose energy quickly, creating spirals. Particles that elude collision leave straight, parallel tracks. This classic 1960 photograph shows tracks in the first liquid-hydrogen bubble chamber at CERN, the European laboratory for particle physics near Geneva. A negatively charged pion interacts with a proton in the liquid hydrogen and generates sprays of new particles, including a neutral lambda particle that decays into a pair of lighter, charged particles—creating the V shape seen in the center of the image. Glaser won the 1960 Nobel Prize in Physics for his invention of the bubble chamber, which led to the discovery of new particles. These days physicists view particle tracks using monster electronic detectors that can observe hundreds of millions of events per second. —The Editors
