Particle tracks. Conceptual computer illustration depicting the increasing human understanding of particle physics as two heads viewing subatomic particle tracks (white spirals). The coloured points represent particles. The tracks result from energetic charged particles moving through a bubble chamber containing a superheated liquid. Ionisation of the liquid by the particles causes it to boil, so that tracks of minute bubbles are left in their wake. Each particle creates a distinct track, such as the spirals made by electrons and positrons. Particle physics has revealed the basic structure of the atoms from which everything is made.