Particle tracks and cosmology. Conceptual computer illustration of a male outline on subatomic parti- cle tracks (yellow spirals & lines), geometrical shapes and a glowing nebula. This represents the attempt by humans to understand the universe at a subatomic level. 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. Nebulae are astronomical features formed from giant clouds of gas and dust.