WIMP detector. Artwork of Boulby mine, site of the UK Dark Matter Collaboration (UKDMC) project which searches for Weakly-Interacting Massive Particles (WIMP). About 90% of the universe's mass may be invisible dark matter such as WIMPs, the rest be- ing visible matter such as stars. The UKDMC site in Britain is the first to be funded solely to look for WIMPS. Its detectors (at lower right) are 1100 metres underground in Europe's deepest mine so that the rock above it blocks cosmic rays (blue lines). WIMPs (yellow lines) are to be detected by observing the recoil energies of normal nuclei after a collision with a WIMP, a rare event due to the WIMPs' weak interaction with other matter.