Deep beneath the Gran Sasso mountain range in Italy, a unique laboratory is helping scientists search for one of the universe's greatest mysteries: dark matter. The Gran Sasso National Laboratory, located 80 miles from Rome, is built inside a 10km tunnel under 1,400m of rock. This natural shield blocks nearly all cosmic radiation, making it one of the least radioactive places on Earth.
The laboratory was constructed in the 1990s alongside the A24 motorway tunnel. A side entrance and additional tunnels were added to create a facility where physicists can study sub-atomic particles without interference from background radiation. Professor Cristian Galbiati, who works at the lab, explains that the thick rock roof blocks out muons—particles created by cosmic rays that bombard the Earth's surface.
Scientists at Gran Sasso are trying to detect weakly interacting massive particles, or WIMPs, which are thought to make up 85% of the universe's mass. Dark matter has never been directly observed, but its existence is inferred from the fact that galaxies spin too fast to be held together by visible matter alone. Professor Gerry Gilmore of Cambridge's Institute of Astronomy compares it to a spinning conker: the faster it spins, the stronger the force needed to keep it from flying away.
Astronomers calculate galaxy masses in two ways: by adding up visible material, and by measuring star speeds. The results consistently differ by a factor of ten, suggesting that most mass is invisible. The DarkSide-50 experiment, a US-European project set to begin at Gran Sasso soon, aims to detect WIMPs in this radiation-free environment. If successful, it could unlock the secrets of dark matter and reshape our understanding of the universe.
