by Veronika Meduna
After a two-year maintenance shutdown, the Large Hadron Collider (LHC) has restarted successfully this week. The world's largest particle accelerator is designed to replicate conditions immediately after the Big Bang, putting the Standard Model of particle physics to its most stringent test yet.
The accelerator is part of the European Organization for Nuclear Research (CERN), which sits astride the French-Swiss border near Geneva. The LHC is a 27-kilometre ring of superconducting magnets, and inside this underground tunnel two high-energy particle beams travel at close to the speed of light in opposite directions until they smash into other. The particles are so tiny that the task of making them collide is akin to firing two needles 10 kilometres apart with such precision that they meet halfway.
During this second research season, physicists hope to explain dark matter, gravity and antimatter. Our Changing World has covered the LHC's discovery of the Higgs Boson in 2012.
And below, you can also listen to our feature about the start of the LHC's first research season in 2008.