On September 10, 2008, operators at CERN sent a beam of protons all the way around the Large Hadron Collider for the first time. The ring is 27 kilometres in circumference, buried about 100 metres below ground under the countryside north of Geneva, on both sides of the French-Swiss border. It had been under construction since 1998 and cost several billion euros.
The machine works like this. Two beams of protons run in opposite directions around the ring, and collide at four points where detectors sit: ATLAS, CMS, ALICE and LHCb. The beams are guided and squeezed by superconducting magnets cooled by liquid helium to about 1.9 kelvin, colder than outer space, and each proton is accelerated to an energy of 7 teraelectronvolts. The point of it is to look at what comes out of collisions at energies not seen since the first moments after the Big Bang.
Nine days later it broke. On September 19, 2008, a splice between two magnets failed during a test at high current. The electrical arc burned through the helium containment, about six tonnes of liquid helium escaped into the tunnel, and the resulting pressure wave shifted 53 magnets off their mountings. Repairs took a year. The first collisions at usable energies came in November 2009.
The machine's headline result arrived on July 4, 2012, when the ATLAS and CMS collaborations announced they had found a particle with the properties of the Higgs boson, at a mass of about 125 gigaelectronvolts. The Higgs is the last fundamental particle of the Standard Model to be observed and the one that explains why other particles have mass, and its existence had been proposed in 1964 and searched for in one form or another ever since. Peter Higgs and Francois Englert shared the 2013 Nobel Prize in Physics.
Since then the collider has run through two long shutdowns for upgrades, and it has also produced results nobody predicted, including the discovery of pentaquark states and increasingly precise measurements that have closed off large areas of supersymmetry theory. No new physics beyond the Standard Model has been confirmed.