Particle Time Machine

The Large Hadron Collider, a 17-mile-long underground ring run by the European Organization for Nuclear Research (CERN) near Geneva, began colliding lead ions together Nov. 8. These atomic nuclei contain 82 protons, and are much heavier than the lone protons the accelerator was previously colliding. Now two experiments at the LHC—called ATLAS and CMS, respectively—have reported a phenomenon called “jet quenching” that scientists say could reveal secrets about the nature of matter and the evolution of the universe.