The biggest physics experiment ever, CERN's Large Hadron Collider (LHC), goes live this summer. The international project, whose design was approved in 1994, cost over $6 billion. Thousands of powerful magnets, cooled by tons of liquid helium to 1.9 Kelvin (just above absolute zero), will guide two beams of protons as they travel in opposite directions around a 27-kilometer tunnel at close to the speed of light; then magnets at two locations will pull the beams together for the highest-energy particle collisions ever achieved. By identifying the products of these collisions, physicists hope to test the standard model of physics and discover new subatomic particles. (Read Nobel laureate Jerome ­Friedman's thoughts on the LHC.)

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