It's by far the biggest, most complex scientific experiment ever built, and when the Large Hadron Collider goes online in November, the payoff will be equally gigantic. The LHC, nearing completion in a huge circular tunnel more than five miles across and 300 ft. underground that straddles the border between France and Switzerland, will put the finishing touches on the venerable Standard Model of particle physics or demolish it.
Either way, physicists can't wait. The Standard Model, painstakingly cobbled together over the past century, lacks one particle the so-called Higgs, which gives other particles their characteristic masses. To find it, physicists at the LHC will whirl beams of protons in opposite directions around the tunnel's 17-mile circumference over and over until they reach 99.999999% of the speed of light. Then the beams will smash together in a burst of energy, which in turn will condense into new particles and with any luck, some of them will be Higgses.
If not, it's back to the drawing board. But even if physicists find the Higgs, the Standard Model will eventually have to be put aside in favor of a theory that merges quantum theory and relativity. With luck, the LHC could find all sorts of new particles, or even new dimensions, that might provide hints of what that new theory will look like.