Credit: John Hersey

The recently completed Large ­Hadron Collider, the world's most powerful particle accelerator and most ambitious scientific instrument, is being readied to address some of the deepest questions in physics (see "The Making of a New Collider"). Hundreds of feet below the surface of the earth, straddling the Swiss-French border near Geneva, it will smash counter-rotating, seven-­trillion-electron-volt beams of protons against one another in a 27-­kilometer ring of superconducting magnets.

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