Book excerpt: "The Higgs boson ... is the key to understanding why mass exists and how atoms are possible. After billions of dollars and decades of effort by more than six thousand researchers at the Large Hadron Collider in Switzerland--a doorway is opening into the mind-boggling world of dark matter and beyond. Caltech physicist and acclaimed writer Sean Carroll explains both the importance of the Higgs boson and the ultimately human story behind the greatest scientific achievement of our time"--Publisher