The 2012 discovery of the Higgs boson was a sensational triumph—the culmination of a 48-year-long search that put the finishing touches on the so-called “Standard Model” of particle physics. While the celebrations were still underway, researchers in China were making plans to continue the centuries-old quest to identify the fundamental building blocks of nature. More specifically, they began laying the groundwork for a giant accelerator—up to 100 kilometers in circumference—that would transport physics into a previously inaccessible, high-energy realm where a host of new particles, and perhaps a sweeping new symmetry, might be found. The case for such an instrument is compelling: Even though the Standard Model can describe the behavior of particles with astounding accuracy, it is incomplete. The theory has little to say about the Big Bang, gravity, dark matter, dark energy, and other far-reaching phenomena. This book explains how an ambitious new machine—on the scale of China’s proposed “Great Collider”—could provide us with a fuller understanding of the origins of our universe and its most basic constituents.