In the fall of 2008, the world’s largest particle accelerator, the Large Hadron Collider, or LHC, began operations for the first time. Circulating beams of protons under the Swiss and French countryside, the accelerator generated worldwide excitement. A disappointing technical malfunction delayed collisions, but scientists expect to turn the machine back on in October.It is only a couple of times in a lifetime that a new particle accelerator is launched that can explore an entirely different energy frontier. The Fermilab Tevatron was in 1983 – a quarter century ago. It is expected that the new LHC will dominate the research landscape for the next decade or two.The Quantum Frontier: The Large Hadron Collider tells the story of this magnificent scientific instrument.The book’s first chapter is about what we already know, the context for the exciting measurements we expect.The second chapter reminds that we don’t actually know what the LHC will discover; this is truly terra incognita. However, I do discuss three of the interesting questions the LHC was built to investigate: (1) the elusive Higgs boson, sometimes called the God Particle; (2) supersymmetry, which predicts many new particles and would shed light on a few unanswered questions; and (3) the intriguing possibility that the smallest particles of which we are aware are themselves composed of even smaller particles. (These “smallest” particles are quarks and leptons—current theory treats both as containing nothing within them. The most familiar lepton is the electron; quarks are found inside the familiar proton and neutron.)The third chapter is about how particle accelerators work and about many of the amazing features of the LHC—including the temperature of the magnets (colder than space itself) and the vacuum in the accelerator (ten times better than the surface of the moon).Chapter four is about how particle detectors work, and describes the four major detectors arrayed around the LHC’s ring. Two of these detectors include in excess of a hundred million distinct pieces each.The fifth chapter takes a broader view. Staring deep into the cosmos, astronomers have found that fully 95% of the matter and energy in the universe is of totally unknown kinds. What might the LHC say about these mysteries?There are other accelerators under consideration and upgrades of older ones. In addition, not all mysteries are found in a particle collider environment. Yet it is deeply intriguing that an accelerator here on Earth can perhaps answer mysteries that span the universe. The Quantum Frontier closes with a discussion of some of the broader issues that contemporary scientists are trying to tackle. It’s a heady time for physics enthusiasts; a paradigm-changing discovery could be just around the corner.