This book attempts to explain why string theory may provide the comprehensive underlying theory that describes and explains our world. It is an enthusiastic view of how compactified string/M-theories, plus data that may be reachable, seem to have the possibilities of leading to a comprehensive underlying theory of particle physics and cosmology, perhaps soon. We are living in a hugely exciting era for science, one during which it may be possible to achieve a real and true understanding of our physical world.

Founded on three decades of research, this second edition covers the Planck scale, Higgs physics, supersymmetry and supersymmetry breaking, the Hierarchy problem, dark matter, inflation, hidden sectors, future colliders, testing theories in physics, possible limits to understanding, and more.