String theory and the real world

We live in exciting times for particle physics. The Large Hadron Collider (LHC) at CERN has begun to collect data, and laboratory and satellite experiments are investigating the dark matter of the universe. Another, less appreciated fact increases the excitement. Physicists now have a coherent, consistent theoretical framework to address basic questions about particles, the interactions and forces between them, why they are what they are, and how numerous phenomena are related in a broader picture. That framework is “string theory.” I put the term in scare quotes because there is not yet a final formulation of the theory. But the lack of a finished picture is not important for my purposes, so in this article I refer to the framework as string theory or M-theory. The perspective that string theory is the underlying framework to address many issues facing particle physics and cosmology is different from the more standard...