Scientists have always been interested in probing the inner structure of matter. Now they have laid the foundation of a unified theory that four basic forces are responsible for the world as we know it: gravity, electromagnetic force, radioactivity, and nuclear force. Although we lack a full understanding of these forces, we have learned to make use of them for numerous purposes, from energy production to medical procedures. Experiments carried out in major physics laboratories throughout the world may enable physicists to fulfill their ultimate objective: a unifying theory describing the four major forces, a single-equation theory encompassing all of the physical phenomena in the universe. (23 minutes)