Subatomic-particle research has made enormous progress in the 20th Century by looking inside matter at deeper and deeper levels. It is as if we were peeling the layers of an onion in the hopes of finding more basic rules for the structure of nature. Although the concept of the ultimate building blocks of matter has been modified in several essential respects in the last century, Democritus’s idea remains at the foundation of modern science. Great experiments of the 20th century have led to the discovery of ever-smaller entities that make up what were once thought to be indivisible particles. Starting with the atom, they uncovered the nucleus, which was made of smaller particles such as protons and neutrons. These have themselves been dissected into even smaller particles. Moreover, this theory of the very small has been shown to be intimately connected to the largest scales imaginable – cosmology and the beginnings of the universe. Despite these considerable successes, this current theory nevertheless has within it the seeds of its own demise and is predicted to break down when probed at even smaller scales. By using our increased understanding we continue to peel away at the more hidden layers of truth with the hope of discovering a more elegant and complete theory. But as is the case with the onion, we must wonder whether there will ever emerge an ultimate layer where the peeling must stop.