Anatomy of an atom

In the second half of my story, the three strands of relativity, quantization and symmetry will be braided together. Before we embark on this journey, let us take a rest and consider some ways in which the properties of the small-scale quantum world govern our world at large. Most people wonder about the relevance of subatomic studies for our understanding of ourselves. Quite a few popular accounts of particle physics contain a heavy dose of reflections upon Larger Issues and related Deep Thoughts. I will try to avoid that, but it cannot be denied that the connections between the subatomic scale and our daily world are strong and direct, albeit invisible to our large-scale senses.

Let us first consider atoms, the building blocks that have the most direct significance in our daily lives (in the remaining chapters we will discuss the structure of the particles of which atoms are made). For simplicity and definiteness, and because we have encountered it in previous discussions, I will mainly speak of the hydrogen atom. Its nucleus is a proton, having one unit of positive electric charge. A neutral hydrogen atom is formed when an electron, bearing one negative unit of electric charge, binds to it. The binding makes the atom electrically neutral.