It’s not much of an exaggeration to say that electrons form the backbone of the modern world. They are our workhorses—they bring energy from power plants to our homes and factories. They are our couriers—they carry information through circuits in our computers. Some day, they will be our providers—as the central elements in photovoltaic solar cells, they will capture the sun’s energy for our use. These current and future electronic devices rely on very precise answers to the question What do electrons do inside materials? Out of technological need and intellectual curiosity, condensed matter physicists have spent over a century discovering better and better answers—and they continue to do so today. In this post, I will try to give you a little glimpse into the form, beauty, and utility of such an answer.