Often, when we physicists ask the right questions, we realize that even the most commonplace parts of our world remain deeply puzzling. In its 125th anniversary issue, Science magazine asked many such questions. 1 My eye was caught by, “What is the nature of the glassy state? … Where and why does liquid end and glass begin?” I chuckled, partly because I knew the editors had made a perceptive choice, but also because I had just wandered inadvertently into that field of research and was beginning to appreciate its depth and subtlety. I also was learning that glass physics is a highly contentious subject—a sure sign that there is still a lot to learn about it.
My curiosity-driven excursion through glass physics started more than a decade ago with fracture and earthquake dynamics. I decided to look at amorphous solids because I thought their liquidlike structure would make them easier...
