Physics is supposed to be about the study of “stuff” (ie, matter), but can we learn anything interesting from the absence of that stuff? Have you ever wondered what it means when we say that a vacuum is actually filled with “virtual” particles popping in and out of existence? Or what actually lies in the deep, dark spaces between galaxies that make up the majority of the Universe’s volume? In this talk, I will discuss vacuums and cosmic voids, and why both can tell us interesting things about physics and the Universe.