What does it mean to say something has 2 dimensions, or 3? Einstein’s general theory of relativity describes our universe as having 4 dimensions, while string theory says we live in a 10 or 11-dimensional space. In modern mathematics and cosmology “space” is a foundational concept, but what do scientists mean by this term? And what are the “dimensions” they speak about here? In 1929, Edwin Hubble discovered that space is expanding, while around black holes physicists tell us that space stretches. How can we understand such statements? In this deeply engaging lecture, Wertheim discusses the history of scientific concepts of space from the Middle Ages to string theory.