Our universe isn’t just described by mathematics, but it is mathematics. Specifically, it’s a mathematical structure. Our world doesn’t just have some mathematical properties: it fundamentally has only mathematical properties. Why is mathematics so spectacularly successful at describing the cosmos? In this Ri talk, MIT physics professor Max Tegmark proposes a radical idea: that our physical world is not only described by mathematics, but that it is mathematics. He shows how this theory may provide answers to the nature of reality itself.