In the second part of our eternal quest to investigate infinity, inspired by this question from father and son duo Sorley and Tom Watson from Edinburgh: “Is anything in the Universe truly infinite, or is infinity something that only exists in mathematics?”

Hannah and Adam try and find something that is truly infinite, from the infinitely small particles that live in the subatomic world to the infinitely dense heart of a black hole. But how about the Universe itself? We find out how physicists go about measuring the shape of the Universe, with the help of an orange and a game of Asteroids. Plus, we consider the possibility that the Universe might be finite and have an edge. If so, what's on the other side?

Theoretical physicist Sean Carroll from Caltech and cosmologist Andrew Pontzen from University College London help us navigate our biggest question yet.

Presenters: Hannah Fry, Adam Rutherford

Producer: Michelle Martin

First broadcast on BBC Radio 4 in 2018.