Sometimes in this game you get to do an interview where you genuinely can say: "the person I'm about to interview needs no introduction." This is one of those occasions. But if I were to do that, it would wreck the fun of getting to introduce the interview, and why would I deprive myself of that? So, this episode, we are interviewing Lord Martin Rees. Martin Rees is one of the foremost cosmologists and astrophysicists of our time. He was made the Astronomer Royal in 1995, has been Master of Trinity College Cambridge, and President of the Royal Society. He has written more than 500 research papers across various areas of astrophysics and cosmology, including contributions to the origin of the cosmic microwave background radiation, the final proofs of the Big Bang theory, quasars, and gamma ray bursts. In the latter part of his career, he has been an immensely influential populariser of science, writing books on Cosmology such as Just Six Numbers and Our Cosmic Habitat. And he has also devoted himself to considering grand problems of the future of humanity and the existential risks that we face: his book, Our Final Century, helped to kick off the field of existential risk studies, and he co-founded the Centre for the Study of Existential Risks at the University of Cambridge in 2012. It is no exaggeration to say that a great many of the ideas that we've discussed on this show - and my own personal inspiration to study physics in the first place - owes to the work of Lord Rees, both in discovering much of the science in the first place and then again in popularising and explaining the ideas so wonderfully. I was extremely grateful that he was willing to be so generous with his time and respond to such a large range of my questions. Our interview touches on existential risks, the current pandemic, extraterrestrial life, cosmology in general, and the nature of fundamental physics.