A post-apocalyptic Earth, emptied of humans, seems like the stuff of science fiction TV and movies. But in this short, surprising talk, Lord Martin Rees asks us to think about our real existential risks — natural and human-made threats that could wipe out humanity. As a concerned member of the human race, he asks: What’s the worst thing that could possibly happen?

Martin Rees is a Fellow of Trinity College and Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge. He holds the honorary title of Astronomer Royal and also Visiting Professor at Imperial College London and at Leicester University. After studying at the University of Cambridge, he held post-doctoral positions in the UK and the USA, before becoming a professor at Sussex University.