When President Trump announced last year that the US might resume nuclear weapons testing, it raised a question the world hasn't had to seriously consider in decades: what happens if they do?

In this episode, Liz Williams sits down with Professor Trevor Findlay, a nuclear governance expert who was involved in the early diplomatic work that became the Comprehensive Nuclear Test Ban Treaty (CTBT). The CTBT exists, the monitoring network is nearly complete, and the organisation behind it is operating, but the treaty never entered into force. What would states would actually do if testing resumes? In this conversation, Trevor shares insights into how the treaty and accompanying verification system was built, why it was designed the way it was, and what it all means now ...