Explore the mathematical models behind the spread of diseases, ideas, and internet phenomena in this 55-minute lecture from The Royal Institution. Delve into the predictability of various outbreaks, from malaria and Zika to SARS and COVID-19, and understand why some never materialize. Discover how similar mathematical principles apply to the propagation of fake news and memes. Learn about the factors influencing disease transmission, including the impact of isolation, contact tracing, and quarantine. Gain insights from real-world examples such as the ice bucket challenge, HIV control strategies, and COVID-19 transmission chains in Hong Kong and the UK. Understand the complexities of estimating infection sources and the importance of clear symptoms in successful containment efforts.