What would the world look like if Russia had won the cold war? If the Boston Tea Party never happened? And where would we all be if Guido van Rossum had decided to pursue a career in theatre? Unfortunately we don't have the technology to slide into parallel worlds and explore alternative histories. However it turns out we do have the tools to simulate parallel realities and give decent answers to intriguing 'what if' questions. This talk will provide a gentle introduction to these tools, professionally known as Causal Inference.