In the stew of false information and conspiracy theories that swirls online, perhaps no idea is as flummoxing as the belief in a flat Earth. Flat-Earthers believe that the Earth is a flat disc ringed by an ice wall. All those elegant models of a round Earth that perfectly explain seasons, eclipses, sunrises and sunsets? Lies and cover-ups, they say. Pictures of the round Earth from space? Government conspiracies. The fact that you can see ships disappearing hull-first over the curve of the horizon with your own eyes? Well, flat-Earthers claim to see something different. It's been a big publicity...