Earlier this month, two fan conventions came to London: Nine Worlds and the World Science Fiction Convention, commonly know as Worldcon. Worldcon is in its 72nd year, a huge old dinosaur (or perhaps an aging dragon) of science-fiction fandom. This year more than 10,000 people paid for memberships, which included entrance to the annual Hugo Awards. The official guests of honor were revered science-fiction and fantasy authors, editors, and illustrators, all of whom were in their 60s and 70s. Nine Worlds was smaller, younger, and catered to a more varied crowd including comics, TV, and fanfic followers. But since both...