First World, Third World, East, West, North and South; every few years economists come up with yet another supposedly more acceptable way of slicing humanity into manageable chunks. Mostly these great divides are riven by wealth; sometimes (RIP Second World) by ideology.

But I think it’s time to name a new divide, a more fundamental, more puzzling one — a split between worlds that will define the 21st century much as the Iron Curtain defined the 20th.