Bill, a loyal MR reader, asks:
A freak solar event "sterilizes" the half of the planet (people, animals, etc) facing the sun. What happens?
Putting aside, the "which half" question, I would predict the collapse of many fiat currencies and the immediate insolvency of most financial institutions. Who could meet all those margin calls? Unemployment would exceed 20 percent and martial law would be declared, food rationing and guys with rifles on street corners. The affected countries would take in larger numbers of immigrants, especially young immigrants from poorer countries, to keep their societies going and to use and maintain the still-standing capital stock. Many of those immigrants might be better off in the longer run, especially if they could internalize the norms of the host country by the time the original inhabitants perished. If you let me "cheat," I'll postulate that genetic engineering is used to perpetuate the genes of the original inhabitants.
If a poor country were hit by this blast the eventual result probably would be mass starvation. There is a chance that social order would collapse across the entire globe, due mostly to contagion effects, multiple equilibria, and bad expectations.
To some of you these mental exercises may seem silly. Indeed they are silly. But what's wrong with silly? Such questions get at the stability of social order, the sources of that stability, and the general importance of demography and intergenerational relations. Those are all topics we don't think enough about. Because we're not silly enough.