On Long Bets, a website where prognosticators test their mettle by playing for real (or at least proceeds-donated-to-charity) stakes, there is an open bet between British astrophysicist Martin Rees, a noted worrier over apocalyptic possibilities, and Harvard University’s Steven Pinker, famous for his vaulting optimism.

For Rees to win, the following prediction must be vindicated: “A bioterror or bioerror will lead to one million casualties in a single event within a six-month period starting no later than Dec 31, 2020.”