Sex Can time travelers go back in time and have sex with themselves? Astrophysicists investigate. Thom Dunn
brain teasers Saturday morning mind-benders: "Newcomb's Problem" and "Parfit's Hitchhiker" dilemma Mark Frauenfelder
game theory How "God Makes God" is a 1993 CD-ROM about probability, game theory, genetic algorithms, and evolutionary strategies Mark Frauenfelder
mathematics New research: There's a 50-50 chance we're living in a simulation and here's how to find out David Pescovitz
late stage capitalism The paradox of good government: the best stuff works well and is thus unnoticeable (and therefore easy to sell off) Cory Doctorow
optical illusions The Playful Eye is a virtual feast of games and visual tricks gathered from around the world Kevin Kelly