Exordia (2024) by Seth Dickinson is a fun romp on trolley problems if your idea of fun includes "nuke Kurdistan or else we nuke the world". Obama is president, and an alien appears in Central Park to drag some broken people into a battle over an artifact that can change the universe. These aliens have actual Original Sin, and visibly so. Humans freak out at the alien wrongness, a metaphysical brand that shows the entire alien race is doomed from birth to go to a literal hell when t…