On a warm day in mid-July, a roomful of Nobel laureates and nuclear security experts, some 80 pairs of eyes, gaze out of the expansive windows of a 10th floor University of Chicago conference room, imagining their deaths by nuclear explosion. A presenter directs the group’s attention past the trees and gothic buildings of campus, over the apartment buildings in Hyde Park, and out to the Chicago skyline, hazy with wildfire smoke from Canada. He points out which neighborhoods would vanish in blasts of varying size, estimating casualties, injuries, and radiation effects.