Based on Richard Muller's book, Physics for Future Presidents, National Geographic investigates the science behind the dangers of a high-altitude electromagnetic pulse, or HEMP. Picture an instantaneous deathblow to the vital engines that power our society, delivered by a nuclear weapon designed not to kill humans but to attack electronics. What could happen if an electromagnetic pulse surged to earth, crippling every aspect of modern society's infrastructure, including our especially vulnerable electrical grid? (50 minutes)