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? Beyond the remote potential for terrorists or a rogue state deploying a nuclear HEMP, most experts agree that another source of an EMP the sun is inevitable. Now, get a full presidential briefing to understand what could be the electronic Armageddon in one of the world's most wired countries.