In the blink of an eye, electromagnetic bombs could throw civilization back 200 years. And terrorists can build them for $400. BY JIM WILSON Lead illustration by Edwin Herder The next Pearl Harbor will not announce itself with a searing flash of nuclear light or with the plaintive wails of those dying of Ebola or its genetically engineered twin. You will hear a sharp crack in the distance. By the time you mistakenly identify this sound as an innocent clap of thunder, the civilized world will have become unhinged. Fluorescent lights and television sets will glow eerily bright, despite being...