In April 1978, MIT professor Amar Bose was flying home to Boston from Switzerland. But when he tried to listen to music through the airline’s headphones, he couldn’t hear a darned thing. He spent the rest of the flight doing acoustical math—and sketching out an idea for headphones that literally subtracted background noise from what you hear. Today, noise-canceling headphones are everywhere. But the revolution began with Amar Bose’s airplane sketches—and the 22-year, $50 million journey that led them to the ears on your head.