In 1945, engineer Percy Spencer was working on a radar set at Raytheon. He noticed its microwaves, a kind of energy wave, melting a candy bar in his pocket.
So he tried cooking with them on purpose. Popcorn came first. Next came an egg, which exploded in an experimenter's face.
In 1947, Raytheon built the first microwave oven for sale. It stood almost 1.8 meters (6 feet) tall and weighed 340 kilograms (750 pounds).