A melted chocolate bar in someone's pocket gave us the microwave.

In 1945, Percy Spencer was a self-taught engineer at Raytheon, walking past an active radar magnetron — a vacuum tube that generates microwave radiation — when he noticed something odd. The chocolate bar in his pocket had turned into a gooey mess.

Spencer didn't panic. He experimented. He pointed the magnetron at popcorn kernels first; they popped. Then at an egg, which exploded. Then, with the calm curiosity of a man who had taught himself electrical engineering from library books, he started building the first prototype oven around the magnetron.

Raytheon filed the patent in 1945. The first commercial microwave oven, the Radarange, stood nearly six feet tall, weighed 750 pounds, and cost around $5,000 — roughly $75,000 today. It was marketed to restaurants and industrial kitchens, not households.

The countertop version didn't reach ordinary American homes until the late 1960s and early 1970s, after Raytheon acquired Amana Refrigeration. The machine that now reheats leftovers in under two minutes began its life as a piece of Cold War radar infrastructure.