The microwave oven was invented after a radar engineer noticed the chocolate bar in his pocket had melted.
In 1945, Percy Spencer was testing a magnetron, the tube that generates radar waves, when the snack in his pocket turned to goo. He then tried popcorn, which popped, and an egg, which exploded.
Why is this true?
Microwaves make water molecules in food vibrate, and the friction heats it from the inside. The first commercial microwave oven in 1947 was nearly two metres tall and weighed 340 kilograms.
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More about inventions
Most inventions arrive by accident, in the wrong order, or decades before anyone finds a use for them. Microwaves, sticky notes, safety glass and vulcanised rubber all started as mistakes or side effects. The facts here trace how the thing actually came about, note who noticed the accident and why it mattered, and point at a source so you can follow the full story if it hooks you.