In 1945, Percy Spencer noticed something unusual while working on radar equipment: the candy bar in his pocket had melted. The engineer began experimenting with popcorn and an egg, eventually setting him on the path to developing the microwave oven.

In 1945, engineer Percy Spencer was working with radar equipment at Raytheon when he noticed something strange. A candy bar he had been carrying in his pocket had melted. Spencer suspected that the magnetron he was working with might have caused it.

The magnetron was an important part of radar technology, producing microwave energy that could be used to detect objects. Spencer wondered whether that same energy could also heat food. Instead of dismissing the melted candy as an odd accident, he decided to investigate.

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Spencer tested the idea with popcorn

Spencer placed popcorn kernels near the equipment and watched what happened. The kernels began to heat up and pop. That gave him a much stronger clue that the microwave energy was responsible for the heating.

He conducted another experiment using an egg. When the egg was exposed to the microwave energy, pressure built up inside it until it eventually exploded.

The experiments suggested that the energy from the magnetron could heat food rapidly. What began as a melted candy bar was starting to look like something much bigger.

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The radar technology behind the discovery

The story of the microwave oven is closely connected to World War II and the development of radar.

Magnetrons were essential components in radar systems because they generated high-frequency radio waves. These waves could be transmitted and reflected back from objects, helping radar operators detect aircraft and ships.

Spencer was already deeply familiar with the technology. His work at Raytheon involved improving the production of magnetrons, giving him the technical knowledge to understand what might have caused the candy bar to melt.

The discovery wasn't simply about accidentally putting candy near a machine. Spencer recognized an unusual effect and then designed experiments to understand it.

From experiment to microwave oven

Once Spencer established that microwave energy could heat food, Raytheon began developing a practical way to use the discovery. The company built a metal enclosure around the microwave-producing equipment, allowing the energy to be contained and used for heating food.

Spencer and Raytheon eventually patented the process. But the first microwave ovens were a long way from the compact appliances found in kitchens today.

The first microwave was huge

The first commercial microwave oven, known as the Radarange, appeared in 1947. It was enormous compared with modern microwave ovens. Early models were around 6 feet tall and weighed hundreds of pounds. They were also extremely expensive.

That meant the technology wasn't immediately suitable for the average household. Instead, early microwave ovens were more practical for commercial settings where speed and convenience could justify their cost.

Over the following years, engineers worked on making the machines smaller, more affordable and easier to operate.

When microwaves entered homes

The microwave gradually moved toward the household kitchen as the technology became more practical. One important milestone came in 1967, when Amana introduced a countertop Radarange priced at $495.

It was still expensive, but it was dramatically more convenient than the giant commercial machines that came before it.

As prices fell and consumers became more familiar with the technology, microwave ovens began appearing in more homes. The appliance eventually became a staple for reheating leftovers, preparing frozen meals and making quick snacks.

A surprising invention born from radar

The history of the microwave oven is unusual because its roots have little to do with traditional cooking. The technology came from radar research, while the crucial clue came from something as ordinary as a candy bar.

Percy Spencer's curiosity turned that unexpected moment into a series of experiments. Popcorn helped demonstrate the heating effect, while the exploding egg provided another striking piece of evidence.

From there, engineers transformed the discovery into a machine that could deliberately use microwave energy to heat food. Today, millions of people use microwave ovens without giving much thought to how they work.