The most exciting part about scientific progress is that you never know where it will lead. Scientists and inventors tinker and experiment with a goal in mind, but along the way, all sorts of things can be learned. Here are five of the most important things that were discovered by accident.


Photo of a hand pressing buttons on a microwave
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This common household appliance originated in a radar testing lab in 1945. Raytheon engineer Percy Spencer was testing magnetrons, microwave-emitting devices that were a part of early radar systems, when he noticed that a chocolate bar in his pocket was melting.

Spencer soon realized that the candy bar was being cooked by the microwaves produced by the magnetrons and realized the potential for the device in food preparation. Raytheon filed a patent for the microwave cooking process that same year, although development of the device took longer – the microwave oven wasn’t widely available to consumers until 1967.


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One of the most important advances in modern medicine happened almost entirely by chance. In 1928, Scottish scientist Alexander Fleming was studying staph infections by cultivating the bacterium staphylococcus in the laboratory of a London hospital when he noticed something unusual. He had left a petri dish with the bacteria exposed to open air in the lab overnight, expecting it to grow.

However, instead of the bacteria expanding, they had been overtaken by a mold. Fleming soon realized the mold had restricted the growth of the bacteria. He named the mold penicillin and laid the groundwork for antibacterial medicine.


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The discovery of this ubiquitous artificial sweetener was a happy accident from Constantine Fehlberg’s research into coal tar. The chemist’s work at John Hopkins University put him in close contact with the ortho-sulfobenzoic acid imide, and one night he took a break from his work to have his dinner, only to find that his dinner tasted sweeter than usual.

Fehlberg isolated the chemical that was causing the effect and soon set up a company to mass produce the sweetener under the name Saccharin. Sales were slow when Fehlberg introduced the product in 1879, but during the sugar shortages brought on during the Second World War, the artificial sweeter became ubiquitous across America.


Photo of an x-ray of a pacemaker in a human chest
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The pacemaker, a life saving device that helps irregular heartbeats, was discovered by Wilson Greatbatch while he was working on a much less ambitious project. Greatbatch was attempting to fine tune a simple heart listening device when he selected the wrong size resistor to finalize the circuit board of the device.

After struggling to make the resistor fit, he noticed that once installed, it emitted an electronic pulse that was sent out for 1.8 milliseconds before pausing for a full second – just like the human heart. He began efforts to make the device as small as possible, and two years later, in 1958, the first pacemaker was implanted in a living test subject.


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In 1985, Wilhelm Röntgen was working with cathode rays when he noticed a strange phenomenon. He had a piece of fluorescent cardboard propped up in his lab, across the room from the cathode tubes and obscured by a screen that prevented natural light from reaching the two.

However, he noticed that the cardboard had begun to glow. He soon deduced that x-rays had the ability to pass through solid objects and could be used to produce images of hidden objects – such as our bones.

The list goes on

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The list of accidental discoveries doesn’t stop there. Post-It-Notes, Slinkies, and Krazy Glue were all stumbled upon in the pursuit of different discoveries. In our world of constant innovation, you never know what today’s inventors will stumble over next.