How to Measure the Speed of Light With a Bar of Chocolate and Your Microwave

Caroline Delbert
·2-min read

From Popular Mechanics

  • You can use chocolate, cheese, or even marshmallows to microwave at the speed of light.

  • Your microwave has its wavelength listed somewhere, and it's easy to multiply the rest.

  • Also, you can still eat the food.

Sometimes science is super simple—and super tasty. A classic science experiment demonstrating how to use your microwave and a bar of chocolate to measure the speed of light is making the rounds, with easy-to-follow instructions for replicating the test at home.

🔬 You love badass science experiments. So do we. Let's play around together.

Chocolate at the speed of light sounds like a pandemic claustrophobia dream, but it’s the mechanism that propels this simple experiment. If you don’t like chocolate, you can also do the experiment with a slice of American cheese. (Also, the chocolate or cheese is still fine to eat after you zap and measure it.)

Here’s how the experiment works, courtesy of David Berardo, an astrophysics Ph.D. student at the Massachusetts Institute of Technology. First, you remove the turntable from the microwave so you can put in a plate that will stand still while the microwave runs. Then you put in a bar of chocolate or slice of cheese for about 20 seconds, enough to see the effects begin to take shape.

What you’ll see is a specific pattern of melting that shows the wavelength of the microwaves that power your oven. And when you measure the wavelength and multiply it out by the microwave frequency, you’ll end up with a surprisingly close approximation of the speed of light.

Almost all microwaves have the frequency listed either on the back or inside the door. Since waves bounce inside the microwave, the numbers aren’t exact—but this isn’t the Fermi Lab, either. It’s for fun, and you’re probably stuck at home. Open a Hershey bar or a Kraft Single and do a little science.

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Interesting Engineering reports that the experiment dates back to a 2004 science education conference. (For s’more sake of argument, a physics teachers website lists it at 1997 at the latest, based on a published example using marshmallows.)

The inventor of the microwave probably understood on some level that this was possible, because they also decided at some point that the device needed a turntable to evenly distribute waves of heat, right?

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