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Why Can't You Put Metal in the Microwave?

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Daven Hiskey runs the wildly popular interesting fact website Today I Found Out. To subscribe to his “Daily Knowledge” newsletter, click here.

We've all heard that it's not safe to put metal in the microwave. But the fact of the matter is, we often put metals in the microwave—like when we heat up a Hot Pocket, for example. Its pouch has a thin layer of aluminum lining that is designed to absorb the microwaves and heat up a bit to brown the outside of the Hot Pocket.

Plus, the inside walls of your microwave oven are made of metal. This forms a Faraday cage, which traps the microwaves inside the box, so that they cook the food and not things around the microwave oven (like you). The microwave window also has metal mesh lining it. The holes in this mesh are smaller than the wavelengths of the electromagnetic radiation your microwave is producing, which keeps the waves from passing through the holes. Visible light, however, is comprised of much smaller wavelengths, so that form of radiated energy passes through the holes just fine, allowing you to see inside your microwave while it’s running without getting cooked yourself.

So if the inside of your microwave is lined with metal, and certain food products have containers that contain metal, why does your microwave manual warn you not to put metal in the microwave?

How Microwave Ovens Work

At its core, a microwave oven is a pretty simple device: a magnetron hooked up to a high voltage source. This magnetron directs microwaves into the metal box where your food is cooked; the waves bounce around inside the microwave until they are absorbed via dielectric loss in various molecules, which results in those molecules heating up. Substances that work well here are things such as water, ceramics, and certain polymers, which all end up converting microwave energy into heat quite effectively.

Metals, on the other hand, are packed with electrons that can move freely, and are therefore great conductors of electricity. When microwaves hit the metal you put in your microwave, free electrons on the metallic surface end up moving from side to side very rapidly. This, in turn, prevents the electric wave from entering the metal, and the waves end up being reflected instead.

More Metal, More Problems

When microwaves are reflected instead of being absorbed, it can potentially create a sufficient charge density that the electrical potential in the metal object exceeds the dielectric breakdown of air. When this happens, it will result in arcing inside your microwave, from that metal to another electrical conductor with lower potential (often the wall of the microwave). In extreme cases, these electrical sparks can end up burning small holes in the metal wall. The sparks can also end up burning out the magnetron in your microwave oven or, in modern microwaves, can generate a surge that ends up damaging sensitive microelectronics, possibly killing your microwave or making it unsafe to use.

Another way putting metal in the microwave can kill the magnetron is when enough of the generated microwaves don’t get absorbed, which might happen if the food is wrapped in aluminum foil or mostly enclosed in a metal container. If the energy isn't absorbed, it has nowhere to go but back to the magnetron to damage it—which, again, can render your microwave useless.

On a more mundane level, putting your food in the microwave with something like a regular spoon or a metal plate means that it probably won't get cooked properly. In general, putting metal in the microwave is unsafe—not because you are at risk of bodily harm (though in extreme cases a fire might be started in your microwave)—but because it could potentially damage your microwave. Just a little something to consider when you're reheating your holiday leftovers.

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Pop Culture
The Sweet Surprise Reunion Mr. Rogers Never Saw Coming
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Family Communications Inc./Getty Images

For more than 30 years, legendary children’s show host Fred Rogers used his PBS series Mister Rogers’ Neighborhood to educate his young viewers on concepts like empathy, sharing, and grief. As a result, he won just about every television award he was eligible for, some of them many times over.

Rogers was gracious in accepting each, but according to those who were close to the host, one honor in particular stood out. It was March 11, 1999, and Rogers was being inducted into the Television Academy Hall of Fame, an offshoot of the Emmy Awards. Just before being called to the stage, out came a surprise.

The man responsible for the elation on Rogers’s face was Jeff Erlanger, a 29-year-old from Madison, Wisconsin who became a quadriplegic at a young age after undergoing spinal surgery to remove a tumor. Rogers was surprised because Erlanger had appeared on his show nearly 20 years prior in 1980 to help kids understand how people with physical challenges adapt to life’s challenges. Here's his first encounter with the host:

Reunited on stage after two decades, Erlanger referred to the song, “It’s You I Like,” which the two sang during their initial meeting. “On behalf of millions of children and grown-ups,” Erlanger said, “it’s you I like.” The audience, including a visibly moved Candice Bergen, rose to their feet to give both men a standing ovation.

Following Erlanger’s death in 2007, Hedda Sharapan, an employee with Rogers’s production company, called their poignant scene “authentic” and “unscripted,” and that Rogers often pointed to it as his favorite moment from the series.

Near the end of the original segment in 1980, as Erlanger drives his wheelchair off-camera, Rogers waves goodbye and offers a departing message: “I hope you’ll come back to visit again.”

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© 2002 Twentieth Century Fox
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entertainment
20 Things You Might Not Have Known About Firefly
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© 2002 Twentieth Century Fox

As any diehard fan will be quick to tell you, Firefly's run was far, far too short. Despite its truncated run, the show still offers a wealth of fun facts and hidden Easter eggs. On the 15th anniversary of the series' premiere, we're looking back at the sci-fi series that kickstarted a Browncoat revolution.

1. A CIVIL WAR NOVEL INSPIRED THE FIREFLY UNIVERSE.

The Pulitzer Prize-winning novel The Killer Angels from author Michael Shaara was Joss Whedon’s inspiration for creating Firefly. It follows Union and Confederate soldiers during four days at the Battle of Gettysburg during the American Civil War. Whedon modeled the series and world on the Reconstruction Era, but set in the future.

2. ORIGINALLY, THE SERENITY CREW INCLUDED JUST FIVE MEMBERS.

When Whedon first developed Firefly, he wanted Serenity to only have five crew members. However, throughout development and casting, Whedon increased the cast from five to nine.

3. REBECCA GAYHEART WAS ORIGINALLY CAST TO PLAY INARA.

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Before Morena Baccarin was cast as Inara Serra, Rebecca Gayheart landed the role—but she was fired after one day of shooting because she lacked chemistry with the rest of the cast. Baccarin was cast two days later and started shooting that day.

4. NEIL PATRICK HARRIS WAS ALMOST DR. SIMON TAM.

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Before it went to Sean Maher, Neil Patrick Harris auditioned for the role of Dr. Simon Tam.

5. JOSS WHEDON WROTE THE THEME SONG.

Whedon wrote the lyrics and music for Firefly’s opening theme song, “The Ballad of Serenity.”

6. STAR WARS SPACECRAFT APPEAR IN FIREFLY.

Star Wars was a big influence on Whedon. Captain Malcolm Reynolds somewhat resembles Han Solo, while Whedon used the Millennium Falcon as inspiration to create Serenity. In fact, you can spot a few spacecraft from George Lucas's magnum opus on the show.

When Inara’s shuttle docks with Serenity in the pilot episode, an Imperial Shuttle can be found flying in the background. In the episode “Shindig,” you can see a Starlight Intruder as the crew lands on the planet Persephone.

7. HAN SOLO FROZEN IN CARBONITE POPS UP THROUGHOUT FIREFLY.

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Nathan Fillion is a big Han Solo fan, so the Firefly prop department made a 12-inch replica of Han Solo encased in Carbonite for the Canadian-born actor. You can see the prop in the background in a number of scenes.

8. ALIEN'S WEYLAND-YUTANI CORPORATION MADE AN APPEARANCE.

In Firefly’s pilot episode, the opening scene features the legendary Battle of Serenity Valley between the Browncoats and The Union of Allied Planets. Captain Malcolm Reynolds takes control of a cannon with a Weyland-Yutani logo inside of its display. Weyland-Yutani is the large conglomerate corporation in the Alien film franchise. (Whedon wrote Alien: Resurrection in 1997.)

9. ZAC EFRON'S ACTING DEBUT WAS ON FIREFLY.

A 13-year-old Zac Efron made his acting debut in the episode “Safe” in 2002. He played Young Simon in a flashback.

10. CAPTAIN MALCOLM REYNOLDS'S HORSE IS A WESTERN TROPE.

At its core, Firefly is a sci-fi western—and Malcolm Reynolds rides the same horse on every planet (it's named Fred).

11. FOX AIRED FIREFLY'S EPISODES OUT OF ORDER.

Fox didn’t feel Firefly’s two-hour pilot episode was strong enough to air as its first episode. Instead, “The Train Job” was broadcast first because it featured more action and excitement. The network continued to cherry-pick episodes based on broad appeal rather than story consistency, and eventually aired the pilot as the show’s final episode.

12. THE ALLIANCE'S ORIGINS ARE AMERICAN AND CHINESE.

The full name of The Alliance is The Anglo-Sino Alliance. Whedon envisioned The Alliance as a merger of American and Chinese government and corporate superpowers. The Union of Allied Planets’ flag is a blending of the American and Chinese national flags.

13. THE SERENITY LOUNGE SERVED AS AN ACTUAL LOUNGE.

Between set-ups and shots, the cast would hang out in the lounge on the Serenity set rather than trailers or green rooms.

14. INARA SERRA'S NAME IS MESOPOTAMIAN.

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Inara Serra is named after the Mesopotamian Hittite goddess, the protector of all wild animals.

15. THE CHARACTERS SWORE (JUST NOT IN ENGLISH).

The Firefly universe is a mixture of American and Chinese culture, which made it easy for writers to get around censors by having characters swear in Chinese.

16. THE UNIFORMS ARE RECYCLED FROM STARSHIP TROOPERS.

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The uniforms for Alliance officers and soldiers were the costumes from the 1997 science fiction film Starship Troopers. The same costumes were repurposed again for the Starship Troopers sequel.

17. "SUMMER!" MEANS SOMEONE MESSED UP.

Every time a cast member flubbed one of his or her lines, they would yell Summer Glau’s name. This was a running gag among the cast after Glau forgot her lines in the episode “Objects In Space.”

18. THE SERENITY SPACESHIP WAS BUILT TO SCALE.

The interior of Serenity was built entirely to scale; rooms and sections were completely contiguous. The ship’s interior was split into two stages, one for the upper deck and one for the lower. Whedon showed off the Firefly set in one long take to open the Serenity movie.

19. "THE MESSAGE" SHOULD HAVE BEEN THE SHOW'S FAREWELL.

Although “The Message” was the twelfth episode, it was the last episode filmed during Firefly’s short run. Composer Greg Edmonson wrote a piece of music for a funeral scene in the episode, which served as a final farewell to the show. Sadly, it was one of three episodes (the other two were “Trash” and “Heart of Gold”) that didn’t air during Firefly’s original broadcast run on Fox.

20. FIREFLY AND SERENITY WERE SENT TO THE INTERNATIONAL SPACE STATION.

American Astronaut Steven Ray Swanson is a big fan of Firefly, so when he was sent to the International Space Station for his first mission (STS-117) in 2007, he brought DVD copies of Firefly and its feature film Serenity aboard with him. The DVDs are now a permanent part of the space station’s library.

This post originally appeared in 2014.

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