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Movies like Predator reveal how useful thermal imaging goggles can be, but why do hot objects give off infrared radiation to begin with?

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Thanks to Skillshare for supporting this episode, and this whole week, of SciShow. [♪ INTRO].

Let’s say you’re Arnold Schwarzenegger’s character in the new blockbuster. Predator Terminates Expendables into Oblivion…17.

As usual, you’re chasing bad guys all over the battlefield with absurdly huge guns, all in the dark. How do you pull it off? Well, for pitch-black situations, you could snag some thermal imaging goggles.

These gadgets show hotter and colder areas, revealing any people, animals, and cars hiding in the deepest shadows. How they work is pretty simple: Heat is released as infrared radiation that the goggles pick up, then different amounts of infrared are translated into different visible colors. But the bigger question is, why do we associate infrared and heat in the first place?

Why don’t hot objects just give off something like radio waves, or any other kind of radiation? Turns out, it’s kind of a coincidence. Heat energy is about molecules vibrating and wiggling and bouncing off each other.

Infrared, on the other hand, is a totally different kind of thing. It’s not about molecules at all. Instead, infrared is actually a type of electromagnetic, or EM radiation.

Like visible light, radio waves, and X-rays, it’s just a bunch of photons carrying around energy. And it seems like that shouldn’t tell you anything about temperature. So why do hot, vibrating molecules give off radiation at all?

And why specifically infrared? It has to do with something called black-body radiation. This is the EM radiation given off by every object above absolute zero, that’s objects with any heat energy at all, including you, me, and aliens in the latest Predator movie.

It happens because, when heated molecules wiggle, they jerk around any charged particles inside them, stuff like electrons. And charged particles being pushed or tugged is actually what produces EM radiation in the first place. So, thanks to your moving molecules, you’re glowing from heat like an incandescent light bulb!

Clearly, though, you don’t glow much in the visible part of the spectrum. That’s because how much radiation an object emits at which wavelengths depends on temperature. And this is where infrared starts to show up.

All objects give off all wavelengths of radiation, but the hotter an object is, the brighter and higher-frequency most of that radiation is. At the temperatures you encounter in normal life, most objects primarily emit infrared. That’s why thermal goggles are designed to detect it and not, say, radio waves.

But if we heated you up to the same temperature as a light bulb, you’d start to give off a lot of yellow light, too! Although you probably wouldn’t enjoy the experience. Meanwhile, if you were in the coldest regions of space, you’d need microwave vision to see whatever heat there was.

And on the blazing edge of a black hole, you’d want X-ray goggles. So the connection we make between infrared and heat is kind of a happy accident, just based on temperatures here on Earth. Let’s just hope you don’t need to know that to survive an alien invasion.

So, we learned that one way we can see humans glow is in infrared, but another way we can highlight our glowing selves is through stories! This week we’re highlighting classes on SkillShare that we think you’ll like. This one, taught by Keith Yamashita, is called Storytelling For Leaders:.

How To Craft Stories That Matter. In it, he talks about the components of a great story, story archetypes, and invites you to work through the process of creating your own story, using some worksheets and a sort of flashcard activity to get you thinking about your story in a new way! I always enjoy honing my storytelling skills.

And the information in this class can be applied to any story, whether it’s fiction or non-fiction. Thanks to Skillshare for sponsoring this episode. Right now you can get two months of unlimited access for free, and help support SciShow, by following the link in the description. [♪ OUTRO].