In Space, Can Anyone Hear You Scream?

iStock/coffeekai
iStock/coffeekai

"In Space, No One Can Hear You Scream." That was the tagline for the movie Alien, Ridley Scott's 1979 sci-fi/horror masterpiece. Released two years earlier, Star Wars allowed us to hear plenty of things in space, like the whine of TIE fighter engines and the explosion of the Death Star.

So which movie is right? How does sound work in space?

Here on Earth, sound travels as mechanical waves transmitted through a solid, liquid or gas medium (like the air in a room, the water in a pool, or the walls in an apartment building). Pluck a guitar string and it vibrates. The vibration of the string pushes against the molecules of air around the string. Those air molecules, in turn, push against other air molecules, which push against still others, creating oscillations of pressure in the air: a sound wave.

Outer space (which, for our purposes here, we will define as the universe beyond Earth's atmosphere and between planets and other stellar bodies) makes a pretty terrible medium for mechanical waves. It's a vacuum, but not a perfect one. Sound can travel through it, but not very effectively. There's plenty of matter in space "“- stars, planets, asteroids, galaxies, cosmic dust, elemental atoms, etc. "“- and it's all separated by vast distances. Even at the densest parts, there's only a few hydrogen and helium atoms in a cubic meter. If you plucked a guitar string in outer space, it would still vibrate and scraps of matter like cosmic dust and gases might be able to propagate sound waves if you got enough of the matter together, but the sound be too weak for our not-that-sensitive ears to hear.

So, Alien has it right; while it's not strictly true that sound waves can't travel through space, it is true that humans would not be able to hear those sounds. Scream all you want, no one is hear you. There are some loopholes in what we'll call "Ridley's Law," though. Among the things you could hear in space are:

"¢ Anyone talking to you via radio. Radio waves can travel through space because they're electromagnetic, not mechanical, and can travel through a vacuum. Once the radio in your spaceship or spacesuit receives the signal, it converts the signal into sound, which travels through the air in your ship or helmet to your ear.

"¢ A bump on the head. If you're floating in space wearing a spacesuit and you hit your head on something (your ship, an asteroid, whatever), the sound waves resulting from the vibration of your helmet and the object you bumped would be able to travel through your helmet and the air inside it to your ear.

If you've got the right tools, you could also see sounds of a black hole. In 2002, NASA's Chandra X-ray Observatory detected a B-flat note coming from a black hole in the Perseus Galaxy Cluster, some 250 million light-years away. The note is 57 octaves below a piano's Middle C. That's far too low for us to hear. NASA didn't hear the note, either -- they saw it as ripples in the cosmic gas surrounding the hole, caused by the squeezing and heating of the gas by the gravitational pressure of the clump of galaxies packed together in the cluste. They determined the pitch by calculating how far apart the ripples were, and how fast they traveled.

Friday’s Best Amazon Deals Include Digital Projectors, Ugly Christmas Sweaters, and Speakers

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Amazon
As a recurring feature, our team combs the web and shares some amazing Amazon deals we’ve turned up. Here’s what caught our eye today, December 4. Mental Floss has affiliate relationships with certain retailers, including Amazon, and may receive a small percentage of any sale. But we only get commission on items you buy and don’t return, so we’re only happy if you’re happy. Good luck deal hunting!

What Are Sugar Plums?

Marten Bjork, Unsplash
Marten Bjork, Unsplash

Thanks to The Nutcracker and "'Twas the Night Before Christmas," sugar plums are a symbol of the holidays. But what are sugar plums, exactly? Like figgy pudding and yuletide, the phrase has become something people say (or sing) at Christmastime without knowing the original meaning. Before it was the subject of fairy dances and storybook dreams, a sugar plum was either a fruitless candy or a not-so-sweet euphemism.

According to The Atlantic, the sugar plums English-speakers ate from the 17th to the 19th century contained mostly sugar and no plums. They were made by pouring liquid sugar over a seed (usually a cardamom or caraway seed) or almond, allowing it to harden, and repeating the process. This candy-making technique was called panning, and it created layers of hard sugar shells. The final product was roughly the size and shape of a plum, which is how it came to be associated with the real fruit.

Before the days of candy factories, these confections could take several days to make. Their labor-intensive production made them a luxury good reserved for special occasions. This may explain how sugar plums got linked to the holidays, and why they were special enough to dance through children's heads on Christmas Eve.

The indulgent treat also became a synonym for anything desirable. This second meaning had taken on darker connotations by the 17th century. A 1608 definition from the Oxford English Dictionary describes a sugar plum as “something very pleasing or agreeable, esp. when given as a sop or bribe.” Having a "mouthful of sugar plums" wasn't necessarily a good thing, either. It meant you said sweet words that may have been insincere.

As true sugar plums have fallen out of fashion, demand for Christmas candy resembling the actual fruit has risen. You can now buy fancy candied plums and plum-flavored gummy candies for the holidays, but if you want something closer to the classic sugar plum, a Jordan almond is the more authentic choice.