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Caitlin: If you're hearing me talking right now, congratulations, that means you are not adrift in the cold, near-vacuum of space. Sound waves can't travel through space, so if you were floating around out there, they'd never reach your ears, no matter what those sci-fi movies make it sound like, you'd never hear any ships exploding. But audible or not, the universe is making noise, and scientists have developed ways of eavesdropping on it. 

When we say 'sound', we're referring to particles that vibrate in a particular pattern. Those vibrations create a longitudinal wave which just means that they move back and forth, or oscillate, in the same direction they're traveling. The wave continues when the moving particles knock into the ones next to them, which is why sound waves have to travel through a medium, like air or water.  Basically, there need to be particles nearby to keep the vibrations, and therefore the sound, going. 

In space, things are a little different. It's not completely empty out there, even in interstellar space, but it's so close to a vacuum that there aren't enough particles to pass along the vibrations of soundwaves. But there are other types of waves moving through the universe, and all it takes to listen in is the right equipment.

Electromagnetic waves are like longitudinal waves in the sense that they oscillate in a predictable pattern. But since they're traveling as changes in electric and magnetic fields instead of as moving particles, electromagnetic waves don't need a medium to travel through. Still, just like sound, electromagnetic waves have a frequency, which is the measure of how often they oscillate over time, and when they travel through plasma, the ionized gas and dust that's spread through space, they affect its electric and magnetic fields. All this makes electromagnetic waves extremely useful, because we can pick up on the changes in those fields, and in a way, scientists can use them to actually listen to space. 

In 2013, a NASA probe was able to interpret waves in interstellar plasma, a sound that humans could hear. In March 2012, the sun had a tantrum in the form of a massive solar flare. This produced a kind of electromagnetic shockwave, and about a year later, it hit the plasma surrounding Voyager 1, the space probe that spent nearly 40 years leaving the solar system. As the electromagnetic waves resonated through the plasma, they were picked up by Voyager's sensors. No human could hear these plasma waves themselves, but they did vibrate at frequencies that fall within the range of human hearing, which is between 20 and 20,000 hertz, or oscillations per second. Voyager 1 recorded the vibrations and sent them back to Earth, where physicists used the data to figure out the density of the plasma the probe was traveling through. Turns out the density matched what was expected for interstellar space.  Voyager 1 had officially left the solar system, and when they reproduced the frequency of the plasma out there, as if it had traveled through the air, it sounded like this (plays audio clip). 

Another famous addition to our universe's soundtrack came from our old friend, the comet 67P/Churyumov-Gerasimenko. In November of 2014, the European Space Agency's Rosetta Spacecraft detected some strange vibrations. Like the interstellar activity that Voyager 1 observed, these sounds wouldn't have been audible without a bit of tweaking, since, at 40-50 mHz, they fell far below the range of human hearing.  Scientists still aren't sure what exactly caused those vibrations, but they think it was the comet releasing particles into its coma, the plasma atmosphere that surrounds it. By increasing the frequencies of the plasma waves by 10,000 times, we're able to listen to a scaled-up version of comet 67P belting them out. 

So those whooshing sounds that spaceships make in movies are just dramatic sound effects for the entertainment value of us Earthlings, because no medium in space means no sound, but we don't need air, we've got science! Thanks for watching this episode of SciShow Space, and especially thank you to our patrons on Patreon, who help make this show possible.  If you wanna help support this content and receive rewards like Google Hangouts with the hosts and crew, go to Patreon.com/SciShow to learn more, and don't forget to go to YouTube.com/SciShowSpace and subscribe.

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