Why Can’t We Hear In Space?

A drawing of an astronaut floating in space.

In the past, perhaps during your science class, you might have heard that it’s not possible to hear or talk to each other in space. Well, believe it or not, that statement is actually true because space is a silent vacuum.

At first, all of this may seem like complete nonsense, but, in reality, there’s a pretty good reason for why this is. The way sound is produced and travels is through a series of vibrations. For example, when you talk, your vocal cords shake and vibrate in a specific way. This shaking and vibration moves the air around the vocal cords, causing air particles to then bump into each other, which passes the vibration forward. When these vibrations reach the listener’s ears, it shakes the eardrums, and your brain interprets that as hearing something.

If you haven’t caught on already, to produce sound, there always needs to be something to carry vibrations. This "something" is usually referred to as a medium, and the most common sound medium on Earth, at least for humans, is air.

Water does the job too if you’re underwater, and solids like wood or metal work just as well. Without one of these mediums, however, those vibrations don’t travel anywhere, and if they don’t travel, there’s nothing to hear. Space doesn’t have a medium the way Earth does. It’s mostly empty out there, and it’s basically just a vacuum where almost no particles hang around. Between all those stars and planets, you won’t find air or water or anything solid enough to move vibrations along. Sure, it’s not totally empty—tiny bits of dust and gas float here and there, and sometimes a stray atom pops up. But those particles sit so far apart that they don’t bump into each other like air molecules do when you snap your fingers. Because they’re spread out like that, vibrations don’t get passed forward, and no sound is made.

Now, let’s get into what space is actually like. Scientists call it a vacuum, which just means it’s got hardly any stuff in it. On Earth, air pushes down on us all the time, and we measure that push at about 14.7 pounds per square inch at sea level. Out in space, that push drops to almost nothing. That’s because, as mentioned before, there aren’t many particles in space, at least outside of those found on celestial objects. Earth’s air packs billions of molecules into every little space, all set out to carry vibrations. Space, on the other hand, might have a few particles per cubic meter, if you’re lucky. With so little to work with, sound isn’t really able to travel.

You might wonder about the Sun or stars. They’re massive and busy, so shouldn’t they make some noise? Well, they do. Inside the Sun, gases swirl and crash around, creating what would be sound if something carried it. Scientists study those vibrations with special gear, but they don’t hear them like we hear a car horn. Out in space, a vacuum sits in between us and the Sun, so those vibrations don’t come to us as noise.

The speed of sound somewhat ties into this too. On Earth, sound moves at about 343 meters per second through air. In water, it’s faster, around 1,480 meters per second, because water’s thicker with particles. In space, with no medium, there’s no speed to talk about—it doesn’t move at all. Simply put, it’s all about the particles. When they’re packed tight, like in water, vibrations get pushed along quick. Space has so few particles that the whole process shuts down before it starts.

The silence of space changes how we explore it. For instance, we use telescopes because they grab light, and light, unlike sound, moves through a vacuum just fine. Sound can only be found in places with a medium. That’s why we depend on pictures and other data to learn about the universe. A supernova might brighten the sky, but it won’t rumble over to us. The energy’s out there, just not in a way we can hear.