The Silent Vacuum Where Sound Waves Die

Outer space is silent because sound is a mechanical wave that requires a medium to travel through. On Earth, sound moves by bumping air molecules into one another like a line of falling dominoes. In the vacuum of space, those dominoes don't exist.

Because the distance between atoms in the void is so massive, a vibration has nothing to push against. If a star exploded right next to you, you wouldn't hear a roar; you would only see a blinding flash of light. Light, unlike sound, is an electromagnetic wave and doesn't need atoms to hitch a ride on.

However, this doesn't mean space is empty. It is filled with gas and dust, but the density is too low for our ears to detect. In some massive gas clouds, sound waves can actually exist, but their frequency is so low—one vibration every few million years—that no human could ever perceive them.

Astronauts solve this by using radio waves to talk. Radio waves are a form of light, allowing them to jump across the vacuum. When they speak, their electronics turn the sound of their voice into light, beam it to a teammate's helmet, and turn it back into air vibrations inside the suit.

If two astronauts touched their glass helmets together, they could actually hear each other speak. The sound would travel from the air inside one suit, through the solid glass, and into the air of the second suit, bypassing the silence of the vacuum entirely.