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How far can sound travel through space, since it’s so empty? Is there an echo in space? – Jasmine, age 14, Everson, Washington
In space, no one can hear you scream.
You may have heard this saying. It’s the tagline from the famous 1979 science fiction movie “Alien.” It’s a scary thought, but is it true? The simple answer is yes, no one can hear you scream in space because there is no sound or echo in space.
I’m a professor of astronomy, which means I study space and how it works. Space is silent – for the most part.
How sound works
To understand why there’s no sound in space, first consider how sound works. Sound is a wave of energy that moves through a solid, a liquid or a gas.
Sound is a compression wave. The energy created when your vocal cords vibrate slightly compresses the air in your throat, and the compressed energy travels outward.
A good analogy for sound is a Slinky toy. If you stretch out a Slinky and push hard on one end, a compression wave travels down the Slinky.
Slinky toys can demonstrate how sound waves, a type of compression wave, work.
When you talk, your vocal cords vibrate. They jostle air molecules in your throat above your vocal cords, which in turn jostle or bump into their neighbors, causing a sound to come out of your mouth.
Sound moves through air the same way it moves through your throat. Air molecules near your mouth bump into their neighbors, which in turn bump into their neighbors, and the sound moves through the air. The sound wave travels quickly, about 760 miles per hour (1,223 kilometers per hour), which is faster than a commercial jet.
Sound waves are created when matter vibrates.
Space is a vacuum
So what about in space?
Space is a vacuum, which means it contains almost no matter. The word vacuum comes from the Latin word for empty.
Sound is carried by atoms and molecules. In space, with no atoms or molecules to carry a sound wave, there’s no sound. There’s nothing to get in sound’s way out in space, but there’s nothing to carry it, so it doesn’t travel at all. No sound also means no echo. An echo happens when a sound wave hits a hard, flat surface and bounces back in the direction it came from.
By the way, if you were caught in space outside your spacecraft with no spacesuit, the fact that no one could hear your cry for help is the least of your problems. Any air you still had in your lungs would expand because it was at higher pressure than the vacuum outside. Your lungs would rupture. In a mere 10 to 15 seconds, you’d be unconscious due to a lack of oxygen.
Sound in the solar system
Scientists have wondered how human…
