Like light, sound travels in waves. Unlike light waves, however, sound waves are referred to as a mechanical wave.

In the case of sound waves, these mechanical waves come in the form of a vibrating wave that transports energy as it moves from one place to another.

This wave has to travel through what we call a medium, which in this case is through particles.

Let’s look at an example though, to make it a little clearer.

If you play a string of a guitar, the string vibrates. This initial vibration creates a chain reaction in the particles around it, in a way not too dissimilar to the ripples from a pebble dropped into a pond.

Each particle affected then transfers the vibrations onto those around it, transferring energy.

The further the sound wave travels, the weaker the vibration becomes.

This happens until the sound wave ceases to exist, due to a small amount of energy being lost in each transfer between particles.

So, for sound to travel, we need particles. These particles can make up a whole range of things including water, gas, liquids, or even solids.

Sound cannot travel through space though, as it is a vacuum. If you played a guitar in space, you wouldn’t hear it.

There are no particles in the enormous gaps of nothingness between cosmic bodies in space to vibrate, and thus the initial vibrations of the guitar string wouldn’t have anything to transfer to, and no one would ever hear it.

OK so wait, is space completely silent or not?

While space is more silent than you could ever imagine, it’s not completely devoid of sound.

Sound waves cannot travel through space, but there are some infinitesimally small regions where sound can exist, under very specific conditions.