Asked by: Sarah Green, Newcastle
To create a sound, we have to set matter - whether it's a gas like air, a liquid or even a solid material - in regular motion, creating a wave of specific frequencies, which we hear as a sound of a particular pitch. Setting matter in motion like this obviously requires energy, which will inevitably become dissipated as the waves pass through the air and more solid materials. Eventually the motion ceases entirely and no more sound can be heard - producing silence.
Robert is a science writer and visiting professor of science at Aston University.