Part of the show New Planets, Harmonics and the science of Sound.
John in New York asked:
Is white noise something to do with gravity or the big bang?
If I play a nice pure tone, then that's got a particular frequency. But if I were to play all notes together, then that starts to become what you might call noise. Let's imagine that you played every single note that you can possibly imagine, which would not only be the white and black notes on the piano, but all the notes in between. In acoustics we would call that white noise. It's not just sound where you find vibration. You find vibration and waves in the surface of water, light is a wave, you'll find waves in slinky springs, and all over the place. You may have heard of things like the cosmic background radiation. Actually these are all electromagnetic waves of various kinds and light can be as much white noise as anything. So the reason it's called white noise is because we know that white light is made up of all the colours of the rainbow; lots of frequencies all at once. So white noise is taken from white light. When there was the big bang all sorts of frequencies were emitted. The noise from the big bang had one peak frequency so it's not all the frequencies at once and so it probably isn't really white noise.