Question: how is it possible that when you tune a radio or a tv and it has no signal the sound that it makes is what it would sound like whilst the big bang was happening? (putting there is no sound in space aside)

Ian Stephenson answered on 23 Jun 2014:

The noise that you hear is called white noise.

In the same way that white light is made up of all different frequencies of light (colours), white noise has all the different frequencies of sound mixed into it equally.

Sudden noises (like clapping your hands) happen to have exactly the same frequency, but in the case of an “impulse” (a loud bang), all of the are lined up to they push at the same time.

Imagine a crowd of people all pushing and pulling at different speeds – that’s white noise. They’d just jostle around and it would be pretty random. Now imagine that they all push and pull at different speeds, but they all start pushing at exactly the same time – there’d be a big collective push forwards, followed by effectively no movement as they call cancelled out.

This kind of randomness is in lots of things, but a small part of what you hear on an un-tuned radio is the different frequencies that are echo’s of the big bang.