User blog comment:Pgrobban/Computers and random numbers/@comment-24956068-20160118202922/@comment-25968376-20160118203809

The way I understand is that you can have basically anything as atmospheric noise. It could be temperature, pressure, voltage in a current and so on. When you measure these with a sensitive enough instrument, you will see that there are huge variations (for example the temperature in a city within an hour can be any number between 12 and 13°). These variations are also deterministic, but in order to accurately predict these, you have to study the position and speed of every molecule in the universe, which is quite difficult...