This article in the New Scientist reminds me of that amazing intro to the movie Contact with Jodie foster, which follows the radio waves of terrestrial TV transmission out into space. The camera flies out from Earth with the audio of the television transmission in the background. The further the camera gets from Earth, the further back in time the transmissions get, until it gets far enough away that it catches up with the first TV broadcast that could have been heard from space. Ironically, it’s a speech by Hitler at the 1936 Olympics in Munich.
The irony now is that as technology advances we rely less and less on terrestrial broadcasts, and more and more on cable or satellite TV. Those transmissions that leak into space, the first thing an alien would probably “hear” from our planet, are drying up. Earth is going quiet.