If an alien located on a planet 100 light years from here was to switch on a big, multi-frequency radio receiver, and record all the noises coming from outer space for the
hundred years, on all frequencies, how many soap operas, advertisements and new broadcasts would they pick up from Earth? Would a mass-market radio, similar to our Earthly equivalents, pick up anything? Over time, as the number of Earth transmissions increases exponentially, would the alien pick up a cacophony or a damp fizzle?
We've all heard the cliché that since the first radio broadcast, the Earth has been spewing all our bad soap operas, CB-radio call outs, airplane distress calls and re-runs of Boy Meets World
into outer space. This front of radio waviness is now as many light-years from Earth, in all directions, as the number of years since it was first transmitted (or so the cliché goes).
Now, it's also a function of radio wave propogation, that the Earth's ionosphere
is used to bounce some of those waves around the world. Thus people in Zimbabwe can pick up BBC World Service. So, presumably, not everything
ever transmitted will have left this planet, bound for space?
So, my question is about the percentage of those waves actually are travelling out in space? As time goes on, would the increase in transmissions from Earth's past begin to overwhelm all
alien radio equipment? In 100 light years of space, how much of the transmission would be dampened by gas, gravity, etc? As the 21st century portion of the wave arrived at the receiver, how long would it be before all
the transmissions sounded like 0s and 1s (announcing Earth's digital era)? Would the alien need special equipment? Or would any old radio pick up something, whatever frequency it was tuned to?
If two planets coincidentally started broadcasting around the same time, would the alien pick up a mixture of the two planets' frequencies? Or would the waves somehow cancel each other out as they meet on their individual journeys through space-time?