I'm always amazed by people thinking it is possible for distant civilizations to pick up random radio signals (typically television broadcasts) that were transm

I'm always amazed by people thinking it is possible for distant civilizations to pick up random radio signals (typically television broadcasts) that were transmitted on earth. Any signals spreading out in space already has to deal with an inverse square law due to the wavefront being spread out. However, the amount of noise stays roughly the same all over the universe (as near as we can tell). This means that "pretty soon" (depending on the original broadcast power) the signal will be orders of magnitude weaker the the noise level in any receiver. There are some techniques to pull up a signal from under the noise floor, eg using matched filters and the like. This is how GPS works. However, can only be done if you already know the signal that you are looking for. For GPS, this is not really a problem since it is well known what signal any given satellite will transmit at any given time. However, with TV shows (or any similarly information dense signal), the signal content is by definition not known already to another civilization. This is not even going into the fact that high-information signals can be pretty indistinguishable from noise anyway if you don't know the exact modulation type and parameters used. Pretty much the only way aliens will be able to enjoy our television broadcasts is if they come close enough to visit the solar system anyway, and by then they might as well land and look at cable TV... (For more information, take a look at http://www.bidstrup.com/seti.htm http://www.bidstrup.com/seti.htm or similar)