[jyl]

I don't remember the physics, but doesn't the strength of a omnidirectional radio signal diminish with the square of the distance from its origin? Has to do with the formula for surface of a sphere? So if a radio signal is "X" strong 1 mile from the transmitter, it will be 6 trillion squared or 4 x 10^25 times weaker when it reaches Alpha Centuari? I don't really see how such a weak signal can be distinguished from background noise, including that produced by Alpha Centuari itself? I can see if the signal is a supernova, but some local FM station broadcasting "Dancing Queen"? Anyone who knows the math, please explain. Thanks.