Because we live in 3-D space, the intensity of any radiation decreases with the distance as 1/R^2 (inverse square). Suppose, that one out of a million stars in our galaxy has intelligent life around it (very optimistic estimate - then there are about a million civilizations in our galaxy alone). Because average distance between stars in our neigborhood is about 3-4 light years, then nearest intelligence beyond our Solar system is about 300-400 ly away.Using 10-terawatt transmitter (=10^13 watt, which is equivalent to the power produced and consumed by our entire civilization, and which is about million times more powerful than any transmitter we have so far)you can only deliver 10^-25 watt/square meter that far, or 1 quantum of radio waves per 10 second per square meter (on 21 cm H-line). This is basicly maximum amount of bits of information you can obtain from original message. Not much, not to say about various noise sources in receiver end and much more powerfull blending radiation from natural sources (stars, galaxies, etc.).Reflected radiation will be another similar factor wakier (which leaves no hope to detect it at all at such distances). Another problem is waiting 600-800 years for possible respond (and speed of radiowaves in vacuum = c, which is constant, and can not be accelerated by gravity or anyrthing else). So realisticly, there is not much hope in catching aliens' TV signal not to say about videoconferencing with them. Too far.
Alex.

• Re: Radio signal becomes too weak when it reaches other intelligence - bladesinger - January 18, 2001 - 04:12 UTC