Fermi's Paradox

Enrico Fermi, one of the inventors of the atomic bomb, famously asked of intelligent life in other star systems, "where are they?" In the fullness of time, this led to the SETI project, which is using radio telescopes to search for signals. On a related note, several SETI theorists, including the late Carl Sagan, assumed that our own radio broadcasts might be picked up by an alien civilization.

Well, Jerry Pournelle links to this site which suggests a different possibility. We're not hearing the aliens and they're not hearing us because of attenuation.

According to the article, even the best current radio telescope in existence, the 305 meter set at Arecibo, couldn't detect standard-strength broadcast signals (in the AM band) from Mars! FM fades by Saturn, and that's pretty much all she wrote. To pick up a 5 megawatt UHF broadcast signal from Alpha Centauri we'd need an antenna with a 33,000 kilometer(!) diameter - bigger then Earth.

Now, I'm not a radio expert (paging jeff_duntemann), but the article suggests that unless the aliens are trying to contact us by sending a focused signal, we're not going to hear them. Considering the number of stars just in our galaxy, one literally has a better chance of winning the lottery then getting a signal.

Parenthetically, some of the science fiction thinkers suggest that war in deep space is impossible, or at least very difficult, because of passive detection. ETA: see this site. Simply put, the heat from a space ship would be seen and trackable anywhere in the solar system. Since the heat energy would follow the same attenuation principles as radio waves, I suggest that this article puts "paid" on that concept. ETA: Or does it? I don't think I understand wave physics well enough to tell.