Rob Dekker wrote:
"Russ Childers" wrote in message ...

snip

25LYs only encompasses a hundred stars or so, but the silence so far says something about
the prevalence of ETIs in the neighborhood. At least something about the prevalence of
ETIs that can and want to communicate with us.

Not necessarily. There could be an Alpha Centauri civilization
beaming radio in our direction at 6.022 GHz for the past 50 years.
If we don't look at Alpha Centauri in the 6.022 GHz band, then
we won't detect them.


Maybe ETI are doing powerful planetary
radar. Maybe they are communicating with a colony on a star
a couple of light years away. Maybe they are trying to
communicate with a space probe which has a damaged receiver.
If we happened to be in line with these powerful, beamed
broadcasts, we could conceivably receive a LOT of power.



True. But the further advanced a civilization, the narrower the beam to the probe will be,
so the chances of being in 'line' with that beam diminish.

Not necessarily. Suppose they are using radar to detect
"killer asteroids". A narrow beam would slow down their
search.

We can only guess at the power, frequency, modulation, and sky
coverage of ETI transmitters.


Russ