So this is a variant of this other question.
- I know stars are big, they radiate a lotta energy, they have spectral lines. But how dense are these spectral lines and is there a noise floor at frequencies other than the spectral lines where it would be most logical for intelligent beings to squeeze in an EM signal? Are these holes in the spectrum quiet enough? I just can't imagine some mortal species competing with a canopy of stars to get a message through unless there are some really quiet spectral holes.
- Suppose such holes exist (and I imagine astronomers know about them, it's just that I don't), given inverse-square attenuation, how far can we expect to hear a 100 Megawatt transmitter with a decent directional antenna that is pointed to where ET will expect our star (and planet) to be in the hundreds of years in their future? I am assuming that ET picks a star that they think might have a habitable exoplanet, they know the distance to that star, and project where in their space that star will be when their beacon would arrive at that star.
I mean, can we expect to hear anything from further than 100 lightyears? 1000 lightyears? Then, within that sphere, given the Drake equation and whatever are the going parameters for it, what would be the likelihood of a civilization to appear in that window of space and time? It seems to me to be low. (100 LY)³ isn't all that big of a chunk of our galaxy.
Essentially, my question is: Does SETI even have a fool's hope?