[cogitator]

Oh puh_leeez. If there were a hundred million in this gallexy and half of them were more advanced than us, we would have found some hint by now. Maybe there is something more unique about our little planet than what the experts assume.

I found the thread intriguing, and your comment was one of the most thought-provoking. Based on a quick search, we are about 28,000 light-years from the center of the Galaxy, so the Milky Way is approximately 60,000 light years wide. What if, 20,000 years ago, there was a civilized planet on the "opposite side" of the galaxy where the technological era lasted 5,000 years. (We don't know how long a fully-technological society will last.) Say that they were fully-technological exactly 20,000 years ago -- let's make wireless electronic communication (radio) the mark of a fully-technologized society. Imagine that within a century they start broadcasting a signal spaceward to alert any other possible technological societies that "We Are Here". Imagine that they broadcast this signal for the full duration of the existence of their society.

Under that scenario, the signal that they started to broadcast 20,000 years ago would still have 40,000 years to travel before we could detect it; and at that point that society would have passed from existence 55,000 years ago.

While I like the idea of SETI, I think that the distances involed make detection of anything highly, highly, highly unlikely, even if this single galaxy had hundreds of technological societies.

[Always Right]

The milky way I think is closer to 100,000 light years in diameter. If it were a ball, it would have a volume of roughly 1.5 x 10^15 cubic light years. Since it is more of a disk shape, the actual volume is probably closer to 5 x 10^14. There are really just too many unknowns to make a logical guess at how close the nearest live planet would be. To even make a ballpark guess you would need to know a bunch of things like the average time a planet became habitable, and how long it remained that way. The probability that intelligent life developed and became smart enough to survive even when the planet became inhabitable. The errors in the assumptions and the number of unknowns make any calculation nothing but a wild ass guess. But if we are not picking up any signals right now, the chances of picking a signal up any signal over the next five years are zilch. Even if it were possible there were a hundred million habitable planets in this galaxy, the number of planets that are habitable at any given time is much much much less than that.

[SunkenCiv]

:') The distance at which the strongest signal on Earth could be picked up by technology similar to ours used to be about 10 light years; now it is about 50, so regardless of the actual size of the galaxy, we won't be hearing from a society as distant as your example. Also, as we make no active effort to be heard, some nearby ET's picking up one of our signals is unlikely. Given that no one here has an interest in doing anything but listening, I don't see any reason to expect any other civilization wanting to try to broadcast an interstellar hello signal, even assuming they haven't discovered something more advanced than radio.