On Tuesday, January 2, 2018 at 12:54:07 AM UTC-7, Eric Flesch wrote:

On 01 Jan 2018, Gary Harnagel wrote:

G-type stars that are gone now
but the intelligent species "hatched" by them have migrated to a younger
star. At only 0.1% the speed of light, generation ships could cross the
entire galaxy in a mere 0.1 billion years.

But they never came here, to Earth.
And yet they would have spread
out over the galaxy, the same as yeast in a Petri dish. What part of
the Petri dish escapes the yeast? None. There is your evidence that
no such alien civilizations exist.

OTOH, brute-force interstellar travel (i.e., space ships) may be too
difficult for civilizations a few thousand years beyond ours, given
cosmic radiation and the possibility of collisions with Oort cloud
objects. Interstellar travel might have to wait hundreds of thousands
of years.

I try to imagine what a mature civilization 100,000 years ahead of ours
would have as goals. For one thing, they wouldn't be like Captain Kirk,
but they may have the Federations non-interference mandate. In any
case, they wouldn't be yeast. They would be:

There may be millions of inhabited worlds circling other suns, harboring
beings who to us would seem godlike, with civilizations and cultures
beyond our wildest dreams. --- Arthur C. Clarke