[Brett66]

So if the odds are only one-in-a-billion, that gives us about 400 civilizations in our galaxy. Most likely these 400 civilizations would be farther than 1000 light years away so we won't find them by SETI efforts. The only way is to build huge interferometers and scan millions of star systems. it will be dumb luck if we stumbled on another Earth. I think we need to focus our efforts to establishing bases and colonies on the moon, this is like trying to win the pick-six.

[RightWhale]

Consider also the lifetime of civilizations. The odds that there is another civilization living right now in our Milky Way is close to zero. Maybe some are living right now in other galaxies, but not every galaxy. We could never come across another civilization even if there are or have been or will be billions in the visible universe.