How far and wide have we looked? Have we seen evidence of extraterrestrial intelligence anywhere, yet?

The practical limit at which we could detect another civilization depends upon how advanced the civilization is. It’s been argued that a red giant star looks an awful lot like a Dyson sphere – think of a hollow ping pong ball the size of the Earth’s orbit, occupied by lots of ETs using essentially all their sun’s energy (the red we see is their waste heat). We’ve been listening for radio signals for a few decades, but we’re only capable ourselves of sending signals a light-year or so – and the nearest star is about 4 light-years away. (It’s cheaper to listen, so we listen – but anyone we hear will have mastery of much more energy than we have, and will have to be motivated to expend a lot if it to say “hello.”)

So it’s fair to guess that there aren’t any real advanced civilizations within a dozen light-years or so, and I personally can’t imagine that we’re alone in the galaxy, but the distances we’re talking about are truly immense, and the time it will take to have a conversation will likely be measured in centuries.

Unless we discover something unexpected…