Taking a simplistic view on the detectability of highly advanced civilizations is a bit naive.
Judging by the only example we have (the Earth), life depends upon a variety and quantity of elements that require much time to accumulate through the stellar birth/death cycle, technologically advanced life even more so. That is to say, you aren't likely to find ten billion year old technologically advanced civilizations - stars that old don't tend to have enough heavy elements in their systems.
There's also a problem with windows of detectability - you're only going to be able to detect civilizations who are temporally and spatially situated such that they are even possible for us to detect. They would need to be extant and detectable in the right place, and at the right time. For example, a civilization that is 1B light years away isn't going to be detectable if it went extinct 900M years ago. Nor would a civilization that achieved a threshold of detectability 900M years ago be detectable if it's 1B light years distant.
Judging by the only example we have (the Earth), life depends upon a variety and quantity of elements that require much time to accumulate through the stellar birth/death cycle, technologically advanced life even more so. That is to say, you aren't likely to find ten billion year old technologically advanced civilizations - stars that old don't tend to have enough heavy elements in their systems.
There's also a problem with windows of detectability - you're only going to be able to detect civilizations who are temporally and spatially situated such that they are even possible for us to detect. They would need to be extant and detectable in the right place, and at the right time. For example, a civilization that is 1B light years away isn't going to be detectable if it went extinct 900M years ago. Nor would a civilization that achieved a threshold of detectability 900M years ago be detectable if it's 1B light years distant.
