I don't get why people refer to the silence. Considering the only program we have at the moment, SETI, is far from conclusive, an the parameters required for it to succeed are so narrow that we could be smack dab in the middle of a galactic conversation between hundreds of sentient, intelligent species and never detect a single one. I find it far shortsighted to refer to the silence when our technology is in its infancy at detecting ET. If an ET civilization was living on a world orbitting Alpha Centuari AB, with our exact level of technology, they would be unable to detect us, unless we sent a signal there way, on a specific frequency, and they happened to be listening to our direction, at that frequency, at that moment, to hear it.
You are missing the point.
The Universe has been around long enough that other civilizations would exhibit a broad spectrum of technology with some being more advanced, others less advanced than us.
So why are the more advanced ones so introverted?
My feeling is that we are so far behind the evolutionary curve of advanced space faring races that we are not worth contacting. It is only our hubris that makes man think he is the end all product of evolution.
Could you imagine man trying to contact the dinosaurs on a planet a million years behind us in evolution?
Man is still evolving. We have artificial hips, ears, knees etc. Someday the entire body will be replaced (TP=Total prosthesis) and will man still be man?
AI could come to dominate. Perhaps man will rapidly become a foot note?
We look for the first cell. Perhaps space faring races see the invention of the transistor back in Bell labs as their equivalent of a 'first cell' progeny.
Pesse (We got a long way to go and a short time to get there.) Mist
Well soon it wont matter. As exoplanet research and detection gets better, we will eventually reach the point where we can detect the signatures of techology in an exo-atmosphere, and from that, infer that there is an intelligent civilization living on that world, (For example, if we detect CFCs in an alien atmosphere, since CFCs do not occur naturally, we know someone made them) so I think more likely we will find them before they ever reach out to us.