There is another premise that is faulty: that the answer to "where's everybody" is that "since we see nobody, there is nobody". But for all we know the planets around Alpha Centauri may be teaming with life, and there would be no way for us to detect that. If only 1% of the solar systems in our galaxy host intelligent life, then the number of intelligent life forms would be truly mind-boggling, yet we wouldn't be able to detect a whisper of their presence. For the simple reason that space is also mind-blowingly vast, and all signals decay with the square root of the distance.