Even if alien life does exist, we'll probably never prove it definitively not only because we don't really even know what to look for, but even if we somehow managed to know we also have to remember the unfathomable size of the universe and it's incomprehensible size that I don't think any civilization, regardless of how advanced, could traverse. For God's sake it's been nearly 14 billion years and yet we've picked up absolutely no evidence of anything. We might as well be alone.