I'm on a roll, LOL. Can't help it I've just become fascinated with this. This is the last link though
This guy talks more about the "filters" that could make spacefaring civilizations rare. But even if the things he mentions are true filters/rare events, still just like Jreed said above you have billions and billions of chances, so it would happen many times. So maybe there are other filters later on. Otherwise we should be seeing definite evidence of high level civilization/high energy production
SOMEWHERE in 100,000 galaxies. I've always taken a cautious view on it but even I think that is just a crazy absence. There's not even
One? In that huge sample size of
galaxies? Maybe per something about the physics or technology, it's just not possible to generate large amounts of energy artificially. Maybe it can only happen in stars......maybe nobody becomes a spacefaring species.
http://waitbutwhy.com/2014/05/fermi-paradox.html
One possibility: The Great Filter could be at the very beginning—it might be incredibly unusual for life to begin at all. This is a candidate because it took about a billion years of Earth’s existence to finally happen, and because we have tried extensively to replicate that event in labs and have never been able to do it. If this is indeed The Great Filter, it could mean that not only is there no intelligent life out there, there may be no other life at all.
Another possibility: The Great Filter could be the jump from the simple prokaryote cell to the complex eukaryote cell. After prokaryotes came into being, they remained that way for almost two billion years before making the evolutionary jump to being complex and having a nucleus. If this is The Great Filter, it would mean the universe is teeming with simple prokaryote cells and almost nothing beyond that.
There are a number of other possibilities—some even think the most recent leap we’ve made to our current intelligence is a Great Filter candidate. While the leap from moderate-intelligence (chimps) to human intelligence doesn’t at first seem like a miraculous step, Steven Pinker
rejects the idea of an inevitable “climb upward” of evolution: “Since evolution does not strive for a goal but just happens, it uses the adaptation most useful for a given ecological niche, and the fact that, on Earth, this led to technological intelligence only once so far may suggest that this outcome of natural selection is rare and hence by no means a certain development of the evolution of a tree of life.”