This essay by astrophysicist Adam Frank in the New York Times is upbeat, confident: "Yes, There Have Been Aliens." Basically, he argues that we've now observed enough Earth-like planets outside our solar system that unless the odds of life (and intelligent life, and intelligent life capable of radio communications, etc.) coming into being are much, much smaller than most scientists have believed, then alien civilizations that are at least something like our own have appeared before elsewhere in the galaxy.
But! Frank and his colleague Woodruff Sullivan get to this conclusion in a way that's pretty distressing. They relax any assumptions about how long such a civilization might last.
See, if you're trying to figure out the odds of contact between humans and aliens, you need to have some idea about how long alien civilizations stick around. If, in general, civilizations last a long time and keep moving up the Kardashev Scale, they're more likely to bump into each other. If, on the other hand, they usually wipe out their own species with nuclear weapons, global climate change, gamma rays, or (insert calamity here) shortly after getting a little light industry going, then they'll keep missing each other.
In his treatment of the Fermi Paradox, Tim Urban calls this "The Great Filter." We don't know if the Great Filter is ahead of us or behind us. If it's behind us, then complex/intelligent life is super rare -- much smaller than even Frank and Sullivan's consensus low estimates. If it's ahead of us, then we, or any other species lucky enough to make it this far, will most likely die off or (best case scenario) get stuck more or less where we are now.
In short, humanity may not be first, but it might very will be next.
First contact with an alien civilization will be a momentous event in the history of Earth. Unless the other civilization is kind of a dick. Tim Urban didn't quite cover this scenario in his post about the Fermi Paradox.
Edward Snowden has come up with a solution to the Fermi Paradox that I hadn't heard of before. Maybe we haven't discovered intelligent life elsewhere in the Universe, says Snowden, because their communications encryption is indistinguishable from cosmic background radiation.
"If you look at encrypted communication, if they are properly encrypted, there is no real way to tell that they are encrypted," Snowden said. "You can't distinguish a properly encrypted communication from random behaviour."
Therefore, Snowden continued, as human and alien societies get more sophisticated and move from "open communications" to encrypted communication, the signals being broadcast will quickly stop looking like recognisable signals.
"So if you have an an alien civilization trying to listen for other civilizations," he said, "or our civilization trying to listen for aliens, there's only one small period in the development of their society when all their communication will be sent via the most primitive and most unprotected means."
After that, Snowden said, alien messages would be so encrypted that it would render them unrecognisable, "indistinguishable to us from cosmic microwave background radiation". In that case, humanity would not even realise it had received such communications.
Snowden shared his hypothesis with Neil deGrasse Tyson on Tyson's podcast, StarTalk.
Great post on the Fermi Paradox, aka if there are so many potential intelligent civilizations out there in the universe (possibly 10 quadrillion of them), why haven't we heard from anyone?
Possibility 5) There's only one instance of higher-intelligent life -- a "superpredator" civilization (like humans are here on Earth) -- who is far more advanced than everyone else and keeps it that way by exterminating any intelligent civilization once they get past a certain level. This would suck. The way it might work is that it's an inefficient use of resources to exterminate all emerging intelligences, maybe because most die out on their own. But past a certain point, the super beings make their move -- because to them, an emerging intelligent species becomes like a virus as it starts to grow and spread. This theory suggests that whoever was the first in the galaxy to reach intelligence won, and now no one else has a chance. This would explain the lack of activity out there because it would keep the number of super-intelligent civilizations to just one.
Update: If you prefer to watch engaging videos instead of reading text, here's six minutes on the Fermi Paradox: