First things first: I definitely believe that there is other intelligent life in the universe. The universe is just too damn big for it to be just us humans. I guess it's kinda funny, I have a lot of faith in this, probably the kind of faith that Christians are supposed to have in Jesus. But I'll probably die without ever knowing for sure.
This does not mean I believe in UFOs. I'll concede that it's possible that Earth has been visited by extraterrestrials sometime in the past 4+ billion years. I even have my private suspicions that life on Earth may have started from some extraterrestrial "seed" -- some kind of spores or chemical precursors that floated through the void for a long time until they came to the Earth and somehow flourished and after a million or billion years became a thriving concern. Where did that seed come from? Who knows -- in one or more places life arose "naturally" and -- as living things are prone to do -- spread itself everywhere it could. I could be wrong and life really did arise spontaneously on Earth. I'm not complaining.
But people bring up the Fermi Paradox -- if life exists elsewhere in the universe, how come we haven't met them yet? There are many possible reasons for this:
- We really are alone.
- Intelligent life exists but it's uncommon.
- There's a whole galactic Internet out there -- but it uses some kind of technology that we can't detect.
- Etc.
I have my own thoughts on this. Part of the Fermi Paradox is the assumption that any intelligent species will completely colonize the galaxy in just a few million years, because they'll inevitably colonize nearby systems, and those colonies will eventually send out colonies, etc. It's a big self-replicating system that grows and grows until life is everywhere.
This may not be an original thought --and I have no evidence to support this, it's simply an idea -- but what if we are one of those colonies? Referencing the aforementioned "spore" idea, maybe we're part of the outwardly spreading wave, not yet at the point of sending out our own 'child' colonies.
Which still doesn't answer the question "where is everybody?". Strictly speaking, it's "improbable" that we would be the most advanced technological race in the neighborhood. But somebody has to be first, and it's not impossible that it's us. Just unlikely.
One theory -- one that I find easy to believe even though it scares the hell out of me -- is that advanced civilizations tend to be really, really quiet. Not because their communications technology is uber-efficient (although that won't hurt), but because It's A Jungle Out There.
The Russian astronomer Nikolai Kardashev came up with Kardashev Scale, which is one way of thinking about the sophistication of hypothetical civilizations throughout the universe:
- A Type I civilization has achieved mastery of the resources of its home planet.
- A Type II civilization has achieved mastery of the resources of its primary star and associated planets.
- A Type III civilization has achieved mastery of the resources of its entire galaxy.
Neat, mind-expanding stuff, but one thing to take away from it is that civilizations use resources. Given that the universe contains a limited number of resources, some forward-thinking civilizations, recognizing that they are growing larger and larger, might decide that any competitors for resources are a Bad Thing.
I trust you can see where I'm going with this. The Great Big Silence In The Sky may be due to a combination of a) smart civilizations keeping themselves hidden and b) not-so-smart civilizations getting wiped out by other civilizations who want to eliminate the competition.
This is one reason why Alien Invasion movies drive me crazy. Sure, it's possible that the aliens want to "enslave" us for some unknowable reason. But I'll bet you a dollar that we don't have much to offer any civilization that's capable of interstellar travel -- except for our resources. Practically speaking, it'd be a lot easier to simply wipe us out and mine our system at leisure.
And believe me, we'd be easy to wipe out. I've been reading science fiction for over forty years and there's no shortage of ideas on how to kill off the human race, and that's just from writers trying to earn three cents per word. Imagine an advanced race who really put some serious thinking into the matter.
And forget Independence Day. Probably the simplest, cheapest, most pragmatic technique would involve dropping a big rock on us. Or a bunch of little rocks -- traveling at relativistic velocities. They wouldn't even need to leave their home system -- just put some kind of drive / navigation units on the rocks and point 'em at Sol and let 'em rip. When they get close enough they target Earth and *boom* it's Game Over for the human race.
I'm admittedly making a fair number of assumptions here: that interstellar travel is difficult and there's no way to travel faster than light, that advanced civilizations aren't necessarily peaceful and there's no magic way to create energy and matter (ie, resources) from nothing. I'd be happy to be proven wrong on any of these points.
Let's put all that aside for the moment, though, and assume that aliens don't want to kill us outright. Why won't they talk to us?
One thought I've had is that the aliens are out there -- and they don't want to talk to us. Either because we have nothing to offer them, or -- maybe -- because we scare the hell out of them.
Not that we're in any position to wage interstellar war at this point. But let's be honest: we are an aggressive, warring, intolerant species. Even our entertainment is full of violence, conflict, and an unspoken assumption that the human race is somehow superior. If we made radio contact with another race that was just like us, we'd be terrified.
A well-worn cliche in science fiction is that war-like races like us inevitably wipe ourselves out -- to the grateful relief of the peaceful races of the universe. What if that's true? Maybe they're out there just waiting for us to commit racial suicide.
One final thought on this topic: maybe it's quiet because everybody moved?
I'm serious. There's a passage from Carl Sagan's novel Contact that's always stuck with me.
"If we're figuring out ways to extend our lifespans, think of what those creatures on Vega must have done. They probably are immortal, or close enough. I'm a practical person, and I've thought a lot now about immortality. I've probably thought longer and more seriously about it than anybody else. And I can tell you one thing for sure about immortals: They're very careful. They don't leave things to chance. They've invested too much effort in becoming immortal. I don't know what they look like, I don't know what they want from you, but if you ever get to see them, this is the only piece of practical advice I have for you: Something you think is dead cinch safe, they'll consider an unacceptable risk."
One of the things that I think that most science fiction has gotten wrong, from square one, is the unspoken assumption that all life lives on planets. Planets are relatively unsafe places to live: you have to deal with earthquakes, volcanoes, asteroid impacts, and other things that make death easy and immortality difficult. I suspect that truly advanced civilizations -- who may indeed have achieved some form of immortality -- will live in nice, controlled, predictable, and secure space colonies. And these space colonies may not be located anywhere near a star. Stars are great energy sources but sometimes they act up and turn into supernovas and gamma ray bursters (from the Wikipedia article: "It has been hypothesized that a gamma-ray burst in the Milky Way could cause a mass extinction on Earth.") -- which can also be problematic for immortals.
So maybe they moved ... to some nice quiet safe place in the vast gulfs between galaxies. Which means they're very very far away, and also very hard to detect. What do they use for energy and other resources? I don't know -- maybe they took some black holes with them and use those for energy. Maybe they have a vast automated industrial pipeline, tens of thousands of light years long, that ferries in resources from neighboring galaxies. It's just a guess -- but if you're looking for total security, safety, and control over your environment -- it's hard to think of a better place to live than those dark, empty, and uneventful spaces that separate the galaxies.
