As far as I know, it was the great physicist Enrico Fermi who first asked that ugliest of all ugly questions: "If there is intelligent life elsewhere in the universe, where is everybody?"
Fermi was looking at the youth of our species in geological terms. In the lifetime of a solar system or especially a galaxy, 10,000 years is nothing. If after only 10,000 years we can conceive of the idea of interstellar travel and have discovered enough of physics to know (roughly) how to approach it, why isn't the place already crawling with aliens? Thousands or (more likely) millions of other species on other worlds must have gotten this far and much farther long before Earth ever condensed from interstellar matter. We already know that other planets exist because our telescopes are now good enough to see them! So why do we aim our most sensitive antennas at the stars and hear...nothing? Where the hell is all the action?
A great deal of good SF has been devoted to presenting possible answers to this question. What I want to do in this short essay is gather as many of the answers to the Fermi question as I can, and put them down in coherent form, with my own views on the matter. If you read this essay and can elucidate one or a few that I haven't though of, send me some e-mail and I'll roll your answers in with my own, along with any pertinent commentary you might have.
(I believe it was physicist Frank Tipler who suggested that even if they didn't come themselves, more advanced civilizations would certainly send self-replicating robots to every planet in the galaxy. I contend that this is unlikely, because it amounts to infecting the galaxy with a monstrous mechanical virus--something no ethical race would ever choose to do. Absence of robots is by no means evidence of absence.)
So. Let's begin. Hey, out there! Where is everybody!?!?!
Answer #1. They're Already Here.
I hate this one. Many would hold that UFOs are alien spacecraft, that they're here and have been here for a long time. We don't perceive them because we simply refuse to believe in them. Well, I'm sorry--we don't perceive them because if they exist they hide pretty damned well. I've been an amateur astronomer for over thirty years. I've never seen anything in the skies that comes anywhere close to being "unidentified." Nor has anyone I've known well enough to trust. Also, where were they before 1947? (I know, I know, they "heard" the neutrinos from our first nuclear reactions and came a-runnin'. I don't buy it.)
There is one worm in my discontent with the whole UFO business: The CIA seems awfully interested in them--way too interested for comfort. The CIA doesn't investigate sightings of elves, nor Near-Death Experiences, nor any number of other stock-label twentieth-century weirdnesses. But their tracks all over the UFO public record, striving mightily to debunk the whole UFO movement and convince people that UFOs do not exist. This bothers me, because those guys aren't stupid--and debunking the paranormal isn't anything close to being part of their job. The fact that they spend a great deal of (my) money trying to convince people that UFOs don't exist makes me wonder what's really going on. The Company Doth Protest Too Much, Methinks.
If there's any truth to all this Roswell nuttiness, sooner or later the truth will out. You can't hide something that potent forever.
Answer #2. We're All There Is.
It may be that we are the only intelligent species in the universe. This is outrageously unlikely, from a statistical standpoint. One cool thing about our universe is that a glass of water over here is the same as a glass of water somewhere out in a planet in the farthest galaxy you can see. Stuff that exists somewhere will exist elsewhere; in fact, stuff that exists anywhere can probably be found...everywhere.
On the other hand, vanishingly unlikely isn't the same thing as impossible. And people who scoff forget that when we are the Fabulously Unlikely Accident, our unlikeliness factors out and goes away--otherwise, who'd be asking the question?
There are levels to this answer. It may be that life itself is unlikely--as Norman Spirad postulated in his excellent Riding the Torch. What we see of life's basic mechanisms, however, implies that if the right stuff is in the primordial soup, the meatballs will soon begin to dance of their own accord. Chemistry seems to point toward life in ways we are only beginning to grasp.
Most people who hold this view claim that intelligence is the toughie. (Vernor Vinge made this point in Marooned in Realtime.) Something truly remarkable happened fifty or a hundred thousand years ago that never happened before and will never happen again. Because we don't know how intelligence happens, it's tough to say how unlikely it truly is.
This view appeals to theists, because it implies that intelligence was a special, deliberate intervention of the Divine in what would otherwise have remained a worldwide zoo of happy animals. The bonus, of course, is that there could now be trillions of habitable planets out there with no one on them, waiting for us to be fruitful and multiply--if only we could figure out how to get there.
My view is that there are only two possibilities in this statistics game: We are either alone, or the universe is crawling with intelligent life. There can be unlikely accidents in the universe, but anything that can happen more than once will likely happen every time the right ingredients are in the right sort of pot. So if we are not in fact alone, the club has a lot of members--but Fermi's question remains.
Answer #3. Everybody Blows Up Before They Grows Up.
The Cynic's Special in this supermarket of ideas has long been that nobody's come to visit because the life span of an intelligent species is only until they discover nuclear weapons, or biological weapons, or in some other way do themselves in as mere infants on the cosmic time scale. They haven't come to visit because they don't last long enough to invent starships. We don't hear their TV sitcoms because their radio bubbles are very thin--a hundred light years, perhaps--so blink and you miss it. We've only had radios of consequence for about seventy years, so it's very unlikely that we've been listening just as that thin wall of radio chatter passes by and vanishes. If we listen for another thousand years we might catch a couple--but that doesn't help us in the here and now.
Years ago this was my view--but then the Berlin Wall fell, the Russians got at least modestly civilized, and everywhere I look a certain welcome sanity seems to be breaking out. Sure, our inner cities are a mess, but our international situation has never been better in all human history. (I'm not a very good cynic, sigh.) I may still be wrong, but I keep thinking that we ducked the bullet, and if we can do it the other guys can too.
Besides, if even one race survives to build starships, in a few million years they should be everywhere. Which leads us to...
Answer #4. We're Still In A Protected Wilderness Area.
The gist here is that the Galactic Council has thoroughly walled off our solar system from the hoi-polloi to give us a chance to grow up. Visits from the starfolk are strictly forbidden--except when an occasional saucer full of evil Greys sneaks past the fences to cut the ears off our cows and abduct a New Ager or two.
I guess this is possible--especially if starships don't radiate much. If star travel is a really energetic phenomenon, we'd probably have detected it by now. On the other hand, if there is some sort of "transfer point" or stargate through which all traffic into our system must pass, it would be easy enough to post a guard, leaving nothing but the "hard way"--sublight travel--to reach our Earth. (This was the Moties' dilemma in the Niven/Pournelle adventure Mote in God's Eye and its sequel The Gripping Hand.)
There remains the question of why we haven't heard all their radio traffic from the multitude of home planets lying in every direction. The simple answer: They don't use it. Radio as we know it is simply impossible for interstellar distances. Within a solar system it gets mighty inconvenient as soon as you start crossing planetary distances. Right on the home planet, well, broadcast radio and TV are fearsome energy-wasters. I would expect that communication on and around a highly advanced civilization would be through cables and very tight microwave beams. That's the way we're going--high-power broadcast wireless media will probably be extinct in another thirty or fifty years max--and we're cosmic infants.
The "radio bubble" due to broadcast communications radiating away from every inhabited planet is very thin: Probably only the 100 light years it takes for technological history to progress from primitive radio to high-bandwidth global network. We've really only been listening for such things for thirty-odd years, so the chances of missing all of them so far are pretty good. If we listen closely for another 100-200 years I think the chances of picking up someone's bubble will approach unity. Again, that doesn't help us at the moment.
This answer appeals to me, because it implies the order of a galactic civilization with some sort of ethical sense. One has to wonder, however, when they'll judge us fit to "graduate"--or whether we're not so much in a game preserve as under quarantine.
Answer #5. Everybody Gets Absorbed Into The Overmind Before They Visit.
Arthur C. Clarke nailed me to my chair as a teenager with Childhood's End, the story of Earth's passage from a civilization of individual biological organisms to union with some sort of immaterial cosmic "overmind," the nature of which is not deeply discussed. The gist of it was that nearly all intelligent races have only a few thousand years as biological individuals before they naturally "graduate" to a nonphysical existence where the limitations of time and space simply don't matter. Starships are discouraged, because star travel somehow seems to inhibit the transition from "childhood" to the Galactic Overmind.
This is a weird one, but the more I learn about the weird nature of the human mind (and the possibility of psi being a reality) the less I'm inclined to write it off completely. I've been convinced that psi exists (see Margins of Reality by Jahn and Dunne for the research that convinced me--this is not nutcase stuff!) but I have no idea what psi's implications are. We'll have to shove aside vicious debunkers like the fake "scientists" of SCICOP before the concept will get a fair hearing and enough solid research to show us what's real and what isn't.
This, of course, is an answer that goes completely beyond physics. Is it possible? Of course. Can it be proven? I don't know. Apart from the ongoing radio bubble problem (which cannot be solved except by another few centuries of listening) it certainly explains why nobody's come visiting. And there's this funny notion I have that given a choice between living in a body trapped in spacetime with an absurdly low speed limit and living in some nonphysical realm where I can go anywhere in an instant and not have to spend most of my existence asleep, well, you know which way it would go. Biology is immobility.
Answer #6. The Fun Is All In The Fourth Dimension.
This one is my twist on #5 that doesn't jolt the materialistic view quite as hard. Basically, there may be some technology yet to be developed that yields more interesting things to do than poke around a mostly empty universe looking for planets full of other people to talk to. Maybe our own universe is a dud, and (to use e.e.cummings' words) there's another great universe next door, let's go!
Why would our universe be a dud? Well, maybe C is unusually low in our universe. Maybe in another universe the speed of light is measured in trillions or heptillions of miles per second, and star travel is just a matter of accelerating like hell for a few months to get to the nearest stars and back.
Or maybe breaking into hyperspace to avoid C-limits opens marvels loads more attractive than simple exploration of a plain three-dimensional space like ours. Maybe once you enter hyperspace you can't easily get back in--but it's so neat there that nobody bothers.
Basically, star travel is probably a horrible energy-sink, difficult to do, and maybe boring. If Something Else turns up that satisfied the need of an advanced civilization to dream and reach beyond itself, star travel may come off looking shabby and more trouble than it's worth. And no, I have no crisp idea what that Something Else might be.
Pure speculation on my part, obviously. But it's possible. So let it stand.
Answer #7. We're Psi-Challenged From Birth.
Maybe we're cripples and nobody wants anything to do with us. Maybe we're cripples and therefore nobody knows we're even here. Suppose that some small percentage of intelligent races--say one or two in a thousand--evolve without PK (psychokinesis--the "jaunte" of Bester's The Stars My Destination) and telepathy. Everybody else can communicate mind-to-mind (making radio irrelevant; perhaps no more than a laboratory curiosity or simply a medium for telemetry) and simply pop around the galaxy by thinking themselves from one place to another.
They identify other intelligent races by "hearing" their collective telepathic wavefront from a long way off, and just "pop" over for a visit under their own power. It could be that we lack this telepathic presence and therefore don't call attention to ourselves. It could be that a visitor or two has arrived on our world over the centuries, observed what to them would be the horrible lonliness of being trapped in our own skulls all our lives, and then run screaming back wherever they came from. It could be that interstellar jauntes require a telepathic "beacon" on the other side to home in on--something we lack that a properly endowed race would have.
This is an attractive answer because it explains everything: the lack of visitors and the lack of radio bubbles. There is some modest evidence for psi beginning to appear, so don't write this off as completely bonkers. If psi powers become commonplace in our future (as some insist they will) it'll be interesting to see who--or what--comes knocking.
Answer #8. The Bus Doesn't Stop Here.
Jerry Pournelle and a fair number of other SF authors have made hay with the notion that there is some sort of "transfer point" in every star system, through which all hyperspace-jumping interstellar travel must pass. Where the transfer point lies may be a complex function of a solar system's geometry--or just random chance. Now, suppose that our transfer point is somehow inaccessible, perhaps inside the Sun. Assuming that this is a truly fluky situation--say, one in ten thousand--there would be an abundance of interesting places to visit and one planet with broken machinery would not be missed.
This leaves the radio bubble issue, but if we're truly an ordinary world among millions and millions of other ordinary worlds, there wouldn't be a lot of reason for interstellar travellers to find other ways to visit us. "Scratch that one; let's head for Tau Ceti. It's right around the corner."
Answer #9. Bruno's Coming To Break Our Kneecaps
There's only one really scary answer in the collection: That there really are Berserkers (as in Fred Saberhagen's long-running series of the same name) and sooner or later one will come to visit. A Berserker is a Great Big Thing That Eats Planets. Trekkers will remember The Doomsday Machine (by far the best Star Trek episode ever) and Philip Jose Farmer fans may recall the horned abomination in The Unreasoning Mask that destroyed civilized races by dumping endless gigatons of steel ball bearings on them. (This sounds silly on the surface of it but Farmer makes a chillingly good case.)
The gist is that somewhere out there a really nasty mechanism is listening for us, and when our radio bubble crosses its kilometer-long antenna banks, it will turn around and start accelerating in our direction. What its mode of destruction is doesn't matter that much-- there are a surprising number of things that could wipe us out. The asteroid Eros, for example: Bruno would only need to give it a little noodge in just the right direction...
The weapon could be Bruno himself. If he's big enough, it doesn't matter much what he's made of: Just accelerating to half the speed of light and impacting on Earth would cause such havoc that life might never fully recover.
The Berserker machines could be self-replicating (they'd almost have to be, in fact) and there may be a Galactic Exterminator force of intelligent races who somehow ducked the Bruno Bullet and now hunt them down one by one. Doesn't matter; if even a few much creatures got loose, they could reduce the number of races that made it to starfaring age by 99%. We could wait a long time for radio bubbles from the survivors. But maybe we see the supernovae that the Berserkers detonate.
To avoid depression I choose not to believe this one. A machine of such power would have to be mighty big, and probably mighty slow. Or one would surmise. I hope.
Besides, there's one last answer, and it's a much better-if stranger-one.
Answer #10. Now That I Can Have It I Don't Want It.
Maybe interstellar travel is a kid's dream. By that I mean maybe it's a phase we're passing through on our way to true maturity hundreds or thousands of years from now. Maybe by the time we'll know enough physics and control enough energy to go to the stars...we just won't want to anymore.
I know this seems unlikely to most of you who are bothering to read this. Me, I remember a lot of the things I ached to have as a teenager that I have no taste for anymore, even though I could easily afford many of them now. I wanted a bright purple car. I wanted my own airplane. I wanted rare stamps. I wanted gold coins. I wanted to have sex with teenage girls, sheesh. None of that stuff does anything for me anymore, now that I'm an old guy of 44.
It's a slippery thing to define, but there is some sort of human mythic consciousness, and it changes over time. We "imagine" our place in the universe much differently now than we did when we were ancient Greeks. The stars then were the souls of the departed. Today, the stars are an affront to our pride: We can see them but we can't touch them. And it drives us batshit. Who knows what we'll see in the stars in another five hundred or a thousand years? Maybe the eyes of humanity will become bored with the physical world and turn inward. Maybe intelligence itself is a passing phase, or at least intelligence as we now define it. We must not fall into the trap of thinking that humanity has frozen solid and will never change in the future. It might be good, it might be bad--but we won't be the same a thousand years from now.
So...What Do You Think?
That's every answer I might hand to the poor departed Dr. Fermi; at least every one I could think of, put down in no particular order. Got any others? Let me know.
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