Where Is Everybody?A long-standing paradox in astronomy is sometimes called the Fermi Paradox after the famous physicist Enrico Fermi, who is the first person known to have posed it. If extraterrestrial civilizations exist, where are they? Anything that grows exponentially quickly gets very large, very fast. Something that doubles ten times is a thousand times as large. Actually 1024 times. The fortunate accident that a thousand is a round number in decimal, which humans use, and very close in binary, which computers use, is why we speak in terms of mega-, giga- and terabytes. (Nothing comes in kilobytes any more except tweets.)
So twenty doublings gets you to a million, thirty gets you to a billion, and nine more gets you to half a trillion. There are about 400 billion stars in our galaxy. So it would only take 39 doublings of a star-faring civilization to colonize every star in our galaxy. If it takes ten thousand years for a colony to take root and develop its own interstellar capability, that would be 390,000 years. That's an eye-blink in cosmic terms. So why isn't there massive evidence for interstellar societies? Or if they existed in the past and went extinct, why don't we see evidence of them? Why isn't there a global layer of extraterrestrial residue in the Ordovician or Jurassic?
Maybe we're first, or all alone (the same thing). That seems hard to believe given the rapidly mounting evidence that all (or nearly all) stars have planets. It also seems like special pleading. Scientists really don't like assuming we occupy a privileged place - it's proven false so many times in the past. Others object that we shouldn't try to read human psychology into aliens. Maybe they don't expand exponentially, or have a drive to explore. That's special pleading in reverse. It amounts to assuming we're uniquely aggressive or inquisitive, or so unusual that other races that develop science won't think anything like us.
Maybe there's some obstacle. Maybe civilizations don't stay viable for very long, or there's a technical obstacle too great to overcome. Or maybe they're out there, but keeping a low profile. Maybe they avoid pre-interstellar races, or maybe we're of no interest to them. We can barely read humans, much less try to head-shrink extraterrestrials.
Is it possible that there could be extraterrestrials that have the desire and means to colonize other stars, yet are free of the potentially fatal flaws we see in ourselves? There's one supremely important consideration. We don't see evidence of a widespread galactic civilization. That's serious evidence that such a combination of traits may not exist.
Oh, wait, "absence of evidence is not evidence of absence." Well, yes it is. If a hypothesis predicts large and easily observable effects, and we don't see the effects, that's evidence the hypothesis is wrong. I can't argue that, because there are no arrowheads in my flower bed, that Indians never walked across my (to them) future lawn. The probability of finding an arrowhead anywhere is low. But if you say that Indians a few thousand years ago had technology comparable to ours, that hypothesis predicts we should find ubiquitous advanced artifacts. We don't. Therefore the hypothesis is wrong.
But since we're the only intelligent species we know, it makes sense to start here. To begin with, we're really not all that inquisitive. The fact that we remained hunters and gatherers for a quarter of a million years doesn't inspire optimism. During recorded history, how many societies engaged in active, serious exploration? Renaissance Europeans, the Ming Chinese (but only for a short time), Polynesians, the Vikings. Maybe the Mongols and the Arabs, or at least individual adventurers. And that's it. The Romans, a society whose survival depended critically on knowledge of the world outside their borders, had almost no interest in geography. They never explored Ireland, or the Baltic. Black Africans never discovered Madagascar. The languages of Madagascar are Malayo-Polynesian, a fact that has been called "the single most surprising fact of human geography." Even today, with the world of knowledge at their fingertips, most people use the Internet for social messaging, games, and other less savory interests.
Space TravelIt's so much fun to watch science fiction from the early 1950's. The space program consisted of a wise old fatherly senior scientist, a young virile junior scientist, the senior scientist's beautiful daughter (can you see where this is going?) and a gangly kid from Texas or Brooklyn to provide assistance or comic relief or pathos (or all three). They worked in a basement lab at a university, or a back hangar at an Air Force base, and that's it. The sum total of the U.S. space program. Nobody pictured it would take the resources of a superpower to get into space, or that the impetus would be superpower rivalry. But we did, to the background beat of people complaining about "spending all that money on problems here on earth." But we persisted thanks to the virtues of being a republic, where decisions are (ideally) made by people smarter than the voters who elect them. And now that the technology has matured, minor powers like North Korea, and private companies, can orbit satellites. Barring catastrophe, that technology is here to stay. But resources were never an issue. Propellant is cheap. It was learning how to do it that was the problem. The vast majority of the cost of a satellite is skilled labor.
The next step is going to the moon. There are two important questions here. First, would civilizations on a world lacking natural satellites ever travel deep into space? Or would that first step be such a huge one that they decided it was impractical, impossible, or not worth it? More fundamentally, can civilization itself exist on a world lacking a large natural moon? Our moon stabilizes the earth's axial tilt within moderate limits because its gravitational effects overwhelm everything else. Mars, with only two tiny satellites, is much more affected by Jupiter, Earth, and Venus, and undergoes much larger changes in its axial tilt. It may be that the lack of large natural satellites is the real cosmic filter, that planets without large satellites undergo such huge environmental oscillations that life doesn't advance beyond primitive levels.
And once we got the the Moon, the geopolitical justification was gone. The people who wanted to "spend all that money on problems here on earth" got their way. Anyone else remember the Seventies? How we took all that Apollo money and eliminated poverty? Tore down the slums? Crime dropped to near zero? Me neither. Anybody care to tell me what we did get for it?
After the Moon, the next step is to Mars or Venus. Both would require a ship that can protect its passengers for many months, a lander that can get passengers to the surface and back, and a surface habitat that would provide protection for months while the party explores and waits for the planets to reach the right configuration for the return trip. We can do that for Mars, at least in theory. Venus is too hostile to venture to the surface now. But going to Mars will be a huge venture. We can do the logistics, provided we have the will as a society, and it will take years. We simply don't have the will as a society. The money needed to go to Mars will be an irresistible target for people who want to divert it to other purposes, or simply pocket it. More likely, incremental improvements in space technology will close much of the gap, just as private entrepreneurs are talking about returning to the Moon. The old conspiracy talk about all the blueprints for Apollo being gone is bunk. The blueprints don't exist on paper, but they do on microfilm. There are Saturn V rockets at Cape Canaveral and Huntsville. And we wouldn't recreate Apollo technology to go to the moon today any more than we'd run the Indy 500 in a Stutz Bearcat. Not when a cell phone has more computing power than Mission Control in 1969. (That said, do go to Cape Canaveral and take in the Apollo 8 launch re-enactment. Pay for the full price experience. It is money well spent.)
Much of the lure of venturing beyond the Moon is due to Mars being at least slightly earth-like. It has an atmosphere and evidence of a watery past. And there's that legacy of canals and imaginary Martians, H.G. Wells and Edgar Rice Burroughs. If there were nothing between us and Jupiter, or Mars were an airless planet like Mercury, or a lethal place like Venus, would we go? So maybe civilizations need the right planets nearby to have a motivation for long distance space travel.
So imagine we can eventually travel at will between the planets. Now for the stars. Now if we postulate things like artificial gravity or faster than light travel, all bets are off. On the other hand, if you can travel faster than light, the Fermi Paradox becomes even more acute, because it becomes so much easier to colonize the galaxy. So let's go to Alpha Centauri, 4.3 light years away. We need something that can keep a large crew alive - and sane - for many years. It will have to have room, the ability to grow food, its own space program (to land and come back), and the ability to fabricate everything it needs. I can't see anything smaller than an aircraft carrier, and that's being absurdly conservative. So let's say it weighs 100,000 metric tons (100 million kg) and gets to 1% of the speed of light. That's small enough that we don't have to worry about relativity. Energy = 1/2mv2 = 1/2 x 100 million kg x (3,000,000 m/sec)2 = 4.5 x 1020 joules. That's U.S. energy use for 50 years. That's not counting the internal energy needs to keep the ship lit and heated, keep plants growing, and so on. Then you have to spend an equal amount of energy braking once you get there. Unless you want to doom the crew to fly on forever. At 1% of the speed of light, the trip will last 430 years, or the time since Queen Elizabeth. The First. Can people keep a sense of mission and purpose for that long? Maybe they'll decide they prefer the ship instead. Or maybe they'll regress to pre-scientific levels and believe the ship is all there is. Although that theme has been used in a number of novels (and the ill-fated 1973 TV series, "The Starlost"), it seems far more likely that outcome would eventually - most likely very quickly - lead to a catastrophic breakdown of life support. If you up the speed to 10% of the speed of light, the round trip will take 86 years, maybe enough for someone who leaves as a child to come back. But multiply the energy needs by a hundred - velocity squared, remember? And then double it again, because now you have to accelerate back to Earth, and slow down once you get here.
There may be a relatively small historic window for us on Earth to travel into deep space. We saw one window open and close with the Apollo Program. There may or may not be another one. But why go to the Moon? Apart from scientific needs like building an observatory on the far side free from Earth's radio emissions, most of the things we can picture doing can be done better on earth. Mining? Well, almost all mineral deposits on Earth required water for their formation. The geology isn't the same. Mining metal rich asteroids may be more practical, and a lot of that can be done robotically. Then you do have the problem of getting thousands of tons of metal back to earth. Think of Chelyabinsk, multiplied by thousands. Drop it in the oceans? Tsunamis. Not to mention huge amounts of vaporized metal in the atmosphere during re-entry. Maybe we could fabricate the metal in space into aerodynamic landing bodies. On the other hand, using the metal in space to build spacecraft and space stations would be eminently practical. Why go to Mars? There may be some usable minerals in those deposits from Mars' early oceans. But there's the energy cost of getting it off Mars and getting it back to earth.
Libertarian colonies? Any libertarians who join lunar or Martian or asteroidal colonies will soon find themselves yearning for those regulation-free days back on Earth. Life in a colony where you can't survive five minutes unprotected outdoors will be regimented beyond belief. You don't waste anything. You don't pollute in the slightest. You will have to get permission for anything out of the ordinary. And you will work. I'm not even going to address Venus, where your habitat has to protect against 400 C temperatures and 90 atmospheres of pressure. We don't even have sub-sea habitats that can handle those pressures.
The only imaginable reasons to go to the moon or Mars for the foreseeable future are scientific, intellectual, and adventure. Any economic payback will be very far down the road. And human history doesn't offer a lot of hope that societies will engage in purely intellectual exploration for very long. To have regular travel to the moon or Mars will require travel simple and cheap enough for individuals and small groups to do it on their own. It's far from clear the economies of scale will ever permit that. Even taking a balloon to 25 miles and parachuting out required some pretty massive financial support.
If we can find habitable planets the equation may change, but seeking habitats for population growth is not an option. In fifty years we have launched about 500 individuals into space, or several thousand if you count people with multiple trips. Human population growth is about a quarter million per day. That means you send Birmingham to Alpha Centauri today, Fresno tomorrow, Tacoma the next day... just to stay even.
And incremental growth won't cut it. We didn't send ships ever farther into the Atlantic. Columbus went across in one shot. We didn't go a quarter of the way to the Moon, or halfway. (Actually, our first few probes did, but only because we didn't give them enough velocity) Once the technology exists for a long voyage, the only sensible approach is to do it all at once. But we won't go to the stars until we have the capability: propulsion, life support, all of it.
CollapseWe've dodged a bullet in terms of nuclear apocalypse, at least for now. That's not to say we won't have a future superpower ruled by suicidal lunatics. Picture Brazil, say (just to pick a current non-nuclear major power) ruled by a North Korea style government and possessing a nuclear arsenal. Or ruled by an apocalyptic religious cult. But at least we aren't currently preoccupied with nuclear annihilation. What seems more likely to cause our collapse is environmental: exhaustion of resources, mass extinction, resurgence of epidemics, collapse of agriculture, and so on.
It's not inevitable that an alien race would suffer collapse. But it is all but inevitable that a race that has a blind faith in unceasing growth will collapse. If they have our brand of technological optimism, they won't take action until absolutely necessary, confident that new technology will present a solution to their problems. And they'll always be right. Until that one time they're wrong, and they make that one fatal miscalculation. After all, you can run a hundred red lights in a row without harm. It's that one time that causes the problem.
There's an argument called the Doomsday Argument that holds that the end of the human species is probably near. Any given person has an equal likelihood of being born at any point in human history, and the average position would be halfway through. Since about 100 billion people have already lived, we should expect roughly 100 billion more to come after us. Since global births now number about 134 million a year, it takes about 7-1/2 years for a billion people to be born, or about 750 years for the next 100 billion people to be born. There are tons of things wrong with this argument, chief among them the fact that we are where we are, and if we're at the 10% or 90% points, no amount of probability will change that. It's like arguing that most cars run fine, so the probability is that yours does too, and that clanking sound is just your imagination.
It might well be that the real Cosmic Filter is cultural. Once a civilization accomplishes what it can easily do in space and acquires most of the easily available knowledge, any further improvement might require such a huge additional investment that the effort seems unwarranted.
An additional collapse scenario is that sufficiently advanced civilizations may have their needs taken care of by machines so well that they lose the ability or desire to do things for themselves. Think of the progression of starship captains portrayed in Wall-E, each progressively tubbier and less motivated than the last. Imagine a civilization with holodeck technology but no interstellar travel. If they can visit any imaginable world without leaving home, why leave home? Our own concern with the environment and preserving history is laudable, but it bears an ominous resemblance to the renewed affection a child feels for an old toy just before giving it up forever. If you can see a tiger or a panda in virtual reality, why do we need the real thing? If you can go to Mars in virtual reality, why go for real? In short, they become Eloi. And watch the 1960 version of The Time Machine (the good one) to see just how contemptible the Eloi were.