I was reminded of this question by something or other today. It is the question that Enrico Fermi raised about the absence of any alien contact. Given the number of Sun-like stars in the Galaxy, any reasonable estimate of the probability of habitable planets around those stars, any reasonable estimate of the likelihood of life evolving, and most estimates of the probability of intelligent life evolving, it seems that there should be many, many civilizations out there. So, where is everybody?
In early science fiction, especially science fiction from the Forties and Fifties, which I read growing up, the answer seemed more or less obvious: they aren’t there because they all destroyed themselves through nuclear war, as it appeared likely that the human race would destroy itself. In the Sixties and into the Seventies, the answer still seemed obvious: if they didn’t destroy themselves through war, then they destroyed themselves through ecological disaster.
By the time I read those stories, it seemed less obvious to me that every intelligent species would destroy itself. After all, if war or ecological disaster threatened, shouldn’t reasonable beings start setting up colonies off their home planet? Colonies that could survive, with however much difficulty, regardless of what happened back home? So the question remained, where is everybody?
But then, one day I heard someone say, “If we can put a man on the Moon, why can’t we do X?” and someone else answered, “But we can’t put a man on the Moon today; we don’t have the resources.” I don’t remember the exact context because my mind instantly wandered to this: Here may be the explanation to the question of “where is everybody?”
It occurred to me that the Earth is probably unusual in a couple of ways. For one, it has two continental masses: the Old World, which is Eurasia plus Africa, together with the island of Australia (not normally included, but it is for my purposes); and the New World, the Americas. The intelligent species (there were a group but they were all closely related and we are the only survivors) arose in the Old World and spread out over it. This is why I include Australia as part of the Old World, since human beings reached it about 70K years ago.
Over time, the intelligent species developed more and more advanced technology, which they used to extract and utilize more and more resources. With more and more resources, the population grew and grew, and more and more resources had to (and have to) be devoted just to keep all the population alive. Every advance in technology, every new resource discovered, produced a population increase that ate up all the new resources, so that the average person was no better off, and often less well off, than their ancestors had been.
But then, there was the New World. Human beings had spread there too, but much later and with a very small founding population, so they had had a low technology base when they got there, and hadn’t had the same large population exchanging knowledge. So they had begun to use up their resources, but to a comparatively small degree. And then the advanced civilizations of the Old World happened upon the New World. Suddenly they had a massive, instantaneous influx of resources, without the population growth that had always accompanied the slow resource increases in the past. Suddenly, for one of the few times in history, there could be civilizations that were truly wealthy, that is, that had far more resources than people. This was a civilization that might be able to expend the resources to travel to another astronomical body.
And that brings me to the second way in which the Earth is probably unusual. We have the Moon. It is big and it is, relatively speaking, close. It has lots of resources, even water, which had long been expected and was recently proven. It has a respectable gravity, so although living there would take some adjustment, it would take a lot less adjustment than would be needed for a satellite like, say, Deimos. We could have established a colony there and from there spread out into the Solar System and ultimately perhaps to the stars.
Could have. Forty years ago perhaps we could have. But forty years ago the Earth’s population was less than three billion and now it is pushing seven. Population has grown to absorb all the resources of the New World, and, as any number of people have been pointing out during the Copenhagen Conference, our descendants will be far poorer than ourselves.
We don’t have the spare resources anymore, and it seems probable that we never will again. We had a chance — a sudden massive influx of resources into a relatively technologically advanced civilization, and a nearby satellite that is almost perfect for colonization — and we blew it. We will never reach the stars.
Other civilizations, on other planets, likely didn’t have the Old World/New World split, so they had probably filled up their entire planet by the time they developed enough technology to think of reaching for the stars, and they never had the spare resources. Even if they had, they’d likely have been looking at either colonizing a tiny satellite like Deimos, or making a big jump equivalent to a Mars shot as their first extra-planetary trip. Either way, they couldn’t do it.
Where is everybody? Trapped on their planets forever.
Just like us.