Two years ago, in a column I wrote for Nanotechnology Now, I offered a basic explanation of the Fermi Paradox. As my ideas have circulated on the Web, they have generated a good number of comments, including objections to my reasoning and counter-proposals for our apparent isolation in the cosmos.
But I’d submit that no one has yet come up with any objection or explanation that makes more sense than what I have proposed.
To review, here is the starting point.
We Are Alone
As far as we can tell, we are alone in the universe. That is, human beings are the only technologically-advanced species for whom we have any evidence.
This observation is known as the Fermi Paradox. In 1950, the physicist Enrico Fermi famously wondered, "Where is everybody?" He was referring to the strange silence in the universe, the apparent lack of any advanced civilizations beyond Earth.
Fermi reasoned that the size and age of the universe would indicate that many technologically advanced extraterrestrial civilizations ought to exist. However, this hypothesis is inconsistent with the lack of observational evidence to support it.
So, where is everybody? Nowhere, it seems, or at least nowhere that we can detect.
Many explanations have been offered for this conundrum, with none coming even close to finding consensus. Physicists, astronomers, and philosophers are as far from answering the question today as when Fermi first posed it.
Perhaps the most disturbing aspect of the Fermi Paradox is what it suggests for the future of our human civilization. Namely, that we have no future beyond earthly confinement and, quite possibly, extinction.
But why should that be? Don't we have a potentially limitless future, with a solar system and eventually a galaxy waiting to be explored and settled?
It would seem so, and yet, the available evidence may suggest otherwise.
Three Propositions
If there are no other advanced civilizations detectable, it must mean one of three things:
1. We are the first intelligent beings capable of expanding into the cosmos and making our presence known. There have been no others.
2. There have been others before us, but all of them, without exception, have chosen -- or somehow been forced -- to expand in such a way that they are presently undetectable by our most sophisticated instruments.
3. There have been others, but all of them, without exception, have run into a cosmic roadblock that either destroys them or prevents their expansion beyond a small radius.
The first proposition, that we humans are unique and special, appears quite absurd. It contradicts all that we have discovered during the last five hundred years about the true nature of the universe and our place in it.
We are not special: the Earth is not at the center of our solar system, the solar system is not at the center of our galaxy, and our galaxy is not at any special position in the universe. Our placement in space and time seems to be random and unremarkable.
Moreover, we humans, along with every other form of life, have evolved to our present state in accordance with natural selection. There's nothing special about us.
Why, then, would it even be conceivable that earthlings are destined to be the very first species to make a noticeable mark on the universe?
If we reject proposition 1, then we must choose between propositions 2 and 3.
There is a crucial distinction between the second and third propositions. The former relies on choice, while the latter implies restriction by some force or law of the universe.
It seems strange to imagine, as suggested by proposition 2, that all extraterrestrial civilizations would, without exception, choose to expand or exist in such a way that they are completely undetectable to us. If proposition 2 is correct, it requires every one of potentially hundreds, thousands, or even millions of advanced worlds to make the exact same decision. We might expect some to do so, perhaps even most, but all? That defies logic.
So we are left with the third answer. Whatever civilizations have come before us have been unable to surpass the cosmic roadblock. They are either destroyed or limited in such a way that absolutely precludes their expansion into the visible universe. If that is indeed the case -- and it would seem to be the most logical explanation for Fermi's Paradox -- then there is some immutable law that we too must expect to encounter at some point. We are, effectively, sentenced to death or, at best, life in the prison of a near-space bubble.
Okay, so that sums up the problem. We are all by ourselves, as far as we can tell, and the explanation that seems to fit best leaves us stuck inside an expansion boundary from which we can never escape.
But now let’s take a look at some of the objections that others have made to my reasoning. Here are a few popular favorites.
Ascension: After a certain point, technologically advanced species move out of the physical realm and into a digital “virtual” existence, living it up forever inside a Jupiter Brain or its equivalent. We can’t see them and they don’t care about us.
Apathy: Similar to the Ascension explanation, the idea here is that species who are smart enough and technologically advanced enough to galactically expand don’t care to. They are happier writing poetry, listening to music, playing video games, or whatever.
Caution: Advanced species realize that human beings are dangerous, that we are psychotic, or that we are too immature for their kind to mess with.
All three of the above objections fall prey to the “everyone does it” fallacy. In order for them to be correct, we have to make the unsustainable assumption that every single technologically advanced species acts the same way. They would all have to make the choice not to expand or not to contact us, and that defies the logic of probability.
Bigness: The universe is so big and the distances involved so vast that all those other advanced civilizations simply haven’t had time yet to reach us. Related to this is the “needle in a haystack” explanation, suggesting that we just haven’t looked in the right place yet. Our SETI scans are not sufficient to do the job.
Fermi himself immediately dismissed this explanation with some quick back-of-the-envelope calculations. Given a reasonable estimate for how many habitable planets there should be and how long the universe has been in existence, it’s easy to determine that if there are any expanding civilizations, there must be many, and that they have had more than enough time to cover the necessary distances. Size is not the problem. We need a different answer.
Difficulty: Expanding into the universe is too hard, requires too much energy, is too expensive, or for whatever reason is not seen as worth the effort.
Again, for this to be correct, you have to assume that every single candidate species makes the same choice to forgo expansion. And if it’s not a choice, but simply a reflection of reality -- if expansion is so difficult that it’s effectively impossible -- then that proves my original proposition 3.
Invisibility: They’re there, but we just can’t see them. Our instruments aren’t able to detect them even though the evidence is basically right in front of us.
No, that explanation doesn’t work either, and for basically the same reason. It supposes that all advanced civilizations use the same kind of invisible-making technology. Some of them might, or most of them, but every single one?
Rareness: We might not be totally alone, but the number of intelligent species is so few, and the number of advanced technological civilizations so many fewer still, that we are like two or three tiny krill swimming inside an otherwise empty ocean. There is almost no hope that we will ever find each other.
Perhaps, but then you’re getting perilously close to making us “special” again, if not unique.
All in all, it seems clear to me — irrefutably logical — that some sort of cosmic roadblock, as yet unidentified, must exist. Either that or we are in a simulation.