Some say the story is apocryphal, but even uncorroborated tales are often instructive.
It seems that Enrico Fermi and some physicist pals were sitting around a lunch table in 1950, when Fermi suddenly blurted out "so where is everybody?"
That small statement hardly sounds remarkable -- it's the kind of thing I've said at fundraisers for fresh-water otters. But Fermi was no schlub -- he had won the Nobel Prize a dozen years earlier, and you can bet dollars to Doritos, he meant something deep.
His meaning seems to have been the following: A simple calculation (surely one that Fermi could manage between two bites of a sandwich) shows that colonizing every star system in our galaxy would only take a few tens of millions of years. Since the Milky Way is more than ten billion years old, what Fermi realized was that, if extraterrestrial life is commonplace, there's been more than enough time for an ambitious society to spread out and build their own United Federation of Planets. But we don't see any evidence for a galactic empire, other than on Star Trek re-runs. Does that mean that Homo sapiens is the smartest species within 100 thousand light-years?
That would be remarkable and, judging by my daily interaction with said species, scary. I have always thought it much more likely that the cosmos is replete with thinking beings. After all, my day job is to look for them.
Reconciling an optimistic view of extraterrestrial intelligence with the failure to see any signs of galaxy-wide colonization has become known as the Fermi Paradox, a conundrum that has tempted the imagination of many people. The suggested explanations can -- and have -- filled books.
Just to give you a mini-sample: Some folks have opined that no aliens have colonized the galaxy simply because they inevitably blow themselves up in massive, hi-tech wars before completing the project. Others say that it's too expensive -- you can better stay home, and improve lifestyles in your natal solar system. A personal favorite of mine is the idea that the galaxy might be urbanized, and we happen to live in a largely empty, rural district.
The onset of the digital age has spawned other suggestions: Maybe truly advanced societies don't build big stuff -- honking interstellar rockets for boldly going to someone else's galactic quadrant. Rather, these sophisticated sentients start miniaturizing their technology, eventually uploading their minds into some sort of microelectronic computer, at which point colonizing star systems will seem as tempting as oxcart travel.
A more draconian explanation for why we don't see the trappings of empire is the suggestion that there really is no galaxy and no us. Everything we experience is just a software simulation run by someone as an experiment (or as an amusement). Our daily lives are no more than computer code. And the rules of this giant matrix-like existence forbid contact -- just because.
Fermi's remark continues to pique our imagination, and explanations for his provocative question keep popping up like whack-a-moles. Last month, two researchers in the Ukraine, Igor Bezsudnov and Andrey Snarskii, reported on a computer simulation in which galactic civilizations randomly arise, spread out to a greater or lesser extent, and then -- eventually -- fail and fall. As a time-lapse movie, this would look something like raindrops hitting a pond. Splashes would occur here and there, generating brief waves of local colonization. But eventually each splash would dissipate and die. Well, there's nothing new in this -- the model is just saying that every culture has a finite lifetime. But the Ukrainian scientists added a twist: if two civilizations chanced to overlap in time and space, the resulting contact would give the merged society a longer lifespan. In other words, the researchers assumed that meeting the neighbors was ultimately good for you.
When the simulation was run, it turned out that in some cases (depending on the birth and death rates of societies, not to mention the degree to which they could be mutually beneficial) a galaxy-wide society would emerge. A galactic federation. The authors of the study claim that their work gives insight into Fermi's Paradox by suggesting that either the Milky Way doesn't produce sophisticated societies very often (in which case, we're largely alone), or that it's still too soon to expect a pangalactic empire.
While interesting, the Ukrainian work certainly hasn't satisfied those who are dismayed by the lack of Klingon colonists as far as the eye can see. In the end, of course, the only way we'll resolve Fermi's notorious, sixty-year-old puzzle is to find the aliens, if they're out there. I suspect Fermi probably felt the same way. He doesn't seem to have continued the conversation over dinner.