--Enrico Fermi, 1950
If we subscribe to the conventional interpretation of the Fermi Paradox (a thought experiment that forces us to struggle with the prospect of a Cosmos largely devoid of intelligent life), it would seem we're indeed alone, at least insofar as we have any hope of making contact with interstellar neighbors. But what exactly is the Fermi Paradox? And does it necessarily imply that we're a freak of stellar and biological evolution, potentially the only intelligent species in the universe?
Physicist Enrico Fermi's vaunted "paradox" began as an off-the-cuff thought experiment. If the galaxy is suited for the emergence of life and intelligence, Fermi asked, then why do we fail to readily detect the handiwork of extraterrestrial species? After all, according to the wisdom of his era, expansion into space seemed near-inevitable. And if humans were poised to become a multi-planet species, then certainly aliens had accomplished the same feat long before we arrived on the stage, perhaps transcending their home solar systems in favor of interstellar colonization and mind-boggling feats of "astro-engineering." (Fermi would probably have been hard-pressed to imagine an early 21st century bereft of Mars colonization, let alone the demise of the Apollo program.)
Today, Fermi's query has attained the status of a cosmic statute, especially among theorists convinced that intelligent life is witheringly rare. Proponents of the Anthropic Cosmological Principle, for instance, believe the universe shows unmistakable evidence of existential "fine tuning," presumably to allow the existence of human life. (An engaging alternative is that the universe is as we perceive it because, if it were otherwise, its history would have precluded our evolution and we simply wouldn't be here. More recently, cosmologists have speculated that we might inhabit a "multiverse" comprised of an infinite number of universes, all governed by variations of the laws of physics as we know them. If such is the case, we shouldn't be especially surprised to find that physical laws seem "fine-tuned" for our existence, as our universe would be one of many: a cosmic jackpot well within the realm of probability.)
Despite the emphasis routinely placed on Fermi's famed quip, there's no evidence that Fermi himself ever intended it to be anything more than a useful thought experiment. He wasn't condemning the existence of extraterrestrial intelligence so much as speculating on the form alien intelligence might take -- and challenging his colleagues to devise ways in which potential civilizations might be detected.
In many important respects, Fermi's challenge has been neglected by science; we have yet to rise to the task of envisioning truly alien aliens. Too often, the extraterrestrials envisioned by SETI researchers are little more than simple extrapolations of ourselves, encumbered by human priorities, human psychology and even human economics.
But even Fermi's hunch that intelligent species will in some way make themselves visible to us is necessarily anthropomorphic; in reality, extraterrestrials might have better things to do, even if they're very much aware of our presence. (As argued in prior posts, revealing themselves -- whether to us or to the galaxy at large--might prove incredibly silly or even fatal.)
In part, we long for hard evidence that we're not alone not because we want to know that our own civilization can endure the long, hard centuries to come. The evident silence that greets our radio telescopes, far from proof that our universe is unreasonably hostile to life or that aliens succumb to disasters of their own making, is a mute challenge. Fermi's question remains relevant -- just not in the way some experts would have us believe.
This piece originally appeared at aboutSETI.com.