I’ve always been skeptical of the E.T. hypothesis, which posits that some UFOs are likely aliens. The lack of hard evidence puts a low ceiling on its plausibility, and even mass sightings can have prosaic causes.1 But what about the occasional barn burner of a sighting, one with credible witnesses and backed by compelling video or radar data? What about the USS Nimitz encounters, for example?
Implausible does not mean impossible. UFO sightings are frequent enough, and their potential implications large enough, that smart people should be studying them. But many skeptics have a key objection: the Fermi paradox. The Fermi paradox argues that the apparent deadness of outer space contradicts the possibility of aliens, who would leave visible traces of their expansion, such as by dumping nuclear waste into stars, gobbling up the energy spumes from quasars, or rearranging galaxies in structured ways.
People have sought to reconcile the Fermi paradox for decades, such as by hypothesizing that aliens are hiding from each other, or that they have confined us to a cosmic zoo with a fake night sky. Unfortunately, most of these hypotheses grant aliens whimsical motives or godlike coordination capacities, when the more Occamic explanation is that they don’t exist.
Does that mean the Fermi paradox makes the E.T. hypothesis untenable? Maybe not. Here are two explanations that might reconcile the two arguments. The first is one I’ve heard before, but the second, I think, is original.
1. A Very Early Great Filter
Life looks to have arisen very early in Earth’s history. But what if it arose even earlier, such as in the stellar nursery of which our sun was once a part? If the emergence of life is very difficult, perhaps only occurring in stellar nurseries under rare conditions, then those nurseries might be where the Great Filter lies.2 The entire visible universe might therefore be dead—except for in those star systems that descended from that one stellar nursery, and wherever the life in the systems has since moved to.
If this model is true, the Fermi paradox is a little easier to reconcile, because we can rule out life being visible at certain orders of magnitude, given how long it would take for it to spread from its stellar-nursery origins in the Milky Way. We still have to wonder why local ancient civilizations3 wouldn’t be visible at other orders of magnitude—but, in dealing with just a few such civilizations, we have more room for whimsical equilibria that wouldn’t make sense at the largest scales, including ones where quirky cultural barriers have prevented those civilizations from expanding much.
The UFOs visiting us, if we grant that they are aliens, might therefore belong to our distant cousins, who have colonized but a few patches of the Milky Way yet remain eons from cosmic visibility.
2. A Not-Soon Future Great Filter
A common explanation of the Fermi paradox is that the Great Future lies in our future. That is, civilizations inevitably destroy themselves. They stumble onto some spectacularly dangerous technology, or they succumb to war or resource exhaustion or something else. This explanation seems unlikely, but it doesn’t scuttle the E.T. hypothesis. In fact, a future Great Filter dovetails with the E.T. hypothesis quite well.
That may seem counterintuitive. A common view among longtermists is that transitioning from a planetbound civilization to a spacefaring one will slash our existential risk; asteroids, supervolcanoes, and other hazards that could smite our now-uniplanetary species will no longer hang over us like Swords of Damocles. And risks to multiplanetary species, such as gamma-ray bursts, are rare enough that we can quickly spread beyond their reach. This thinking has merit. Certainly, scattering our species, knowledge, and infrastructure as far as possible cuts our exposure to the local hazards we face now, and the bulk of the Great Filter, if it lies in our future, might well precede interstellar expansion.
But the Great Filter might lie further ahead, in the era of interstellar expansion itself. We can’t yet know what risks we’ll face then. Maybe there are no cheap defenses against relativistic weapons, so that space colonists never get lasting footholds on other worlds before they’re obliterated by their enemies. Maybe expansion via von Neumann probes is much harder than we think, leaving species vulnerable to resource exhaustion before they can spread far. Models of spacefaring civilizations, especially in science-fiction, tend to view offworld colonies as seeds containing sufficient knowledge and infrastructure for further expansion. But such colonies might rely on resource inflows from their homeworlds for a long time before they can send viable seeds of their own.
Put metaphorically, perhaps a civilization’s spacefaring adolescence—instead of its spacefaring infancy, such as we are in now—contains the greatest barriers to attaining full technological maturity. If that’s so, encountering weak hints of alien civilizations, such as UFOs, is more probable than seeing their megastructures in the night sky. Those UFOs might represent the technological peak of almost all civilizations, combining the fantastic speeds and accelerations we expect of technology beyond our own with the clumsy behaviors and hide-fails we expect from a civilization that has not yet had millions of years to perfect its art.
If this model is true, our universe contains countless interstellar civilizations that occasionally bump into each other, and maybe even coalesce from time to time, before contracting into permanent quietude due to cosmic costs or hazards.
In a recent article contending that we should keep an open mind about UFOs, economist Tyler Cowen wrote: “to this observer, the most likely resolution of the Fermi paradox is this: The aliens have indeed arrived, through panspermia — and we are they.” Many people agree with Cowen that the E.T. hypothesis itself reconciles the Fermi paradox, but I’m not one of them. Rather, the Fermi paradox becomes more puzzling when you consider that aliens who can visit us haven’t also left a mark in the stars–unless those aliens are very rare, due to sharing our fluky stellar-nursery origins, or because they don’t survive their spacefaring adolescence.
1In 1909, businessman Wallace Tillinghast falsely claimed that he’d invented a new kind of airplane but would only fly it at night to prevent rivals from copying its design. Over the next fourteen months, thousands of people claimed to have seen the airplane in the night sky. H.P. Lovecraft, no easy mark, encountered a crowd of awestruck witnesses to one supposed night-flight, and saw that the object of their attention was Venus.
2The Great Filter is just whatever prevents dead matter from becoming a cosmically visible civilization.
3Why ancient? The universe is 13.7 billion years old. Adopting the mediocrity principle, we should not a priori assume we are early arrivals to the cosmic scene. Any true early arrivals would’ve had billions of years to leave a mark on the universe–plenty of time to do so, unless the costs and timescales of expansion are far, far higher than seems likely now.