Where do aliens come from? They won't arrive on spaceships

And whether they come through wormholes, or teletransportation, or some other means, it is most probable that what will count for them as “arrival” will not be an arrival in an organically embodied form. Indeed, the idea that alien visitors would come in biological bodies such as ours is, I contend, even less plausible than that they would come in artificial contraptions. Organic substrates, as the philosopher and xenobiologist Susan Schneider has argued, may well turn out to be a relatively short-lived host for intelligence whenever and wherever it emerges in the universe, soon to be replaced, wherever a technologically advanced species appears in the cosmos, by robots.

If intelligent beings are smart enough to get here, they are almost certainly smart enough to get here without dragging their bodies along. They could get around this hitch by transferring their consciousness or personal identity (whatever that is) into some more durable physical substrate — either a technological device of their own making, or, more intriguingly, a pre-existing physical system or process in the universe into which they figure out how to integrate themselves. To be clear, I have no clue how this would work. But neither you nor I have any idea how you could sit your living body down and fly a school-bus-like shuttle across interstellar distances — so the modal operator at work in both cases is not concrete feasibility, but only conceptual possibility.

Our alien visitors could also pull off such an impressive feat simply by means of what we, with our limited technological imagination, would classify as “simulations”. For us, when a high-powered telescope or an unmanned probe sends back images of objects in space, we consider that we are “seeing” and “experiencing” these objects only in a downgraded better-than-nothing sense, as mediated representations. But this may only be because our technologies of representation are still in a primitive stage, while another race of intelligent beings might well succeed in improving these technologies to the point where technologically mediated representation might count for them as “the real thing”. It might be both easier and more desirable for them to avail themselves of such representations than physically to travel and to experience that thing unmediated in a way that we ourselves, in our present technological condition, would consider “real”.

To imagine that one must go to another part of the universe, in one’s own organic body, in order to truthfully claim that one has been there, may turn out to be somewhat like supposing, circa 1920, that in order to participate in a conference with colleagues in Paris, one must actually go to Paris, rather than joining them by Zoom — a possibility that would only come onto the horizon a century or so later.

But let us suppose just for a moment that alien beings did set themselves the goal of making an “actual” voyage to Earth in their standard-issue, carbon-based, biologically evolved bodies. And let us suppose they succeeded. What might these bodies look like? There are at least some compelling arguments that any technologically advanced race of beings is likely to share certain anatomical traits with us: appendages that grasp, for example, or adaptations facilitating gravity-bound terrestrial locomotion. I have even heard it argued that space-travelling aliens would probably be equipped with exactly two eyes, and as with us, these would be found in the front of their faces, facilitating binocular vision.

We know from convergent evolution in widely different phylogenies on Earth that different species can come to have similar appearances (e.g., placental wolves in the northern hemisphere and marsupial “wolves” in Australia), and in principle, it is possible that xenobiological evolution could yield up bipedal, two-handed beings with eyes in the front of their heads. But wolves and “wolves” started from a common mammalian ancestor, and what you could not expect to find in any interstellar convergence of organic Baupläne is a being such as the one purportedly discovered of late in Mexico, which clearly has not just hands, feet, and a face, but also a ribcage, a spinal column, and an unmistakable pelvis. On Earth only about 3% of all animal species are vertebrates; how strange it would be if our first extraterrestrial visitors turned out to be vertebrates too!

But the really interesting question is why, in the first place, we started thinking about the beings that inhabit the world “up there” (call it the heavens, or the celestial spheres, or outer space, according to the conventions of your era) as similar to us in their bodily conformation, which is to say as organic beings.

This habit of ours has a very precise starting point in history. We could probably find some earlier examples if we tried, but I tend to date the birth of aliens, as we know them today, to 1609, the year Johannes Kepler wrote his Somnium (which would only be published posthumously in 1634). This is a peculiar work, both a proto-science-fiction reverie, as the Latin title suggests, and a work of properly modern relativistic astronomy, in which the author attempts to describe how the orbits of the other celestial bodies would appear if one were observing them from the moon. In the dream-like part of the work, Kepler relates the story not only of the transit of his hero Duracotus to our nearest satellite (evidently with the assistance of some psychoactive plants), but also the various animal-like beings he finds once he arrives there, including some creeping and slithering reptiles, and some sort of giant camel. Some decades later, in his Histoire comique des États et Empires du Soleil of 1662, the French author Savinien Cyrano de Bergerac would describe the different species of birds that inhabit the surface of the sun.

Why are we beginning to find birds, snakes, and camels in a region of the cosmos where previously we could have expected to find only spirituous beings, divinities, and angels? During this same period, natural philosophers such as René Descartes and G.W. Leibniz were intent on arguing for the uniformity of nature. The new mechanical philosophy required its adherents to accept the principle that, as Leibniz would put it: “Always and everywhere, it’s the same as it is here.”

For Descartes, it made no sense to divide the cosmos into different ontological realms, as the Aristotelians had previously done, where different laws apply to each. On the Aristotelian model, the most significant boundary in the physical universe is the one traced by the orbit of the moon: everything below it is a “sublunar” being, subject to generation and corruption (i.e. birth and death), while everything above it is immortal. In the new Cartesian physics, by contrast, the laws that govern the motions of bodies here on Earth, from the arc of a projectile shot from a cannon, to the rising and lowering of the tides, to the generation of a foetus, are exactly the same as the laws that govern the formation of other star systems, and presumably also of the planets and of the beings inhabiting them.

In other words, the key theoretical innovations of the scientific revolution positively require that, if there are intelligent beings elsewhere in the universe, they are like us. Specifically, this would mean that they depend for their existence not on some fine homogeneous ether or quintessence (as the celestial beings were often conceived in premodern cosmology), but rather on a specific arrangement of internal organs constituting a fragile and perishable organic body. In short, the homogenisation of the physical universe, which had been such a key part of the new mechanical physics, caused a corollary reconceptualisation of the inhabitants of the world “up there”, from quasi-divine beings that were either immaterial or ethereal, to ordinary reptiles or humanoids such as those that have remained the staples of science fiction, and of tabloid claims of alien sightings, to the present day.

Nearly all the great Enlightenment philosophers presupposed that other worlds must be inhabited by organically embodied intelligent beings like us. Thus Immanuel Kant declares in his Critique of Pure Reason of 1781: “I say that it is not merely an opinion but a strong belief (on the correctness of which I would wager many advantages in life), that there are also inhabitants of other worlds.” Kant’s sometimes-adversary, the significantly less rigorous Emanuel Swedenborg, wrote extensively of his own purported voyages to Jupiter and Saturn, where he learned a great deal about the inhabitants’ agricultural methods, the techniques they employ for yoking their beasts of burden, and so on. For more than 200 years, for serious and unhinged thinkers alike, outer space was teeming with a very familiar variety of life, not so different from the sort we know here on Earth.

By the late 19th century, just at the dawn of the era of rocket science, with actual space exploration finally within reach (Konstantin Tsiolkovsky would publish his “ideal rocket equation” in 1903), institutional science entered a sort of “alien winter”. I deploy this term in conscious allusion to the “consciousness winter” that hung over brain science for the better part of a century, scaring researchers away from any acknowledgement of the self-evident reality of internal subjective states of the mind.

In the same fashion, for most of the 20th century — notwithstanding Carl Sagan’s enthusiasm and the small budgets allocated for programmes like SETI — sober-minded experts placed a high premium on the public expression of scepticism about non-terrestrial intelligent life. Naysaying became part of the system of values and presuppositions by which the public identity of an expert was confirmed. In the same period, preoccupation with aliens mostly became the monopoly of fantasists of various sorts, either the creators of fictional entertainments or people who were unbothered by the social stigma of holding beliefs perceived to be “fringe”.

Why exactly this “winter” set in when it did has much to do with the broader cultural history of science and of the perception of expertise, and indeed seems not entirely separate from the long banishment of consciousness as a category of inquiry. Throughout the 20th century, for the most part, excessive interest in extraterrestrials was the telltale mark of a crank. This attitude had much to do with the reigning positivism of the scientific community, and the general consensus that speculation about things happening beyond the sphere of direct observability is ipso facto unfalsifiable and therefore unscientific.

But this era has decidedly come to an end in the past decade or so, as vast social, economic, and technological transformations have fundamentally realigned the public’s perception of expertise, and of who gets to claim to have it. After the crisis of epistemic authority that experts brought upon themselves throughout the Covid pandemic, and after the replacement of our old media ecosystem by one in which authoritativeness has become more than ever a sort of popularity contest, we are now in a period of history in which extraterrestrials are important if the masses of internet users think they are important, scientific consensus be damned. Under these conditions, the 20th century’s “alien winter” comes to look to many like a government cover-up. The truth is far more banal.

The cultural position of aliens has changed radically in the 21st century, both as a result of changes in the cultural position of science, but also as a result of real and promising scientific breakthroughs. Notably, since the Nineties, there has been a tremendous revolution in the way we observe, catalogue, and estimate the number of habitable exoplanets, and significant discoveries have also been made in astrochemistry, favouring the theory of so-called “soft panspermia”, according to which the chemical compounds that brought about the first life-forms on earth are by no means rare in the cosmos. Given these scientific advances, and given our new information ecosystem, it is safe to say that we will be hearing a lot more about aliens in the coming years. But we would be foolish to believe that this is the result of an actual uptick in sightings, or that our own most recent cultural representations of intelligent life beyond Earth get something uniquely right about the heavens that our ancestors failed to notice.