How Thinking about Aliens Reveals the Limits of Our Knowledge
published during a waxing crescent moon.

Two weeks ago, the Breakthrough Listen project, a $100 million venture aiming to find evidence of extraterrestrial intelligence, released their initial results. Using three powerful radio telescopes, the project spent two years scanning 692 nearby stars for the types of electromagnetic emissions that could only come from a technological civilization like ours. Despite finding a handful of compelling signals, Breakthrough doesn’t believe it has eavesdropped on ET’s phone calls quite yet.

A few days earlier at the Cambridge Science Festival in England, Seth Shostak, the Search for Extraterrestrial Intelligence (SETI) senior astronomer, reiterated why the hunt for aliens has predominantly focused on specific radio frequencies. Shostak believes that advanced extraterrestrial civilizations develop radio wave technology 100 percent of the time.

Shostak is a smart guy, as are many folks behind the Breakthrough Initiative and SETI. But there are few things we should be 100 percent certain about, particularly when it comes to complex processes like technological development. Yet ever since astronomer Frank Drake investigated a sliver of the radio spectrum coming from the stars Tau Ceti and Epsilon Eridani in 1960, we’ve been looking for intelligent beings on other worlds in pretty much the same way; using radio telescopes. Different search techniques get proposed every once in a while; during the talks at Breakthrough, astronomer, Shelley Wright, suggested watching for powerful infrared laser pulses and other researchers have recently argued that we should be using neutrino detectors to look for signals—but they all share a common bias. They are based on specific things that humans have discovered about the cosmos.


CSIRO’s Parkes radio telescope. Photo, taken in 1969. Credit: CSIRO

Science is an attempt at transcendence. Its methods were developed to produce knowledge that is not tied to the subjective experience of any one particular human being. An atom’s properties should be the same no matter who is doing the measurements. But what about science itself? Are the answers it produces completely objective; free of errors, preconceptions, or the accidental twists and turns of history? In trying to imagine the state of an alien society’s science, we are almost immediately confronted with the question of how we know what we know. A stroll through intellectual history should show that, at any given time, we would do well to remember both our knowledge and our vast ignorance.

A double tale I’ll tell. At one time one thing grew to be just one

from many, at another many grew from one to be apart.

Double the birth of mortal things, and double their demise.

Union of all begets as well as kills the first;

the second nurtures them but shatters as they grow apart.

And never do they cease from change continual,

at one time all uniting into one from Love,

while at another each is torn apart by hate-filled Strife.

Thus begins a fragmentary treatise from around 450 BC written by the Greek philosopher, Empedocles. He’s the guy Aristotle credits with first realizing that the universe is composed of four elements—earth, air, fire, and water. In Empedocles’ teachings, these four eternal equally-balanced fundamentals are constantly arranged and rearranged by two active forces, a creative one he calls ‘Love’ and a destructive one he names ‘Strife.’ Every object and being in existence is subject to this cosmic cycle of birth and death. Though one could argue that aspects of it remain partially accurate, Empedocles’ poetic philosophy is rather far from the mark of being right, especially when compared to our modern understanding of how the universe works. Yet some of his basic tenets held sway for nearly 2,000 years.

People in the past weren’t necessarily less intelligent than us; they simply had different concepts and criterion for judging what is true. The longevity of Empedocles’ incorrect ideas had to do with the fact that scholars continued to find them useful tools for approaching the study of reality. The four-fold theory of matter was successful. It explained much of what was known about the universe at the time. Empedocles even did experiments, inverting a bucket of water and noticing that a pocket of air remained trapped inside, proving (to him) that air and water were different substances. Aspects of his teachings made their way into subsequent theories of inquiry, such as alchemy.


The Greek philosopher, Empedocles, who believed the universe Alchemy, of air, water, earth, and fire. Source: Thomas Stanley, The history of philosophy, 1655

Nowadays, we think of alchemy as little more than an attempt to turn base metals into gold but, as chemist and historian of science, Lawrence M. Principe, traces in his book The Secrets of Alchemy, it was, in fact, a sophisticated research program guided by an intellectual framework that we no longer entirely understand. For instance, in 800 AD, the Arabic city of Baghdad was one of the centers of learning of the world. Passages from a scholar named Jabir written around this time discuss the production of elixirs for transmuting metals into gold. Back then, there were only seven recognized metals: copper, iron, tin, lead, mercury, silver, and gold. Jabir posited that each was composed of precise mathematical ratios of four different qualities—hot, dry, cold, and wet—a system that derives from the Greek physician, Galen, who based his ideas in part on the theory of the four classical elements. To turn any metal into gold, you just had to introduce the right amounts of hot, dry, cold, and wet until its ratios were identical with that of gold.

Now here’s where it gets really complicated. Jabir asserted that the ratios of the qualities in each metal can be divided into seven grades. He then created a four by seven table, placing the 28 letters of the Arabic alphabet in each box. To know how much ‘hot’ there is in a substance like lead, one must look at each letter of the Arabic word rub (lead) and analyze it using the chart. The first letter of lead is alif, which is in the box with the highest grade of ‘hot.’ So lead contains the highest grade of ‘hot.’ Therefore, to turn lead into gold, one must dial down the amount of hot it contains until its proportions line up with that of gold.

The system seems arbitrary to us, but it didn’t to Jabir. His ratios are all based on significant numbers from the time, the equivalent of Planck’s constant or the speed of light to a modern physicist. And Muslims believe Arabic to be a divine language; its words are God’s true words for objects in the world. Analyzing the name of something using Arabic letters was considered a fruitful way to reveal important properties about it. Though Jabir was quite wrong in the inner workings of metals, his use of logic and reasoning based on the things he knew is recognizable to a modern researcher.


An engraving of the tools used by the Arabic alchemist, Jabir. Source: Popular Science Monthly Volume 51

“People today and people of the past often do not share the same vision or expectation of the world, nor do they necessarily approach the world in the same way,” writes Principe. “Their questions were not our questions, nor were their ways of answering them necessarily our ways. What seems arbitrary to one expresses a profound law of nature to the other; what seems an insight into the design of the cosmos to one appears as mere trivia to the other. Recognizing these differences helps us avoid the error of projecting our own knowledge and expectations onto the past as measures of its value.”

Today, we believe the universe is comprised of subatomic particles that interact using four fundamental forces. But in the history of ideas, this is a relatively young model. Electromagnetic radiation was officially discovered in the 19th century; neutrinos were first postulated only 80 years ago. What are the chances that we will discover nothing new about either in the next few centuries, perhaps something that might radically alter our understanding of these basic phenomena? Neutrinos could one day prove to be an illusion created by an incomplete reading of reality, much like the four classical elements or the seven recognized metals of previous eras. SETI practitioners often posit receiving a message from a civilization that has been around for hundreds of millions of years. But in trying to imagine an alien civilization far older than ours, we have to remember how strange our own ideas sound after a mere millennia or two.

A scene from the film, Arrival (2016), depicting an alien communication system entirely unlike our own.  Credit: Paramount Pictures

Of course, people like Shostak may argue that you can’t compare theories from a pre-scientific time with those that came afterward. Our current conjectures are underpinned by sophisticated mathematical equations and verified by reams of experimental evidence. And maybe intelligent extraterrestrial civilizations spend a great deal of time producing bogus ideas like alchemy before stumbling on the perfection that is science, which generates objective truths that remain in place for the ages. But the history of our being wrong should at least raise the possibility that we don’t quite have it all figured out now either. Science makes its own missteps in the pursuit of understanding, coming up with false theories that are eventually overthrown as new evidence accumulates.

Epistemology—the study of why we know what we know—must go hand in hand with agnotology—the study of why we do not know what we do not know. For instance, we can never truly know when we have learned all the important things about the universe. Even if researchers one day announced, “we have discovered everything there is to discover,” how could we actually be certain of that? Reality does not come with little labels denoting what is important and, the next day, some new significant finding might rear its head.

“The answers you get depend on the questions that you ask,” wrote the historian of science Thomas Kuhn in his famous book The Structure of Scientific Revolutions. Our understanding of atomic forces relies on particular theoretical frameworks and the instrumentation we have built to validate them. Could the history of humanity’s knowledge have gone in some other direction? Perhaps out in the universe, there exists another civilization that has discovered a few of the millions of things that we do not yet know.

“While it may be true… that the structure of atoms does not depend on who studies them, scientific models of atoms may be very much influenced by the characteristics of the scientists who construct these models,” writes psychologist Douglas Vakoch in his 1996 paper, Iconic approach to communicating chemical concepts to extraterrestrials.  “And when two scientists differ in biology, culture, and history as much as humans and extraterrestrials would differ, these models of reality may vary considerably.”


Even on this planet, intelligence comes in a surprising diversity of forms. Octopus opening a jar. Credit: Matthias Kabel

Vakoch calls the possibility that we couldn’t understand the scientific theories of another species the “Incommensurability Problem”—the idea that alien minds will be geared toward such different things than our own that we will struggle to even recognize what they are talking about. It’s not the only possibility; given enough time, maybe all species converge on the same “true” answers about the universe. But in an infinite and diverse cosmos, it’s also conceivable that the gulf between our concepts might remain forever uncrossed. The environment and senses of intelligent extraterrestrials will no doubt influence their understanding of the world in important ways.

At this point, we are not looking for anything other than ourselves.

“A society of porpoises might lack crystallography but develop a very sophisticated hydrodynamics; one comprised of molelike creatures might never dream of developing optics or astronomy,” writes philosopher Nicholas Rescher in The Limits of Science. “One’s language and thought processes are bound to be closely geared to the world as one experiences it. As is illustrated by the difficulties we ourselves experience in bringing the language of everyday experience to bear on subatomic phenomena, our concepts are ill-attuned to facets of nature different in scale or structure from our own. We can hardly expect a science that reflects such parochial preoccupations to be a universal fixture.”

Both SETI and Breakthrough Listen rely on the idea that extraterrestrials will reach relatively similar technological and scientific stages as us. Really, that’s the only thing they can do. Once you abandon that premise, their research program disappears as well. This doesn’t mean listening to radio signals from space is pointless (after all, I might be wrong). We just shouldn’t take the fact that we haven’t heard anything as too meaningful. Right now, it’s like we’re listening for distant drumbeats through the forest while alien civilizations might be flashing bioluminescent lights at the bottom of the ocean. Though it’s impossible to imagine the truly unimaginable, we should recognize that we have yet to take the steps necessary to conceive of realistic alien civilizations. Our ideas remain rather egocentric; at this point, we are not looking for anything other than ourselves.


Illustration from Conversations on the Plurality of Worlds.

The French writer, Bernard le Bovier de Fontenelle, published a book in 1686 called Conversations on the Plurality of Worlds in which a gallant philosopher and a beautiful marchioness walk through a garden at night, conversing. Between flirting, the two talk about the latest scientific theories, such as the heliocentric model of Copernicus and the possibility that men live on the moon. At one point, the marchioness asks what sort of creatures these moon men might be. “Upon my word,” replies the philosopher, “I can’t tell.”

“Were it possible for us to be endowed with reason, and at the same time not of the human species; were we, I say, such beings, and inhabitants of the moon, should we ever imagine that this world contained so fantastical a creature as man? Could we form in our minds the image of a being composed of such extravagant passions, and such wise reflections; an existence so short, and plans so extensive; so much knowledge of trifles, and so much ignorance of the most important things; such ardent love of liberty, yet such proneness to slavery; so strong a desire for happiness, with so little power of being happy? The people in the moon must be very clever to imagine such a motley character. We are incessantly contemplating our own nature, yet we are still unacquainted with it.”