A Brief-ish History of METI. Part I: Early Ideas and Experiments
Long before modern astronomy gave us the tools to measure the cosmos with precision, humans looked to the stars and were profoundly astounded by what they saw. Even by the most ancient reckoning, the night sky offered more than enough to inspire awe and wonder, make us feel insignificant in the grand tapestry of existence, fire our imaginations, and foster a deep, almost spiritual sense of connection to something larger than ourselves. Yet, for as long as humans have surveyed the heavens with naked eye, telescope, and radio dish alike, they have seen no unambiguous indication that life as we know it exists elsewhere — a haunting phenomenon that has come to be known as the "Great Silence."
For many scientists and philosophers, the disparity between the assumed prevalence of life in the Universe and the profound lack of evidence for it raises a troubling incongruity often erroneously referred to as "Fermi's Paradox" — a label that, as we shall see, is neither entirely Fermi's nor technically a paradox. It seems like a valid and urgent question when you consider the facts. Given the age, size, and staggering density of the known Universe, shouldn't we have found unambiguous evidence of extraterrestrial life — and extraterrestrial intelligence — by now? The silence, in many ways, is the most deafening sound in all of science.
More than sixty years after the first Search for Extraterrestrial Intelligence (SETI) experiment — the legendary Project Ozma, conducted by Dr. Frank Drake in 1960 — scientists are still asking the fundamental question: "Are we alone in the Universe?" In addition to listening to the cosmos for radio signals and other signs of technological activity (collectively termed "technosignatures"), active efforts have been mounted to send messages out into space with the explicit purpose of making contact with an extraterrestrial intelligence (ETI). This practice has come to be known as Messaging Extraterrestrial Intelligence (METI), distinguishing it from its more "passive" SETI cousin. Today, we begin looking at the brief — ish — history of METI and how this bold, controversial, and deeply human endeavor came to be.
The Question That Started It All: Fermi's Famous Lunch
As the astrophysicist and science historian Paul Patton has carefully documented, Fermi's Paradox is named for the celebrated Italian-American physicist Enrico Fermi. In the summer of 1950, during an otherwise unremarkable lunchtime conversation at the Los Alamos National Laboratory — where Fermi had worked years earlier on the Manhattan Project — Fermi and his colleagues were casually discussing the recent spate of UFO sightings making headlines across the United States. It was then that Fermi posed a deceptively simple but staggeringly profound challenge, reportedly blurting out of the blue: "Where is everybody?"
After some characteristically rapid back-of-the-envelope calculations — a hallmark of Fermi's legendary problem-solving style — Fermi and his colleagues concluded that if interstellar travel were both feasible and desirable, Earth should have been visited by extraterrestrial civilizations several times over already. Even at a fraction of the speed of light, a sufficiently advanced civilization could traverse the entire Milky Way galaxy within a few million years — a cosmic eyeblink compared to the galaxy's age of over 13 billion years.
This line of reasoning eventually gave rise to the Hart-Tipler Conjecture, named after physicists Michael Hart and Frank Tipler. In a series of influential and controversial papers published between 1975 and 1982, they argued that this "paradox" could be resolved only by a stark conclusion: that extraterrestrial intelligent life simply does not exist elsewhere in the galaxy. Hart's 1975 paper in the Quarterly Journal of the Royal Astronomical Society was particularly blunt in its assertion, suggesting that the absence of extraterrestrial visitors constitutes strong evidence that humanity is uniquely alone.
Since then, many distinguished scientists — most notably Carl Sagan — have vigorously challenged this logic, arguing that there are innumerable plausible reasons why humans have not yet heard from intelligent life. Or as Sagan and William Newman famously articulated in their 1983 rebuttal:
"The absence of evidence is not evidence of absence." — Carl Sagan & William I. Newman, The Quarterly Journal of the Royal Astronomical Society, 1983
From this rich intellectual debate, the modern working definition of the Fermi Paradox emerged. It posits that the disparity between the assumed prevalence of life in the Universe and the lack of detectable evidence for it can be resolved by one of two broad postulates: either extraterrestrial intelligent civilizations do not exist in sufficient numbers to be detected, or special circumstances — physical, social, technological, or otherwise — exist that prevent us from detecting them. This framework, sometimes called the Fermi-Hart problem by more precise scholars, continues to drive SETI and METI research to this day.
Why the Universe Should Be Teeming with Life
The frustration underlying the Great Silence becomes even more acute when one considers the sheer scale and richness of the cosmos. The observable facts are nothing short of staggering:
- The Universe is Vast: While our observations are limited by the fundamental speed of light and Einstein's Theory of General Relativity, scientists estimate that the observable Universe spans approximately 96 billion light-years in diameter — and the full extent of the cosmos may stretch to infinity beyond what we can ever hope to see.
- The Universe is Extraordinarily Populated: A landmark 2016 study revised the estimated number of galaxies in the observable Universe to more than 2 trillion — ten times more than previously thought. These range from dwarf galaxies containing just a few thousand stars to colossal elliptical galaxies harboring as many as 100 trillion stars.
- The Universe is Ancient: Based on the most precise measurements of the Cosmic Microwave Background (CMB) radiation — the afterglow of the Big Bang — scientists estimate the cosmos is approximately 13.8 billion years old. This is an almost incomprehensibly long period during which life could have arisen, evolved, and developed intelligence across countless worlds.
- Exoplanets Are Everywhere: Data from NASA's Kepler Space Telescope and its successor, TESS, suggest that virtually every star in the galaxy hosts at least one planet. Billions of these planets reside in the habitable zones of their parent stars — regions where liquid water, and potentially life as we know it, could exist.
- The Ingredients for Life Are Universal: Life, as we know it, is built from a relatively small set of chemical elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur — collectively abbreviated as CHNOPS. Astronomical observations have confirmed that the Universe is remarkably homogeneous and isotropic on large scales, and that these life-enabling elements exist in abundance everywhere we look, from the interstellar medium to the surfaces of distant asteroids and comets.
An Evolving Name: From Active SETI to METI
Before diving deeper into the history of this discipline, a note on nomenclature is essential. Traditionally, scientists made no rigid distinction between SETI and what we now call METI, often pursuing both listening and transmitting projects concurrently and with equal enthusiasm. For instance, Cornell astrophysicist Dr. Frank Drake — who led the first SETI experiment, Project Ozma, in 1960 — was also central to the first true METI project roughly fourteen years later: the iconic Arecibo Message of 1974. Similarly, the celebrated science communicator and astronomer Carl Sagan, who became integral to early SETI efforts, later collaborated with Drake to create not only the Arecibo Message but also the Pioneer Plaques (1972–1973) and the legendary Voyager Golden Records (1977) — humanity's most elaborate and enduring messages in a bottle cast into the cosmic sea.
The specific term "Active SETI" did not emerge until 2005, coined to describe the deliberate act of transmitting messages into space intended for extraterrestrial recipients. The following year, Russian radio engineer and astronomer Alexander Zaitsev of the Institute of Radio Engineering and Electronics in Moscow went further, coining the term "Messaging Extraterrestrial Intelligence" (METI) to formally differentiate between listening and transmitting activities. As he wrote in his foundational 2006 proposal paper:
"Those who propose, or oppose, sending Messages to Extra-Terrestrial Intelligence (METI) must contemplate the Hamlet-like question: 'To send or not to send?' The science known as SETI deals with searching for messages from aliens. METI science deals with the creation of messages to aliens. Thus, SETI and METI proponents have quite different perspectives... METI pursues not a local, but a more global purpose — to overcome the Great Silence in the Universe, bringing to our extraterrestrial neighbors the long-expected annunciation: 'You are not alone!'" — Alexander Zaitsev, 2006
This terminological distinction, while seemingly academic, carries profound philosophical and ethical weight. The act of transmitting, as opposed to merely listening, fundamentally changes humanity's relationship to the cosmos — transforming us from silent observers to active, potentially vulnerable, participants in an interstellar conversation whose other participants we know nothing about.
Why Message at All? The Rationale for METI
In a significant follow-up paper released in 2011, "Rationale for METI," Zaitsev laid out METI's philosophical and scientific mission statement with compelling clarity. He quoted the work of American radar astronomer Steven Ostro, whose unpublished research had proposed the audacious idea of constructing a powerful omnidirectional radio beacon on the far side of the Moon — shielded from Earth's own radio interference — to broadcast humanity's existence to the galaxy at large. As Ostro eloquently argued: "We might conclude that it is better to give than to receive, and that the war on Great Silence must begin at home."
Among METI's most intellectually compelling justifications, Zaitsev highlighted what he termed the "SETI Paradox": the unsettling possibility that advanced civilizations throughout the galaxy hear only silence because everyone is listening and no one is transmitting. If every sufficiently advanced civilization adopts a purely passive, receive-only stance — perhaps out of caution, indifference, or resource constraints — the result is a galaxy-wide game of cosmic chicken in which first contact never occurs. In this scenario, the Great Silence is not evidence of loneliness, but of a collective failure of interstellar courage.
Zaitsev further observed a striking empirical asymmetry: previous SETI programs had collectively spent hundreds of times longer listening to space than METI experiments had spent transmitting. Yet it is transmission, not reception, that initiates true communication. The possible long-term benefits of interstellar communication — the sharing of knowledge, science, mathematics, art, and philosophy across the stars — were being systematically avoided by the passive-only approach. As Zaitsev provocatively argued, this enforced isolation could ultimately prove catastrophic for any civilization that adopted it:
"Isolationism as a possible cause of extinction of civilizations... Civilizations which are forced to hide and tremble because of farfetched fears are doomed to extinction." — Alexander Zaitsev, Rationale for METI, 2011
For readers familiar with Liu Cixin's celebrated Remembrance of Earth's Past trilogy — popularly known in the West as The Three-Body Problem series — Zaitsev's concerns will immediately evoke the chilling Dark Forest Hypothesis: the idea that the Great Silence is maintained not by loneliness or physical impossibility, but by the ruthless logic of predation, where any civilization that reveals its location risks annihilation by a more powerful neighbor. Whether or not it is safe to broadcast our existence is, in fact, the central and still-unresolved ethical debate at the heart of modern METI research — a debate we will explore in depth in subsequent installments.
Early Experiments: Signaling the Neighbors
The Mathematical Vision of Gauss
The first documented proposal for what we might today call an "active SETI" experiment came not from the Space Age, but from the early 19th century. The great German mathematician and astronomer Carl Friedrich Gauss (1777–1855) — one of the most brilliant minds in the history of science — reportedly proposed around 1820 the creation of an enormous geometric figure on the Earth's surface that would be visible from space. His concept involved clearing a vast region of the Siberian forests and planting them in a pattern representing the Pythagorean theorem — a right triangle flanked by three squares illustrating the relationship a² + b² = c².
The underlying logic was elegant: mathematics, Gauss reasoned, is the one truly universal language, independent of culture, biology, or the particularities of any single world's evolution. Any intelligence capable of observing Earth from the Moon or Mars and recognizing a geometric proof would understand that the creatures below were also intelligent, curious, and capable of abstract reasoning. Whether Gauss ever formally published this proposal remains a matter of some historical debate, but it stands as a remarkable early instance of what we now call interplanetary communication theory.
The Canal Craze and the Dream of Martian Civilizations
The late 19th and early 20th centuries witnessed an explosion of public and scientific enthusiasm for the idea of inhabited neighboring planets — most dramatically, Mars. This mania was substantially ignited by the careful observational work of Italian astronomer Giovanni Virginio Schiaparelli (1835–1910). While conducting systematic observations of Mars during the planet's opposition in 1877, Schiaparelli noted a series of faint, linear features crossing the Martian surface. He described these as "canali" — the Italian word simply meaning "channels" or "grooves," with no particular artificial implication intended.
However, in one of the most consequential mistranslations in the history of science, "canali" was rendered into English as "canals" — a word that unmistakably implies deliberate, artificial construction. The public imagination caught fire. If Mars had canals, it must have builders. If it had builders, it must have a civilization. The implications — and the hopes — were staggering.
No one did more to popularize and elaborate this vision than the American astronomer and businessman Percival Lowell (1855–1916). Heir to a Boston Brahmin fortune and possessed of extraordinary energy and enthusiasm, Lowell constructed a dedicated private Lowell Observatory
