The Great Silence: The Never-Ending Suspense of the Fermi Paradox

Published in C Magazine

Summer 1950, Lunch at Los Alamos

Countless stars rain down on the desert at night. The wind carries sand, and the dry air irritates the throat. Summer 1950, the cafeteria of the Los Alamos National Laboratory in New Mexico. Physicist Enrico Fermi was sitting at a lunch table with three colleagues: Edward Teller, Emil Konopinski, and Herbert York.

The conversation began with a cartoon that had appeared in The New Yorker magazine at the time. It was a satirical drawing depicting the culprits behind a series of trash can disappearances in New York City as the crew of a flying saucer. The four men laughed as the conversation drifted toward whether faster-than-light travel was possible and how many UFO sighting reports were genuine. According to Teller's recollection, Fermi fell silent for a while in the middle of the conversation, and then asked abruptly, yet quietly.

"Where is everybody?"

"Where is everyone?"

That single remark froze the cafeteria for a moment. The laughter stopped, and only the sound of forks touching plates echoed. According to York's testimony, during that silence, Fermi was mentally estimating the number of stars in the galaxy, the percentage of stars with planets, the probability of life emerging, and the time it would take to reach interstellar travel technology. And he concluded: it would be strange if Earth hadn't been visited many times long ago.

Fermi was legendary for this kind of impromptu estimation. The famous question, "How many piano tuners are there in Chicago?"—the city's population, the percentage of households with pianos, the frequency of tuning, the number of jobs a tuner can handle in a day. Even without any data at hand, he could arrive at an answer with the correct order of magnitude just by multiplying. This method is now called "Fermi estimation." During the Trinity test in July 1945, he dropped small pieces of paper at a point about 16 kilometers from the epicenter and estimated the power of the explosion by visually measuring the distance they were blown by the blast. The order of magnitude matched later precision measurements.

Born in Rome in 1901. After receiving the Nobel Prize in Physics in 1938, he traveled from Stockholm to the United States and never returned to his homeland. On December 2, 1942, in a squash court under the stands of Stagg Field at the University of Chicago, he led "Chicago Pile-1," a stack of graphite blocks and uranium, to criticality, successfully achieving the first controlled nuclear chain reaction in human history. The man whose profession was measuring the shape of the world with numbers had uttered a casual question at lunch. That became the origin of the massive mystery later known as the "Fermi Paradox."

The group present was also symbolic. A few months later, Teller would open the theoretical breakthrough for the hydrogen bomb, and York would later sit at the center of nuclear development as the first director of the Lawrence Livermore National Laboratory. In a desert laboratory where the Cold War had just begun, the very people designing the power to destroy humanity were discussing the absence of intelligence from other stars. This composition itself would become the foreshadowing of a question that would remain for seventy years.

The camera slowly zooms out. It expands from the cafeteria window to the outside, to the desert night sky, and then to the entire galaxy.

The Arithmetic of the Galaxy—The Birth of the Drake Equation

The universe is unimaginably vast. In our Milky Way galaxy alone, there are approximately 200 to 400 billion stars. Of those, it is estimated that there are at least billions to tens of billions of stars located in the "habitable zone" where rocky planets like Earth orbit and liquid water can stably exist. About 13.8 billion years since the Big Bang, and over 10 billion years since the galaxy formed. 4.6 billion years since Earth was born, and about 4 billion years since life began. Enough time has already passed to repeat the journey to intelligent life building a technological civilization many times over.

These numbers, which were once mere speculation, are now being replaced by observation. The Kepler Space Telescope, launched in 2009, detected thousands of planet candidates over four years using the method of capturing the slight dimming when a planet passes in front of its host star. Its successor, TESS, took over, and the number of confirmed exoplanets has exceeded 5,000. The two terms on the left side of the equation—the percentage of stars with planets and the number of habitable planets—are no longer guesses. It has been statistically confirmed that the majority of stars have planets. The denominator continues to swell, and the paradox has only deepened.

It was young radio astronomer Frank Drake who translated this intuition into a mathematical formula. In the spring of 1960, he pointed the 26-meter radio telescope in Green Bank, West Virginia, at Tau Ceti and Epsilon Eridani. For two hundred hours, he listened to 1,420 megahertz, the frequency band emitted by neutral hydrogen—a frequency that any civilization in the universe should know. This was "Project Ozma," the first systematic search for extraterrestrial intelligence in history. The result was silence.

In November 1961, eleven scientists gathered in Green Bank. To organize the agenda, Drake wrote a formula on the blackboard.

N = R* × fp × ne × fl × fi × fc × L

The number of stars born per year in the galaxy, the fraction of those that have planetary systems, the number of habitable planets per planetary system, the probability that life actually emerges there, the probability that it evolves into intelligence, the probability that it reaches a communicative technological civilization, and—finally—the average lifespan of that civilization during which it emits signals. Multiply them together, and you get N, the number of civilizations capable of communication at this very moment.

The conference participants included 27-year-old Carl Sagan, John Lilly, who studied dolphin sounds, and Melvin Calvin, who received news of his Nobel Prize in Chemistry during the conference. Inspired by Lilly's research, they called themselves the "Order of the Dolphin." After three days of discussion, the resulting number for N had a staggering range, from 1,000 to 100 million.

But the range is not what is important. No matter how you multiply the first six terms, the product tends to converge to a value close to 1, and in the end, it is only the final L that determines the magnitude of N. In other words, N ≈ L. Everything depends on the single point of how long a civilization can survive. The equation was less a tool for counting aliens and more a mirror asking about our own remaining time.

The Great Silence—No Radio Signals Return

Fermi's calculation is simple. If there were a spacecraft traveling at 1% of the speed of light, it would take 10 million years to cross the 100,000 light-year diameter of the galaxy. That is only 1/1,000th of the 10 billion years the galaxy has existed. If you compress the life of the galaxy into one year, it is an event that lasts less than nine hours.

In 1980, physicist Frank Tipler introduced an even more severe argument. One only needs to send out a single self-replicating unmanned probe—a machine envisioned by mathematician John von Neumann. It would harvest resources from the asteroid it reaches, create two copies of itself, and each would head to the next star. The number of probes in the n-th generation is,

N(n) = 2ⁿ

In fifty generations, there would be 1.125 quadrillion probes. This far exceeds the total number of stars in the galaxy. There is no need to even consider interstellar travel with ships carrying humans. Yet, not a single machine from another civilization has been found in the solar system. In 1975, astronomer Michael Hart published a paper concluding from this fact that "they do not exist," pushing the paradox formally into the academic agenda.

Meanwhile, efforts on the listening side continued. On August 15, 1977, the "Big Ear" radio telescope at Ohio State University received an unusually strong narrowband signal from the direction of Sagittarius for seventy-two seconds. Jerry Ehman, who checked the printout, circled the character sequence "6EQUJ5" with a red pen and added a single word in the margin—Wow!. For over forty years since, the same signal has never appeared again. SETI@home, which began in 1999, analyzed the sky by borrowing over five million home computers from around the world. Solid evidence remains at zero.

The possibility of missing the signal cannot be ignored either. The intensity of radio waves attenuates in inverse proportion to the square of the distance. If it were routine leakage like television broadcasts, it would dissolve into the cosmic background noise before traveling even a few light-years. What current telescopes can detect is either a powerful beam intentionally aimed at us or the thermal radiation of structures that handle stellar-scale energy. Attempts to search for infrared excesses from giant structures that envelop stars to harvest energy—so-called Dyson spheres, proposed by Freeman Dyson in 1960—are also continuing, but for now, candidates have been explained by natural phenomena.

And the signals we ourselves emit are also unreliable. It has been only a little over a hundred years since humanity began leaking radio waves in earnest. The region reached by those waves is a sphere with a radius of only about 100 light-years, which in terms of volume is only about 1/1.9 millionth of the galactic disk. On the scale of the galaxy, it is less than a blink of an eye. Perhaps their civilizations have already vanished before their signals could reach us. This is the phenomenon known as the "Great Silence."

The Great Filter—Have We Already Passed Through It?

In 1998, economist Robin Hanson provided the coldest hypothesis for this mystery: the "Great Filter." The subtitle of his paper is a question directed at us: "Are we almost past it?"

He divided the path from inanimate matter to interstellar civilization into nine stages: the formation of a suitable star system, the accumulation of organic matter, the emergence of self-replicating molecules, prokaryotic cells, eukaryotic cells, sexual reproduction, multicellular organisms, tool-using intelligence, and expansion to the stars. The total probability is,

P = p₁ × p₂ × … × p₉

Even if the probability of passing each stage were 0.1, the product would be 10 to the power of minus 9. If any one stage were extremely small, it would explain why the galaxy is silent.

There is a basis for thinking there was a filter in the past. Eukaryotic cells were born on Earth about 2 billion years ago; one cell swallowed another and kept it alive without digesting it—this event, which became the origin of mitochondria, has occurred only once in 4 billion years of life history. In 2000, paleontologist Peter Ward and astronomer Donald Brownlee wrote "Rare Earth," listing the coincidences necessary for complex life: Jupiter's gravity acting as a shield against comets, an unusually large moon stabilizing the axis of rotation, and plate tectonics keeping carbon in circulation. We may be the lucky exception that slipped through the filter.

But what if the filter is in the future? The camera shows Earth's cities. Neon lights shine, and silos where missiles sleep stand quietly. On September 26, 1983, at an early warning command post in the suburbs of Moscow, the panel in front of duty officer Stanislav Petrov signaled "launch" five times. If he had reported it to his superiors as per regulations, a chain reaction of retaliation would have begun. He judged it to be a system malfunction and did not report it. It was a false detection caused by sunlight reflecting off high-altitude clouds. Whether the light of civilization would be extinguished depended on one man's judgment that night.

Fermi himself opposed the development of the hydrogen bomb while on the General Advisory Committee. In 1954, he passed away at the age of fifty-three due to stomach cancer. He remained unaware that his question would not receive an answer for half a century.

The Dark Forest, the Zoo, and the Boy on the Rooftop

The reason for the silence is not necessarily absence.

In 1973, astrophysicist John A. Ball proposed the "Zoo Hypothesis." Advanced civilizations already know of us, do not interfere, observe, and protect us. They hide themselves until we reach a stage worthy of being "discovered." The galaxy is not uninhabited; it is a restricted area.

Even colder is the "Dark Forest." In the cosmic view depicted by Chinese science fiction writer Liu Cixin in his 2008 novel "The Dark Forest," every civilization is a hunter walking through a forest. There is no way to verify the goodwill of others, and technology can explode exponentially. Even if an opponent is weak now, they could become a threat in a hundred years. Therefore, the side whose location is known is destroyed first. That is why no one speaks up. Silence becomes the optimal strategy.

This speculation sparked real-world controversy. On November 16, 1974, Drake and Sagan transmitted a 1,679-bit signal from the Arecibo Observatory toward the globular cluster M13. The distance to the target is approximately 25,000 light-years, meaning that even if a reply were sent, it would take 50,000 years to return. Nevertheless, entering the twenty-first century, many scientists and engineers signed a statement opposing 'Active SETI'—the act of proactively transmitting signals—arguing that it was akin to revealing our address to an entity incapable of responding.

Some theorists point to technical limitations. In 1981, Sagan and William Newman countered the premises of Hart and Tipler. Civilizations are not bacteria multiplying exponentially; their expansion is slower, intermittent, and prone to stalling. The galaxy may be quiet simply because they have not arrived yet.

The camera pans over the galaxy once more. Between the swirling stars, the lights of various hypotheses flicker on and off. Yet, none are definitive. Is life truly rare? Is intelligence inevitable? Are we alone in the universe, or are we surrounded by countless neighbors, simply unaware of their presence?

In the climax, the screen returns to modern-day Earth. A boy standing on a rooftop at night photographs the stars with his smartphone. In the distance, the massive dish of a radio telescope rotates slowly. Fermi's question continues to echo above us, even after more than seventy years.

'Where is everybody?'

The stars merely shine in silence. Perhaps that silence is the most eloquent answer in the universe. Or perhaps, in the next moment, something will be heard. The film ends here. Instead of end credits, the night sky simply drifts by. As the audience leaves their seats, they will ask themselves: Are we the only characters on this massive stage? Or are we still only in the prologue?

The Fermi Paradox is as much a philosophical drama questioning the meaning of human existence as it is a scientific problem. It is a never-ending suspense story unfolding on the small stage of Earth against the backdrop of a vast universe. No one knows the answer yet. But every time we look up at the stars, the story waits for its next chapter.