Home › Articles › Fermi paradox

The Fermi paradox explained simply: where is everybody?

Billions of stars and planets, and not one signal. Enrico Fermi's question, the proposed answers and the idea of a galaxy that is alive but almost mute.

by L.R. · November 11, 2026 · 6 min read

In brief

In 1950 Enrico Fermi, at lunch with some colleagues at Los Alamos, asked: “But where is everybody?”
The Milky Way has hundreds of billions of stars, and almost all of them have planets. An advanced civilization would have had plenty of time to spread across the galaxy.
And yet, after more than sixty years of searching with radio telescopes, we have not found a single confirmed signal.
Many explanations have been proposed; none has been proven.

A question over lunch

In the summer of 1950, at the Los Alamos laboratory, a group of physicists was talking about flying saucers, which were all the rage in the newspapers at the time. At some point Enrico Fermi, the Italian Nobel Prize-winning physicist, asked something like: “But where is everybody?” The reasoning behind that quip, done quickly in his head as was his habit, was simple and unsettling.

The universe is old and immense. If intelligent life is not a one-off event, some civilization should have arisen millions of years before us. And even traveling slowly, it would have had plenty of time to explore or colonize the galaxy. So why do we see no trace of it?

The numbers behind the paradox

The stars. In our galaxy alone there are estimated to be between 100 and 400 billion. And there are hundreds of billions of observable galaxies.
The planets. Thanks to missions like Kepler, we know that planets are the rule, not the exception. A substantial share of Sun-like stars may have a rocky planet at a distance suitable for liquid water, although estimates vary widely.
The time. The galaxy is more than 10 billion years old. The Earth is 4.5 billion. Many planets are billions of years older than ours.
The speed. It has been calculated that a civilization able to travel at a small fraction of the speed of light, stopping to colonize one system after another, could cross the galaxy in a few tens of millions of years: an instant, on cosmic timescales.

In 1961 the astronomer Frank Drake summed up these factors in a formula, the Drake equation, which estimates how many civilizations capable of communicating should exist in the galaxy. The problem is that almost all of its terms are unknown: depending on the assumptions, the result ranges from a single civilization, our own, to millions.

The great silence

The search for extraterrestrial signals, known as SETI, began in 1960 with Drake himself, who pointed a radio telescope at two nearby stars. Since then, thousands of stars have been listened to. In 1977 a radio telescope in Ohio picked up a signal so unusual that the astronomer who noticed it wrote “Wow!” in the margin. It has never been repeated.

We have to be honest: we have explored only a tiny part of the possible frequencies, directions and moments. The silence is not conclusive proof. But it is a silence that weighs.

The proposed answers

We are alone, or nearly so

According to the Rare Earth hypothesis, popularized in the early 2000s, the conditions for complex life are so particular (a stable star, a large moon, active plate tectonics, a giant like Jupiter acting as a shield) that planets like ours would be extremely rare.

They are there, but we cannot hear them

Perhaps the distances are too great, perhaps civilizations do not last long, perhaps they communicate in ways we do not know how to recognize. Or perhaps they are avoiding us on purpose: this is the “zoo” hypothesis, in which we would be observed without being disturbed.

Something stops them

Finally, there is the idea that somewhere along the road from inert matter to a technological civilization lies an almost insurmountable obstacle. This is the famous Great Filter, to which we devote a separate article.

Where science stops

The Fermi paradox remains open because it rests on a single example: us. We do not know how easy it is for life to arise, nor how easy it is for it to become intelligent. Those are exactly the two numbers that would settle the matter.

From here on we are no longer talking about what science has established, but about a hypothesis: the one proposed in the book Lux Lucis. It should be read as such.

Life is easy, intelligence is hard

Lux Lucis proposes separating the two questions. If life “switches on” almost inevitably wherever there is water, organic chemistry and the light of a stable star, as the book hypothesizes for the early Earth, then simple life should be common in the universe: microorganisms on countless planets.

But the road from simple life to technology is a very long one. The book identifies four difficult steps: from the simple cell to the complex cell, then to organisms with organs and nervous systems, then to intelligence, and finally to technology. On Earth the complex cell appeared only once in about two billion years. If each step succeeded in only a small fraction of cases, civilizations able to build radio telescopes would be few and very far apart, even in a universe full of life.

In this reading, the silence does not contradict widespread life: the galaxy could be alive, yet almost mute.

What remains open

It is an answer that has the merit of being testable, at least in part. If in the coming decades telescopes find gases produced by living organisms in the atmospheres of distant planets, but no artificial signal, that will be a clue in its favor. If instead life turns out to be rare even in its simplest form, everything will have to be rethought.

For now, Fermi's question, asked between one course and the next more than seventy years ago, remains one of the deepest we have ever asked ourselves.

Go deeper in the book

This topic is developed in chapters 1 and 8 of Lux Lucis – Children of the Light.

Read the first chapter for free · English edition in preparation; available now in Italian and Spanish