The Fermi paradox

The Fermi paradox is the puzzle of why we see no evidence of alien civilizations even though the galaxy has billions of planets and billions of years in which life could have spread. It is named for Enrico Fermi, who asked “where is everybody?” in 1950. As of October 2026 there is still no confirmed sign of life beyond Earth, let alone intelligence.

The paradox sits at the center of the question “are we alone?”, which our astrobiology guide covers from the evidence side: Mars, the icy moons and exoplanet atmospheres.

Where the question came from

In the summer of 1950, over lunch at Los Alamos, Fermi and colleagues including Edward Teller, Emil Konopinski and Herbert York were joking about a spate of flying saucer reports. Fermi suddenly asked, in words usually remembered as “where is everybody?” His point, as attendees later recalled it, was that if technological civilizations are common and long-lived, some should have reached us by now.

Fermi never wrote it up. The argument was made rigorous in 1975 by astrophysicist Michael Hart, who argued that the absence of extraterrestrials on Earth is itself a fact needing explanation, and that the simplest explanation is that there are none in our galaxy.

The argument in four steps

1. Planets are common. More than 6,000 exoplanets are confirmed, and surveys suggest most stars have planets, many of them rocky and some in habitable zones (exoplanets guide).
2. There has been plenty of time. The Milky Way is about 13 billion years old. Earth formed about 4.6 billion years ago, so many planets are billions of years older than ours.
3. Spreading is fast on cosmic timescales. Even at a few percent of light speed, a civilization could settle the galaxy in a few million to tens of millions of years.
4. Yet we see nothing. No probes, no artifacts, no confirmed radio or laser signals, no engineered starlight.

The paradox is the clash between steps 1 to 3 and step 4.

The main proposed solutions

Proposed answers fall into three families: life is rare, civilizations are short-lived or quiet, or they are out there and we are not seeing them.

Family	Example idea	What it predicts	Can we test it?
Life is rare	Rare Earth (Ward and Brownlee, 2000)	Simple life may be common, complex life very rare	Partly: search for simple life on Mars, Europa, exoplanets
A hard step is rare	The Great Filter (Robin Hanson, late 1990s)	Some step, such as the origin of life or of complex cells, almost never happens	Partly: finding independent life nearby would move the filter
Civilizations do not last	Self-destruction or collapse	Few civilizations exist at any one time	Indirectly, via the Drake equation’s lifetime term
They stay home or stay quiet	Expansion is costly, or they choose silence	Little interstellar travel or broadcasting	Hard, but deep technosignature searches can constrain it
They avoid us	The zoo hypothesis (John Ball, 1973)	Silence, by design	Essentially untestable
We have not looked enough	The search is still tiny	Signals exist below our limits	Yes: SETI sensitivity keeps improving

“We have barely looked”

The most mundane answer may be the strongest. Radio searches began only in 1960, when Frank Drake pointed a telescope at two nearby stars in Project Ozma, following the 1959 proposal by Giuseppe Cocconi and Philip Morrison to listen near the 21-centimeter hydrogen line (Cocconi and Morrison 1959). Since then searches have covered only a minute fraction of the possible combinations of sky position, frequency, time and signal type. Breakthrough Listen, launched in 2015, is the largest such program so far.

“Life itself is rare”

We still have exactly one example of life, so we cannot measure how often it starts. Chemistry suggests the ingredients are easy: the 1953 Miller-Urey experiment made amino acids from simple gases and sparks (Miller 1953). But making ingredients is not the same as making a cell. A single discovery of independent life on Mars or Enceladus would show that life starts easily, and would push any Great Filter uncomfortably into our future.

The Drake equation: putting numbers on the silence

In 1961 Frank Drake wrote an equation for a meeting at Green Bank, West Virginia, to organize the question. The number of detectable civilizations in the galaxy equals the product of:

1. the rate of star formation in the galaxy,
2. the fraction of stars with planets,
3. the number of habitable planets per system,
4. the fraction of those where life arises,
5. the fraction where intelligence evolves,
6. the fraction that develop detectable technology,
7. the length of time they remain detectable.

The first three terms are now measured or estimated from data. The last four are guesses spanning many orders of magnitude, which is why estimates range from “we are alone” to “millions of civilizations.” A 2018 analysis by Anders Sandberg, Eric Drexler and Toby Ord argued that once those uncertainties are taken seriously, there is a substantial probability that we are alone in the observable universe, so the silence need not be surprising.

What would change the picture

The paradox is not just philosophy. Specific observations would shift it:

• A second origin of life in the solar system. Perseverance’s “Cheyava Falls” rock holds a potential biosignature that only sample return could test (Hurowitz et al. 2025).
• Biosignature gases on exoplanets. The disputed K2-18b claim shows how hard this is (K2-18b).
• Technosignatures. Radio, laser or infrared signs of technology. In 2026 a Very Large Array and MeerKAT search of K2-18b for technosignatures found nothing.
• Interstellar visitors. Three interstellar objects have passed through the solar system since 2017, all natural. The most recent, comet 3I/ATLAS, prompted speculation it might be artificial; the observations show an ordinary, if ancient, comet.

Our take

The honest answer in 2026 is that we do not know whether the galaxy is empty, quiet or simply unsearched. What has changed is that parts of the question are becoming measurable: we now know planets are common, and telescopes like the James Webb Space Telescope and the coming Extremely Large Telescope can start testing the “life is rare” branch directly.

For a short animated overview, our video library includes Kurzgesagt’s “The Fermi Paradox: Where Are All The Aliens?”

Sources

1. Jones, E. M. (1985). “Where is everybody?” An account of Fermi’s question. Los Alamos National Laboratory report LA-10311-MS. [history]
2. Hart, M. H. (1975). An Explanation for the Absence of Extraterrestrials on Earth. Quarterly Journal of the Royal Astronomical Society 16, 128. [primary]
3. Cocconi, G. and Morrison, P. (1959). Searching for Interstellar Communications. Nature 184, 844. https://doi.org/10.1038/184844a0 [primary]
4. Sandberg, A., Drexler, E. and Ord, T. (2018). Dissolving the Fermi Paradox. https://arxiv.org/abs/1806.02404 [preprint]
5. Ball, J. A. (1973). The zoo hypothesis. Icarus 19, 347. [primary]