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A study from June 2020 by the University of Nottingham, led by astrophysicist Christopher Conselice, suggested that there could be up to 36 intelligent alien civilizations in the Milky Way with communication potential, using a model called the Strong Copernican Astrobiological Limit.
The hypothesis is based on a hard premise: if conditions similar to those on Earth are repeated on other worlds, then intelligent life could arise and last long enough to attempt to communicate. The problem arises when this life is spread across an ancient, gigantic galaxy that’s too slow for human-scale conversations.
The discussion gains weight because it’s not just imagination about ETs. The calculation was made based on clear variables and constraints, and the result falls exactly on the most uncomfortable point of the debate: whether there are alien civilizations, why is there no answer, noise, trace, or evident contact?
What The Study Claims And Who Signs The Estimate
The survey was attributed to scientists at the University of Nottingham, led by astrophysics professor Christopher Conselice, and was published in June 2020.
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The headline number, 36, is not presented as absolute certainty, but rather as an estimate based on a scenario considered “strong” within the model itself.
The proposal is that there are civilizations capable of emitting detectable signals, meaning not just microbial life, but technological societies that could theoretically produce communication on an interstellar scale.
How The Drake Equation Was Simplified And What Factors Were Included In The Calculation
Instead of using the entire Drake Equation, the researchers simplified the problem and focused on three main blocks:
Star Formation Rate
The idea is that the number of stars generated over time defines the size of the “board” where planetary systems appear.
Proportion Of Stars With Planets In Habitable Zones
This is where the more direct cut enters: stars that have planets in regions where temperature could allow Earth-like conditions.
Probability Of Intelligent Life Developing
This is the most sensitive point, as it requires assuming not only life, but intelligent life, with enough duration to exist at the same time as another civilization and have a chance to signal.
The model explicitly assumes that the conditions that allowed evolution on Earth can be replicated on other planets in the Milky Way, creating the possibility of technological societies.
The Strong Copernican Astrobiological Limit And The Bet On “Earth-Like Worlds”
The study was described as based on the Strong Copernican Astrobiological Limit, a framework that treats Earth as a not too special example, meaning not as an absolute exception, but as a case that could repeat itself where conditions are similar.
The reasoning is that if planet Earth is not a statistically impossible accident, then there will be other places with a similar combination of factors.
This assumption is the engine that drives the estimation of alien civilizations with communication potential.
The Scale Of The Milky Way Makes The Search Almost Impractical
The Milky Way is presented as having 10 billion years, with over 100 billion stars. This dimension creates two simultaneous problems:
Location
Even if there are 36 alien civilizations, they may be distributed across a vast structure, making any complete and quick scan difficult.
Time
In astronomy, distance becomes a delay. A signal emitted today may take centuries or millennia to reach a distant detector, depending on the point in the galaxy.
This is the kind of detail that changes the tone of the debate: it’s not just “is there life or not,” it’s “even if there is, can it be perceived?”
The Average Distance Of 17 Thousand Light-Years And Why Talking Would Be A Nightmare
The data that makes everything colder is the suggested average distance: about 17 thousand light-years between these possible civilizations and Earth.
In practice, this places communication on a scale incompatible with any human expectation.
If a signal traveled at the speed of light, it would still take thousands of years to cross that space.
And if there were a response, the return would take thousands more years.
A conversation becomes a millennium-long interval, and the chance of two technologically active civilizations existing at the same time becomes another bottleneck.
The Fermi Paradox And The Silence That Disturbs More Than The Number 36
The Fermi Paradox arises exactly from this shock: if the universe and galaxy have ample space and time for life to arise, why don’t we see evidence?
The study enters this discussion as fuel, because it suggests a non-negligible quantity of alien civilizations, but the sky remains silent regarding unequivocal signals.
The paradox is not proof of absence, but rather a logical problem: expectation versus observation.
The Hypotheses Cited To Explain The Silence: Great Filter And Self-Destruction
Two explanations appear as attempts to close the gap:
Great Filter
The idea of a barrier in the path of developing intelligent life. This filter could be at any stage, from the emergence of life to the technological capacity to emit detectable signals.
Self-Destruction Before Interstellar Communication
Even if alien civilizations arise, they might collapse before mastering the technology and social stability to sustain interstellar communication for long enough.
These hypotheses are uncomfortable because they shift the question back to Earth: if the filter exists, has humanity already passed it or will it still face this barrier?
What The SETI Represents Within This Scenario
In the presented scenario, initiatives like SETI come in as a continuous effort to detect signs of intelligent life.
The central point is that, even with gigantic distances, observing and searching still makes sense, because a single consistent signal would change the entire debate.
At the same time, the absence of clear detection so far fuels the paradox itself and reinforces the weight of “silence” as part of the mystery.
Do you believe that silence exists because alien civilizations are too far away, or because almost all disappear before managing to communicate?
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