How many aliens in our galaxy? Two researchers’ explanations

ALIENS – Are we alone? The universe is so large that other forms of life are likely to exist. But if so, why have we not heard of them? These are the mysteries at the heart of the Fermi paradox, which call into question the lack of extraterrestrial discoveries.

Published in the magazine The Astrophysical Journal on April 4, a new article is interested in this question and asks the following things: how many possible CETIs are there in our galaxy, and what is the probability of communicating with them successfully?

The two Chinese authors of the study, Wenjie Song and He Gao, members of the Department of Astronomy at Peking University, estimate that there are at least 111 communicating extraterrestrial intelligent civilizations (or CETIs) in our galaxy.

Up to 42,000 intelligent civilizations in our galaxy?

It is difficult to study other civilizations because we have only one point of reference: humans on Earth. Yet many researchers have addressed the problem. A study from 2020, for example, concluded that there are probably 36 CETIs in the Milky Way. The scientific method that had been used has been taken up in this new research, focusing on two parameters that have been hypothetical so far.

The first parameter concerns the number of habitable planets and the frequency with which life on these planets evolves towards an intelligent civilization (CETI). The other is how old its host star is when such a way of life emerges. According to their results, the number of CETIs that exist or have existed in the Milky Way varies from more than 42,000 in the optimistic scenario to 111 in the most pessimistic scenario.

Table of the results of the simulations.  The percentage F at the top represents the stage of development of the host star required for the development of a CETI.  The percentage fc is the percentage of terrestrial planets that can host a CETI.  (Photo: The Astrophysical Journal / Wenjie Song / He Gao / 2022)

Table of simulation results. The percentage F at the top represents the stage of development of the host star required for the development of a CETI. The percentage fc is the percentage of terrestrial planets that can contain a CETI. (Photo: The Astrophysical Journal / Wenjie Song / He Gao / 2022)

Table of simulation results. The percentage F at the top represents the stage of development of the host star required for the development of a CETI. The percentage fc is the percentage of terrestrial planets that can contain a CETI. (Photo: The Astrophysical Journal / Wenjie Song / He Gao / 2022)

For researchers, therefore, in the worst case scenario, there would be more than a hundred life forms to discover within the Milky Way. But to find them, humanity must probably be patient.

To return to their scenarios, the two researchers estimate that it will take at least another 2,000 overrides to establish two-way communication with us. This duration can also be much longer if we follow the pessimistic scenario and push up to 400,000 years.

On the scale of our species, it is very (very) long. In fact, our species has only existed for a few hundred thousand years and only discovered agriculture 12,000 years ago. It is short.

A paradox, hypotheses

The search for other forms of life, many scientists have tackled it. This is the case with Enrico Fermi, one of the creators of the atomic bomb. During a lunch in the 1950s with other physicists, the question of extraterrestrial life came to the table.

The Italian scientist then points this out: given the breadth and age of the universe, if an extraterrestrial civilization existed, it would certainly have had time to spread across thousands of worlds and visit us. So where are they?

This is the “Fermi paradox”. Since then, thousands of people have been trying to find an answer to this problem. In 1961, Franck Drake, an American astronomer, set up an equation to calculate the number of extraterrestrial civilizations in our galaxy. The problem is that this equation has many unknowns. “But we’re beginning to know more of the concepts: the number of stars on planets, the type of planets,” specifies Gabriel Chardin, a physicist at CNRS.

While waiting to solve the “Drake equation”, there are many theories to explain the Fermi paradox. Some not very serious, others are based on real scientific foundations.

The big filter problem

At this point, the big filter comes into play. Defined in 1998 by Robin Hanson, it is a series of barriers that prevent the emergence of an advanced extraterrestrial civilization. The authors approach this problem as follows: “The lifespan of civilizations is most likely self-limiting due to many potential disruptions, such as population problems, nuclear annihilation, sudden climate change, comet rebellions, ecological change, etc.”

But will humanity ever meet another civilization? As with all questions regarding this topic, the mystery remains as there are so many unknowns. Therefore, it is not impossible to imagine a scenario where “people may not receive any signals from other CETIs before their extinction.”

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This article originally appeared on The HuffPost and has been updated.

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