When Will Aliens Contact Us? In About 400,000 Years, Claims Study.

Are aliens ignoring us, or is the universe just so vast that their signals haven't reached us yet?
alien signal contact

Humanity was always curious if intelligent alien life exists beyond Earth. Where are all the aliens if there are so many planets, stars, and galaxies? Why haven’t we heard from them? Questions like these are at the heart of the Fermi Paradox.

In a recent paper, a couple of scientists have tackled the question of “how long will we have to endure before hearing from another alien civilization?” And the answer is 400,000 years.

The paper “the Number of Possible CETIs (communication with extraterrestrial intelligence) within Our Galaxy and the Communication Probability among These CETIs” was published in The Astrophysical Journal. The authors of the paper include He Gao and Wenjie Song, both from the Department of Astronomy at Beijing Normal University.


According to the researchers, “the possibility of being the only advanced sentient civilization is one of the most confusing challenges for humans. A lot of research into extraterrestrial civilization has been conducted in recent decades. Even if studying something we don’t know if it exists is challenging, it doesn’t deter us.”

It’s difficult to study alien civilizations since we only have one data point: people on Earth. Despite this, several academics have approached the subject as if it were a thought experiment, using strict scientific procedures.

How did scientists come up with 400,000 years?

It’s a strong possibility that humanity will not survive 400,000 years. It is a significant amount of time for a species that has only existed for a few hundred thousand years and only discovered farming approximately 12,000 years ago.


The duo of researchers aren’t the first to tackle this question. However, it summarizes prior scientific endeavors to learn more about the occurrence of alien extraterrestrial civilizations in the Milky Way. The figure was derived from calculations incorporating galactic star formation histories, metallicity distributions, and the possibility of Earth-like planets being found in stars’ habitable zones.

Diagram of different habitable zone regions by Chester Harman
Habitable zones of alien planets by Chester Harman under CC BY-SA 4.0

“Until any definitive detection is achieved,” the study says, “the question of extraterrestrial intelligent and communicative civilizations will remain wholly in the area of theory.” They do, however, point out that scientists can still come up with useful models based on logical assumptions “that may at least yield realistic estimates of the incidence rate of such civilizations.”

The latest research on CETIs explained that we’d have to keep this human experiment for 400,000 years if we want to hear from alien civilizations.


How many CETIs exist?

This is a difficult question to answer. “We’ve always wanted to know the answers to the following questions, but we’re not sure how long we’ll have to wait.” To begin, how many CETIs are there in the Milky Way? According to the authors, “we can only learn from a single known data point (ourselves).” But according to one analysis in 2020, there are likely 36 CETIs in the Milky Way.

The Drake Equation comes into play here

Europa Rising Drake Equation
Europa Rising – Drake Equation by Kevin Gill. Licensed under CC BY 2.0

Despite its flaws, as many critics have explained, the Drake Equation tries to estimate how many CETIs there may be in our galaxy. Some of its variables, for instance, are merely guesses. Hence, the number of alien civilizations it calculates is unreliable.

While the Drake Equation is more of a hypothetical scenario than a calculation, the authors of the new paper go a step further to investigate the chances of planets being in the habitable zone and life evolving into a CETI. They used a previously made estimate based on this equation in their analysis. Many factors go into the calculation, including galactic star formation history, metallicity distributions, and the likelihood that the star hosts planets in the habitable zone. They also try to figure out when a CETI would be born in the star’s development.  


Optimistic and pessimistic scenarios.

Song and Gao used different values for these variables in a series of Monte Carlo simulations. They came up with two scenarios: one optimistic and one pessimistic. 

  • The optimistic scenario

A CETI might appear as early as 25% of the star’s lifespan in a best-case scenario. Each planet has a 0.1 percent probability of developing a CETI-like life type. Over 42,000 CETI’s spread out across the galaxy in various phases of evolution in this scenario. In theory, achieving two-way contact with them would only take 2,000 years. That appears to be within grasp.

Spiral galaxy by NASA

But it is the optimistic scenario in which the Universe appears to be friendly and populated by other friendly alien civilizations. Perhaps some of them are already conversing, and we just need to join in. 

  • The pessimistic scenario

In the pessimistic scenario, the sun would have to cool down even more and may have reached its lifespan, with only a 0.001% chance of a CETI forming. This would reduce the number of CETIs in the Milky Way to only 111, with two-way contact with one of them occurring within the next 400,000 years.

That’s twice as long as human civilization has lived on Earth, and climate change, a rogue undetected comet strike, or even nuclear Armageddon may cause enormous changes. It could be possible that human civilization will be long gone before we even make contact with an alien civilization and declare our existence.  

It concerns two parameters, both of which are underappreciated. The first is how many livable terrestrial planets there are and how often life evolves into a CETI on these alien worlds. The second question is when a CETI would be born in the evolution of a host star. In their computations, the researchers made each of these parameters a variable. The chance of life arising and evolving into a CETI is (fc), and the stage of evolution required by the host star is (F).  


Humanity might not live long enough

“But many hypothetical disruptions, such as population concerns, nuclear annihilation, unexpected climate change, rogue comets, ecological changes, and so on, have been offered as reasons for civilizations’ lifespans to be self-limiting. If the Doomsday thesis is right in some gloomy scenarios, humans may not get any signals from other CETIs before extinction.”

“The values of F and fc are full of numerous unknowns,” the researchers write. This is true for all of these types of employment. Like others that address the same issue, this study is best viewed as a series of thought experiments rather than a set of concrete outcomes. 

They explained, “It is quite uncertain what proportion of terrestrial planets can give birth to life, and the process of life evolving into a CETI and being able to send detectable signals to space is highly unpredictable.”


Will humanity ever encounter other alien civilizations? It’s one of our most compelling questions, and it’s almost certain that nobody alive today will ever have an answer. But if humanity needs a goal, something to cling to that can keep hope alive, then communicating with another CETI might do it.