spaceSpace and PhysicsspaceAstronomy

It May Take 400,000 Years To Connect With Alien Civilizations, Scientists Say

Where is everyone?


Dr. Alfredo Carpineti


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

Alfredo (he/him) has a PhD in Astrophysics on galaxy evolution and a Master's in Quantum Fields and Fundamental Forces.

Senior Staff Writer & Space Correspondent

Radio telescope looking towards the heavens.

Where could everyone be?

Image Credit: sdecoret/

The Fermi Paradox puts forward the following puzzling question, if humans are not special and civilizations can rise commonly in the cosmos, why are we yet to find anybody else? 

A science paper has a bold answer. Even if there are tens of thousands of civilizations out there, they need to survive for thousands of years to have a chance to talk to someone else.


There have been some concerning solutions to the Fermi Paradox so just having to wait doesn't seem too bad. 

As reported in The Astrophysical Journal, researchers Wenjie Song and He Gao estimated the number of communicating extraterrestrial intelligent civilizations (CETIs) out there using two parameters: the probability of life appearing on a terrestrial planet and the stage of the planet’s host star's evolution at which the CETI would be born. 

The two researchers created nine scenarios where CETIs were either rare or common. If CETIs are rare (in the order of 110 across the whole Milky Way) then a communicating civilization might have to survive for 400,000 years before it gets a signal from another. In their best-case scenario, with around 43,000 CETIs, it would take at least 2,000 years for a communicating civilization to get its first cosmic hello. 

“The reason why we have not received a signal may be that the communication lifetime of human is not long enough at present. However, it has been proposed that the lifetime of civilizations is very likely self-limiting (known as the Doomsday argument), due to many potential disruptions, such as population issues, nuclear annihilation, sudden climate change, rogue comets, ecological changes, etc,” the authors, from Beijing Normal University, wrote in the paper. “If the Doomsday argument is correct, for some pessimistic situations, humans may not receive any signals from other CETIs before extinction.”


Probabilistic approaches to the Fermi Paradox have been brought forward in the last few years, suggesting that our current search for other civilizations is still very much limited and it might stay that way. After all, if someone was looking for us they would have to be within a very small region of the galaxy to actually spot some Earth signals. That said, the teams admit that there are huge uncertainties in their probabilities, so maybe there is a chance out there to communicate with aliens sooner rather than later.  

“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,” the authors explain.

But big uncertainty also works the other way, that there may just be very few CETIs out there. And who knows if they want to talk to us. Maybe the dark forests hypothesis is true after all.

An earlier version of this article was published in May 2022.


spaceSpace and PhysicsspaceAstronomy
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