The Fermi paradox states that if humans are not special and civilizations can arise regularly in the universe, why haven’t we found anyone else yet? (There have been some pretty bold solutions in the past, and yes, sorry, any Star Trek-like scenario is out.)
Remembering Carl Sagan
A few weeks ago, a team of scientists announced their plans to transmit a message, in the style of the golden discs that contain the Voyager probes (the Sounds of the Earth ) – whose content was selected for NASA by a committee chaired by Carl Sagan – and which were launched in 1977. This updated radio message contains the location of the Earth in deep space, with the hope that one day it can be received and understood by an alien civilization.
Now another team of scientists has made an estimate of how long it might actually take us to contact aliens . They estimated the number of communicating extraterrestrial intelligent (CETI) civilizations that exist using two parameters: the probability of life appearing on a terrestrial planet and the stage of evolution of the planet’s host star in which this civilization would be born.
Song and Gao ran a series of modeling scenarios using different values for these variables and obtained an optimistic and a pessimistic outlook.
They came up with two possible scenarios by looking at the extremes: at best, it could be around two millennia (yes, ‘only’ 2,000 years), experts at Beijing Normal University in Beijing, China estimate, while in pessimistic view the wait would be much longer: 400,000 years to be precise.
The optimist used the values F = 25 percent and fc = 0.1 percent, meaning that a star must be at least 25 percent alive before a CETI can emerge and for each terrestrial planet, there are only a 0.1 percent chance of a CETI appearing. The pessimistic scenario variables were F = 75 percent and fc = 0.001 percent.
They would need to survive for thousands of years
“As the only advanced intelligent civilization on Earth, one of the most perplexing questions for humans is whether our existence is unique. The reason why we have not received a signal may be that the communication lifetime of humans is not long enough at present”, explain authors Wenjie Song and He Gao in their study published in The Astrophysical Journal.
Specifically, they managed to generate nine scenarios in which these extraterrestrial intelligent civilizations were rare or common. If CETIs are rare (on the order of 110 in the entire Milky Way ), then this civilization might have to survive for 400,000 years before receiving a signal from another. At best, with around 43,000 CETI, it would take at least 2,000 years for a communicating civilization to get its first cosmic wave.
Skeptical?
You are not the only one. It is currently impossible for us to know scientifically how many civilizations there are out there, if any . However, studies like this allow us to produce valuable models based on logical assumptions “that can at least produce plausible estimates of the rate of occurrence of such civilizations.”
“The reason we haven’t received a signal may be that the communication lifespan of humans is not long enough at present. However, it has been proposed that the lifespan of civilizations is very likely to be self-limiting (known as the doomsday argument), due to many potential disturbances, such as population problems, nuclear annihilation, sudden climate change, rogue comets , ecological changes, etc… If the Doomsday argument is correct, in some pessimistic situations, humans may not receive any signal from other CETIs before extinction ,” the researchers conclude.
Referencia: Wenjie Song and He Gao. The Number of Possible CETIs within Our Galaxy and the Communication Probability among These CETIs. The Astrophysical Journal. Published 2022 April 4 • 2022 The Astrophysical Journal, Volume 928, Number 2 DOI: 10.3847/1538-4357/ac561d
