For decades, humanity has been staring at the stars. However, new research suggests that the truth may be more calm than the dreams of science fiction.
If intelligent beings exist elsewhere in the Milky Way, they can be unimaginably rare, unimaginably old, and unimaginably far apart.
New research presented at the EPSC-DPS 2025 joint conference in Helsinki suggests that if technological civilizations exist in our galaxy, they are very rare and likely to be much older than humanity.
The research shows that the closest civilization with advanced technology is likely to be around 33,000 light years away, potentially located across the Milky Way.
The delicate balance of addictiveness
A research team led by Dr. Manuel Schöff and Professor Helmut Rammer of the Austrian Academy of Sciences have investigated the exact conditions required for long-term planetary habitability.
Planets that support alien life require not only liquid water but also finely tuned atmospheres rich in nitrogen and oxygen, which are alleviated with plate tectonics.
Carbon dioxide plays a crucial role. Too many, out-of-control greenhouse effects can wipe out livability. On Earth, plate tectonics regulate this balance by cycling carbon between the atmosphere and rock.
However, this process also has limitations. Scientists estimate that in 200 million to 1 billion years, carbon dioxide in the atmosphere will be trapped in rocks, too little to sustain plant life, and Earth’s photosynthesis could collapse.
Why oxygen is essential to technology
Carbon dioxide helps maintain the biosphere, while oxygen determines whether civilization can advance technologically.
Researchers calculated that at least 18% oxygen is required to support both large and complex organisms and the potential for fire. Without fire, there is no metal smelting. Therefore, there is no way to industrial or technological development.
This threshold places additional barriers to search for alien life. Even if microbial organisms are common throughout the galaxy, intellectual life where technology can be constructed may be extremely rare.
Civilization needs to last for hundreds of thousands of years
One of the most impressive findings relates to the lifespan of technological civilizations.
On Earth, it took 4.5 billion years for humans to evolve, but researchers estimate that in order for us to share galaxies even with one other advanced civilization, the species must endure at least 280,000 years since becoming a technology.
The odds for multiple civilizations are steeper. To have ten highly advanced societies that exist simultaneously, each of them must have an average lifespan of more than 10 million years.
If these numbers apply, the alien civilizations we may encounter in the end will almost certainly be much older and potentially much more advanced.
What does this mean for SETI?
The findings raised questions about SETI’s potential for success (search for extraterrestrial intelligence). However, researchers emphasize that search remains essential.
An unknown factor that could dramatically change odds, such as how often life occurs, how often complexity develops, and how quickly intelligence occurs.
If these factors tilt towards a higher probability, alien life may not be more unusual than this model suggests. If they tilt lower, we may certainly be alone, at least in our galaxy neighborhood.
Scherf explained:
“If we can’t find anything in these searches, it makes our theory more possible, and if Seti finds something, it will be one of the biggest scientific breakthroughs ever achieved, as we know we’re not alone in the universe.”
Whether Seti confirms our loneliness or reveals distant civilizations, the outcome will shape human understanding of that place in the universe.
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