For decades, humanity has gazed at the stars, wondering if alien life is out there. But new research suggests the truth may be more sobering than science fiction dreams.
If intelligent beings exist elsewhere in the Milky Way, they are likely unimaginably rare, unimaginably old, and unimaginably far away.
New research presented at the EPSC–DPS 2025 Joint Meeting in Helsinki suggests that if technological civilisations exist in our galaxy, they are likely to be both incredibly rare and vastly older than humanity.
According to the study, the closest civilisation capable of advanced technology could be around 33,000 light-years away, potentially situated on the far side of the Milky Way.
The delicate balance of habitability
The research team, led by Dr Manuel Scherf and Professor Helmut Lammer from the Austrian Academy of Sciences, explored the precise conditions required for long-term planetary habitability.
A planet that supports alien life needs not only liquid water but also a finely tuned atmosphere rich in nitrogen and oxygen, moderated by plate tectonics.
Carbon dioxide plays a pivotal role: too little, and photosynthesis fails; too much, and a runaway greenhouse effect can wipe out habitability. On Earth, plate tectonics regulate this balance by cycling carbon between the atmosphere and rocks.
However, even this process has limits. Scientists estimate that in 200 million to one billion years, Earth’s own photosynthesis may collapse as atmospheric carbon dioxide becomes locked away in rocks, leaving too little to sustain plant life.
Why oxygen is essential for technology
While carbon dioxide helps maintain a biosphere, oxygen determines whether a civilisation can advance technologically.
The researchers calculated that at least 18% oxygen is required to support both large, complex organisms and the possibility of fire. Without fire, there would be no smelting of metals – and thus no path to industrial or technological development.
This threshold places an additional barrier in the search for alien life. Even if microbial organisms are common across the galaxy, intelligent life capable of building technology may be exceptionally rare.
Civilisations must last hundreds of thousands of years
One of the most striking findings relates to the lifespan of technological civilisations.
On Earth, it took 4.5 billion years for humans to evolve, but researchers estimate that for us to share the galaxy with even one other advanced civilisation, that species would need to endure at least 280,000 years after becoming technological.
The odds become steeper for multiple civilisations: to have just ten advanced societies existing simultaneously, the average lifespan of each would need to exceed 10 million years.
If these numbers hold true, any alien civilisation we might eventually encounter would almost certainly be far older, and potentially far more advanced, than our own.
What this means for SETI
The findings cast doubt on the likelihood of success for SETI (the Search for Extraterrestrial Intelligence). Yet the researchers stress that the search remains vital.
Unknown factors, such as how often life originates, how frequently it develops complexity, and how quickly intelligence arises, could change the probabilities dramatically.
If those factors lean toward higher probabilities, then alien life might be less rare than this model suggests. If they lean lower, we may indeed be alone, at least in our galactic neighbourhood.
Scherf explained: “Although extraterrestrial intelligences might be rare, there is only one way to really find out, and that is by searching for them.
“If these searches find nothing, it makes our theory more likely, and if SETI does find something, then it will be one of the biggest scientific breakthroughs ever achieved, as we would know that we are not alone in the Universe.”
Whether SETI confirms our solitude or reveals a distant civilisation, the outcome will shape humanity’s understanding of its place in the cosmos.
