Scientists estimate the nearest intelligent civilization may be 33,000 light-years away. Rare conditions for life make ETIs scarce, but SETI searches remain crucial for discovering whether we are alone in the galaxy.
The search for extraterrestrial intelligence is one of humanity’s most profound quests — but new research suggests the odds of finding a peer civilization in our galaxy may be slimmer than we hope. Scientists now estimate that the nearest advanced civilization could lie roughly 33,000 light-years away.
Why Intelligent Life Is So Rare
Presented at the EPSC-DPS 2025 Joint Meeting in Helsinki, the study by Dr. Manuel Scherf and Professor Helmut Lammer from the Austrian Academy of Sciences in Graz underscores how rare complex life may be. For intelligent life to exist elsewhere in the Milky Way, planets must meet highly specific conditions:
- A nitrogen-oxygen atmosphere with at least 18% oxygen
- Stable carbon dioxide levels to support photosynthesis without triggering a runaway greenhouse effect
- Active plate tectonics to recycle CO₂ and maintain long-term habitability
The researchers highlight that even slight deviations from these conditions drastically reduce the chances for complex, technologically advanced life to emerge.
Timing Matters
The study also considers how long civilizations must endure to overlap with our own. On a planet with 10% CO₂, a civilization would need to persist at least 280,000 years for even one other civilization to coexist with humanity. If multiple civilizations exist simultaneously, their lifespans would need to extend to millions of years. This means that if we do detect an extraterrestrial intelligence (ETI), it is almost certainly far older than humanity.
The 33,000 Light-Year Estimate
Our Sun sits about 27,000 light-years from the galactic center. By modeling biosphere lifetimes, oxygen requirements, and the time needed for technology to evolve, the team estimated the nearest potential technological civilization lies on the far side of the Milky Way, some 33,000 light-years away. These findings suggest that intelligent life is not only rare but likely isolated by vast cosmic distances.
Why the Search Must Continue
Despite the daunting odds, Dr. Scherf emphasizes the importance of continuing SETI efforts. “Although ETIs might be rare, the only way to know is by searching,” he said. A detection would reshape our understanding of life in the universe, while null results would refine models predicting how rare intelligent civilizations truly are.
While these estimates do not account for all variables — including the origins of life, photosynthesis, and multicellular complexity — they provide a sobering perspective on how special Earth might be. Nevertheless, the study reinforces that every signal, every observation, could bring us closer to answering one of humanity’s oldest questions: Are we alone in the galaxy?