How rare are galactic neighbours? Study explores lifespan & distance of alien civilizations

The nearest technological civilisation inside our Milky Way galaxy could be around 33,000 light-years away, but it would need to survive for at least 280,000 years to coexist with humanity.

This finding was recently presented by Austrian researchers Manuel Scherf and Helmut Lammer at a conference in Helsinki, as reported by Europlanet.

A central factor in their calculations was the conditions required for complex life to emerge and remain stable. A planet must have plate tectonics, which regulate atmospheric carbon dioxide, and an atmosphere rich in oxygen and nitrogen. Without these conditions, the biosphere would eventually degrade, preventing the development of a technological civilization.

The researchers determined that an atmosphere containing roughly 10% carbon dioxide could sustain a biosphere for up to 4.2 billion years. However, at least 18% oxygen is required for a technological civilization: “without it, neither large animals nor open fire—essential for metallurgy—could exist.”

By comparing the lifespan of the biosphere with the rate of evolution on Earth, the scientists concluded that for even one civilization to exist simultaneously with ours, its species would need to survive at least 280,000 years. To have ten civilizations coexisting at the same time, the average lifespan of each would need to exceed 10 million years.

Scherf notes that other factors should also be considered, including the origin of life, the emergence of photosynthesis, the development of multi-cellular life, and the frequency with which intelligent life evolves technology. “If each of these factors has a high probability, then extraterrestrial life (ETI) might not be as rare. If each of these factors has a low probability, then a more pessimistic outlook is required.”

“Although ETIs might be rare there is only one way to really find out and that is by searching for it,” Scherf says. “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.”