Are we alone? Intelligent aliens may be rare

A new study reexamines the Drake equation, a famous formula used to estimate the number of technologically advanced civilizations in our galaxy, using probabilistic logic. The research, led by astronomers David Kipping and Geraint Lewis, explores the idea that the universe should either be teeming with life or almost entirely devoid of it. This conclusion is based on a probability distribution first introduced by J. B. S. Haldane in 1932. The study suggests that if life can emerge on one Earth-like planet, it should theoretically emerge on all similar planets, leading to two extreme outcomes: either life is everywhere or it's incredibly rare.

Kipping and Lewis applied this probabilistic logic to the Drake equation, which was originally developed by Frank Drake in 1961 to estimate the number of technological civilizations in the Milky Way. They simplified the equation by focusing on two main factors: the birth and death rates of extraterrestrial technological instantiations (ETIs). This approach sidesteps the need for precise knowledge of several unknown variables in the original equation, such as the fraction of planets that develop intelligent life. Instead, it uses a more general method to predict the number of ETIs in the galaxy.

One of the study's key insights is that if intelligent alien civilizations existed and were capable of spreading across the galaxy, we would likely have detected their presence by now through their signals or megastructures. Since we haven't, the researchers suggest that either technological life is exceedingly rare, or we are in a part of the universe that hasn't been colonized yet. This could mean that while the universe might be crowded with life in certain regions, our solar system could simply be isolated.

The study also considers the possibility that interstellar travel and megastructure-building are too difficult or undesirable for advanced civilizations. It’s possible that many ETIs prefer a more sustainable existence without the need for colonization. The researchers also note that the search for extraterrestrial signals has been limited so far, meaning we could have easily missed signs of alien life.

Kipping and Lewis encourage continued efforts in the search for extraterrestrial intelligence (SETI), including expanding the search to other galaxies. They argue that despite the lack of evidence, the probability of a crowded universe is still worth considering. The study is currently available as a pre-print and has been submitted for peer review. You can learn more about this intriguing research on Space.com.