Does life exist elsewhere in the universe? Are there other civilizations out there asking themselves the same question? So far, we don't have a strong answer for either.
A new paper, published in the Proceedings of the National Academy of Sciences, provides a statistical analysis of how likely intelligent life is beyond our planet. The analysis uses a technique called Bayesian Inference that allows for updating the probability of a hypothesis when more data becomes available.
Many discussions start by using life on Earth as a measure for the likelihood of life elsewhere, but there are doubts as to whether our planet is a good example. Life emerged on Earth during the first fifth of the planet’s existence and yet intelligent life only developed a cosmic heartbeat ago. This research starts in the same way but asks if we were to rerun the emergence of life on Earth, would it play out in the same way?
“The rapid emergence of life and the late evolution of humanity, in the context of the timeline of evolution, are certainly suggestive,” lead author Professor David Kipping, from Columbia University, said in a statement. “But in this study it’s possible to actually quantify what the facts tell us.”
Kipping had four possibilities: Life is common and so is intelligence. Life is common but intelligence is rare. Life is rare but when it happens intelligence is common, and finally, life is rare and intelligence is too. We can’t have complete certainty for any of these, but thanks to Bayesian Inference we can achieve something like betting odds.
On an Earth rerun, life will most likely emerge again at a 9:1 odds. And while elsewhere in the universe conditions might be slightly different, the early emergence of life suggest that our planet is far from a one-of-a-kind location. The question of intelligence is more complex.
We only have a vague idea of how life emerged, and the emergence of intelligence is even less clear. Having only us as an example, with no evidence of other intelligent species beyond Earth, Kipping gets a 3:2 odds that intelligence is rare. But given that the odds are close to a coin toss, it’s a mere nudge towards a hypothesis rather than a robust result.
“If we played Earth’s history again, the emergence of intelligence is actually somewhat unlikely. The analysis can’t provide certainties or guarantees, only statistical probabilities based on what happened here on Earth,” Kipping said. “Yet encouragingly, the case for a universe teeming with life emerges as the favored bet. The search for intelligent life in worlds beyond Earth should be by no means discouraged.”