Humans have spent centuries wondering if there is other intelligent life among us in the galaxy and decades actively searching for it. It turns out the Milky Way may have once been full of bustling alien civilizations, but they are all dead now. That is the depressing finding of a new study published in the arXiv database last month.
The paper, which is a preprint and awaiting peer review, amounts to an update to the Drake equation, a probabilistic model used to estimate the number of extraterrestrial civilizations in the Milky Way galaxy developed in 1961 by astronomer and astrophysicist Frank Drank. Using modern astronomy and statistical modeling techniques, a team of physicists from the California Institute of Technology were able to identify different factors that would point to the potential existence of extraterrestrial life. Using research conducted in recent years, driven largely by discoveries made possible thanks to the Hubble Space Telescope and Kepler Space telescope, the scientists were able to examine conditions within the galaxy that could result in alien civilizations. That includes factors like sunlike stars near Earthlike planets, frequency of supernovas, and the time necessary for intelligent life to develop under the right conditions. Perhaps most importantly, they took into consideration the tendency of advanced civilizations to experience self-annihilation. And as it turns out, any alien life that came before us likely gave into that tendency long before we showed up on the scene.
Researchers found that the probability for intelligent life hit its highest point about 8 billion years after the Milky Way was formed, and about 13,000 light-years from the center of the galaxy. The Earth occupies a space that is about 25,000 light-years from that central point and didn't crop up until about 13.5 billion years after the Milky Way formed. That means humans came along pretty late in the game, missing out on that peak point for intelligent civilization. It also means that there may be other life behind us that is just getting started.
That leaves open the potential for discovering intelligent life at some point, just not life that came before us. The research suggests that those civilizations that may have gained their smarts billions of years before we were even a twinkle in the eye of the universe probably destroyed themselves long ago. The model suggests that over time, the probability for intelligent life to completely eradicate itself increases the longer it’s around.
It's hard to say what exactly doomed those civilizations, but one doesn't have to look too far from our own circumstances to imagine what may have affected those that came before us. As we stare down the barrel of climate change and are plagued by international inaction from political and industrial leaders, it's easy to imagine how previous beings managed to self-destruct due to the same kind of hubris that might doom humanity. Intelligent life might be a generous description, after all.