Even though we still don’t have a firm grasp of how solar systems form, there are those ready to jump out and try and define how often life must form. We anticipate the next press release we’re going to discuss is going to lead to a lot of click-bait headlines, and we’re bringing it up so we can critically discuss what this story means. 

In a new paper in the Astrophysical Journal, researchers led by Christopher Conselice describe their latest calculations of how many potentially communicating, technologically advanced civilizations may exist in our universe. According to the press release, the number is thirty-six, which strikes us as a bit overly precise. To be fair, the actual paper offers error bars, saying there should be 36 +175 or -32 civilizations. They also give a sound mathematical description of where this estimate comes from. This team used what I would describe as a simplified version of of the famous Drake equation, and asks “how many worlds have had the needed five billion years, or more broadly 4.5-5 billion years to evolve life?” and then assumes each of these civilizations will be detectable from their communications for a hundred years. 

This simple “has it been around long enough, and is it likely in that 100-year window” calculation considers how many stars have planets and how long those stars have been around and essentially assumes that if a world forms, it will evolve life. This is a somewhat large assumption, and really, I personally like the Drake equation’s more nuanced approach that considers how likely it is for a society to kill itself off and other more complicated ideas, but if life does find a way and it typically takes 4.5 to 5 billion years, we now know how many planets could be out their spewing radio signals into space. Unfortunately, given the volume of the galaxy, they are likely no closer than 17,000 light-years away, and we will never hear them. If a civilization exists out of earshot, does it still make a signal?

More Information

The University of Nottingham press release 

 “The Astrobiological Copernican Weak and Strong Limits for Extraterrestrial Intelligent Life,” Tom Westby & Christopher J. Conselice, 2020 June 15, Astrophysical Journal (Preprint on arxiv.org)