This Monday, the Astrophysical Journal featured a new approximation of the number of radio-capable civilisations we might be sharing our galaxy with. The conservative estimate is 36, based on a new solution to the Drake Equation. “The Drake Equation is our best and only tool for trying to tackle this age-old question, even though it’s based on things that are still wildly speculative,” said Tom Westby, an engineer at the University of Nottingham in the UK and co-author of the research, along with astrophysicist Christopher Conselice.
The Drake Equation, written in 1961 by Frank Drake, is used to estimate the number of communicative extraterrestrial civilisations in our galaxy. It includes 7 different variables and is intended to provoke scientific discourse around the means of calculation of the values of these variables, more so than the final answer itself.
Westby and Conselice took a philosophical approach towards certain variables we have little to no information for, such as f1 (the fraction of planets that could support life that actually develops life at some point), fi (the fraction of planets with life that actually go on to develop intelligent life (civilizations)) and L (the length of time for which such civilizations release detectable signals into space). They assumed that the human race was no different than any other potentially intelligent species, and technologically capable life would take the same time to evolve on any Earth-like planet as it did here (around 5 billion years). They also assumed that such a civilisation would survive for at least a 100 years after inventing radio transmitters, just like humans.
These assumptions are based on a principle known as the ‘Mediocrity Principle’, the idea that there is nothing intrinsically different about the species that would put us at an advantage or a disadvantage when it comes to evolving and building a technologically capable civilisation.
The researchers have come under fire for their use of the Mediocrity Principle, primarily by other scientists who express concerns about our lack of knowledge as to whether humanity is the rule or the exception to it. However, according to Westby, “That’s the great problem with astrobiology, trying to extrapolate from one data point here on Earth. But if we are one of a sample, we should expect ourselves to be typical in most respects.”
36 civilisations in a galaxy having billions of stars might seem low. But Westby notes that the Milky Way hit its star-formation peak around 10 billion years ago and that other radio-capable civilisation might have been active around 5 billion years ago. This was the time when Earth had just started to harbour microbial evolution. If these civilisations were jetting about the galaxy back then, there might be some merit to the Panspermia hypothesis; that life might not have originated on Earth, but been brought here by some extraterrestrial activity.