A team of scientists has calculated the most-likely number of contactable alien civilizations out there in the Milky Way Galaxy and, when the numbers were finally crunched, concluded that there are 36 of them.
As The Guardian reported, the Drake Equation, a thought experiment that informs the discussion of the number of alien civilizations, has been around for decades. Astronomer Frank Drake postulated that, when considering the number of alien civilizations capable of contacting each other and, potentially, Earth, different factors must be considered. Those factors include the number of new stars that form in a galaxy each year, the number of years it takes for a civilization to evolve the technology necessary to contact other civilizations, and many other things.
In the decades since Drake came up with the equation, the number of potential such civilizations has ranged from 0 to billions, and everything in between.
For Drake, that was kind of the point. His equation wasn't intended to come up with an actual number of alien civilizations. Rather, it was intended to provide parameters for thought and discussion on the topic.
"[The Drake Equation] is more like a tool for thinking about questions rather than something that has actually been solved," said Christopher Conselice, a professor of astrophysics at the University of Nottingham.
However, Conselice and his team put hard data into the Drake Equation and came up with what they believe is a workable number.
Essentially, Conselice's team started from the assumption that, on any habitable planet, it would take about 4 billion years for life to evolve from the primordial stew and into an advanced civilization capable of sending signals, or even craft, into space. In other words, planets like Earth.
Using the age of the Earth as a template, Conselice's team came up with a range of between 4 and 211 planets in the Milky Way that are old enough to have hosted a civilization capable of contacting extra-planetary civilizations. Within that range, Conselice and his team believe that 36 is the most likely number.
"[If intelligent life forms] in a scientific way, not just a random way or just a very unique way, then you would expect at least this many civilisations within our galaxy," he said.
He also noted his belief that if such an alien civilization exists and manages to contact us, evolution would have played out in such a way that the messengers look not unlike human earthlings.
"We wouldn't be super shocked by seeing them," he said.
By Conselice's calculation, the nearest such civilization is 17,000 light-years away. That means that it would take 17,000 years for a signal from Earth to reach that civilization, and another 17,000 years for a response to be received.