How Many Alien Civilizations Exist In Our Galaxy?
On the equations and odds of alien intelligence
The Drake Equation goes something like this. First, you work out how often new stars are born. Then you estimate how many of them have habitable planets, ask how many evolve life, guess a few more parameters, and eventually arrive at the number of advanced civilizations that must exist in our galaxy.
Everyone who does this reaches a different answer. Some people think the number must be low – it cannot be lower than one, of course, since we are here, but it might not be much higher than that. Others think there could be ten million civilizations out there, and that our galaxy might be teeming with intelligent beings.
When it was first proposed in the 1960s, the Drake Equation was intended as a way to figure out how likely we were to detect a radio message from the stars. If there were few civilizations in the galaxy, such a message would be unlikely. Even if someone was sending one, they would probably be far from us and the signal too weak to detect. But if there were many, the odds of spotting a message might be far higher.
Frank Drake, the man who proposed the equation, estimated the number of civilizations to lie somewhere between twenty and fifty million. Which, of course, made it rather useless. If there are only twenty intelligent civilizations, then surveys of radio signals are a waste of time. If there are fifty million, then we would probably have seen some sign of them already.
As a thought exercise, though, the Drake Equation has its benefits. It does not, and cannot, promise to offer an accurate result. But it did start a conversation, and it began a long process of trying to pin down the parameters that determine how common life is, and how widespread intelligence might be.
Today - since we still, after more than half a century of looking, have seen no sign of civilization beyond Earth - it hints at where the bottlenecks to intelligence might lie. And that, regardless of the answer we arrive at, means the equation is still worth looking at.
