Can the Aliens Talk to Us? This next bit is part of what separates the Drake equation from general thought experiments about the existence of life in the cosmos. It asks how many intelligent civilizations come up with technology that lets them broadcast evidence of their existence into space (purposefully or not). We’ve been sending out radio waves for decades, and we’re only getting louder. It’s of course possible for an intelligent civilization to remain quiet, but we’re interested in the ones we can communicate with, which means they have to give some signs.



The last factor considers how long these civilizations hang around. One that exists for only ten years before an asteroid destroys it, or destroys itself by nuclear war, will be harder to find than one that broadcasts for hundreds, thousands, or even millions of years. During the Cold War, many argued that it looked like our civilization — and therefore most others? — might not make it past the nuclear age. The window between developing radio technology and nuclear weapons was pretty brief for us.



On the other hand, you can argue that once a lifeform escapes off-world and starts to colonize other planets it becomes much harder to wipe out as an entire civilization. One asteroid or plague wouldn’t do it. So maybe those civilizations quickly become immortal.



If you combine all these numbers, you can end up with conservative estimates that give a total number less than 1; as in, we are alone in the universe. More optimistic numbers can yield tens of millions of possibilities. Drake’s original estimates were between 20 at the low end, and 100,000,000 at the upper end. So while we’re making progress on some of these figures, we’ve still got a long way to go.



Korey Haynes is an Astronomy contributing author.