The New Work
In our paper, Woody and I realized that we could use this giant leap forward to do something that, to our knowledge, had not been done before. We used the new data to say something a little more definite about exo-civilizations.
To accomplish this, we first changed the question.
“How many exo-civilizations exist now?” and focused instead on “How many exo-civilizations have their ever been?”
This approach allowed us to ignore the lifetime term L.
It also allowed us to think differently about the three unknown probabilities involving life (fl, fi, and ft).
Rather that dealing with them separately, our approached focused on all three terms together. That means we were interested in the whole enchilada: the entire process going from the origin of life all the way up to an advanced civilization.
We called our new term the “bio-technical probability,” fbt, and it’s nothing more than the product of the usual life-centric terms in the Drake equation. In the language of math fbt = fl * fi * ft.
By looking at the problem this way – and using the new exo-planet data and rearranging things – our results provide an empirical constraint to a very different question than the one Drake’s equation usually focuses on.
Here is our question:
What would the bio-technical probability per planet have to be for us to be the only civilization that ever occurred in the entire history of the universe?
Putting in our exo-planet date, we found the answer is 10-22 or 1 in 10 billion trillion.
We call this number the “pessimism line,” and you can think about its meaning in a bunch of ways.
First, imagine you had a big bag of Goldilocks zone planets (planets in orbits where liquid water can exist on the surface). Our results says that you’d have to go through 10 billion trillion planets and only find one with an exo-civilization for humans to be unique.
Another approach is to recognize that, until our work, no one really knew what pessimism meant.
Were you a pessimist if, for example, you thought fbt was 1 in a million or 1 in a billion?
Before our paper, there was no way put a firm limit on which values for the life-centric terms in the Drake equation implied we were alone in the deepest sense of the word. What Woody and I found was that if nature, in its infinite wisdom, chooses a value below 1 in 10 billion trillion, then we’re the only civilization ever.
But if nature chooses a number bigger than one in 10 billion trillion then we (meaning life and intelligence and civilization) has happened before.