Estimating Galactic Population – Introduction
In 1960 Frank Drake introduced an equation to estimate the number of advanced technological civilizations the Milky Way. By his calculations, the Milky Way should be teaming with advanced civilizations. Enrico Fermi’s response was along the lines of “So where are they?” And thus began the long debate about what numbers to stick into the Drake equation. Then there is also the debate about the usefulness of the Drake equation. One thing is certain, the Drake equation was useful to the Search for Extra-Terrestrial Intelligence or SETI.
The detractors ask what good is the Drake Equation since it can produce a very wide range of reasonable looking results, from we are alone to we have several neighbors within 100 light years. The way I see it is that it is a good first attempt to a model, or hypothesis. As such it informs us on what numbers we are missing and generally does a pretty good job of laying out what the important variables are. A good model informs us about a particular aspect of the universe, a great model then makes accurate predictions. The Drake equation is a good model, and the only thing keeping it from being a great model is figuring out how to fill in the variables.
On the argument about how frequent intelligent life is, I believe that each part of our existence is typical, median, or average. Sol is a pretty average star, our Solar System will be pretty average among planetary systems, and so on and so forth. But when you look at just how many factors are implied by the Drake equation, one finds that Earth is pretty special. 0.5^20 is only 9.54e-7. We know that in our own solar system planets with intelligent life are only 12.5% of planets, and there are more than 20 factors implied. So we could end up as something rare or even unique even though any given aspect is pretty typical.
I would like to point out that I disagree with huge chunks of the Rare Earth Hypothesis. Mostly for what I believe are pretty good technical criticisms, and since those criticisms have been made by much smarter people than me, I feel confident believing that way.
In part 1 I introduce my version of the Drake equation, and in remaining parts I’ll give my reasoning behind my choice of values for each major factor, and describe some of the constituent factors that go into it.
And remember – the one fact that can be drawn from the Drake Equation is just how little we know about our Milky Way and life within it.