It has come to my attention that some of you doubt the existence of aliens, at least SF aliens. SF aliens are local guys, within 1000 light years. They usually have bug eyes and arrive at earth with a desire to mate with our women or use us as a food source.

If there are aliens why haven’t we met them? The physicist Enrico Fermi, asked the question “Where are they?”, and so this is called Fermi Paradox.

Frank Drake quantified the Fermi question in the form of his famous Drake equation that calculated the number of possible intelligent civilizations that are transmitting signals we might be able to detect in the galaxy. He estimates that there might be as many as 100,000 alien civilizations, but you can be very pessimistic and come up with only a few with only a small change to the numbers.

I have a variation on the Drake Equation that estimates the number of aliens in our neighborhood.

Keith’s Special Drake equation is given here:

N = number of local alien cultures.
P = fraction of stars with planets. (nearly 100% according to latest studies)
N = number of planets per solar system that might support life. (usually more than 1)
L = fraction of these planets that actually do develop life. (Some think 100%)
I = fraction of planets with life that go on to develop intelligent life. (Maybe all of them.)
C = fraction of alien cultures that make themselves know by traveling or transmitting signals. (figure red planets don’t spend the money, but blue planets might – 50%)
E = the life expectancy of a culture – how long the culture survives and makes itself known. (I like to think they avoid blowing themselves up for a few thousand years.)
T = average length of time that planets can support life. (a billion years maybe more)
R = radius of our neighborhood (We’ll use 1000 light years)
D = star density (.003 stars per cubic light year)

N= D*R*R*R*pi*P*N*L*I*C*E/T

First the number of stars within 1000 light years comes out to be about 9.4 million. That’s the D*R*R*R*pi part.

My optimistic estimate of the number of planets says that P*N*L*I*C might be as much as 100%.

The sad part is that many cultures might destroy themselves before they get around to saying hi. For E, I am going to say only 1000 years.

And for T, I am going to estimate one billion. Some stars don’t last that long. The Earth has had life for about 4 billion years. I think that intelligent life doesn’t occur until a few billion years after life begins, so I think that we might live in a time when there are many more intelligent cultures than there were a billion years ago.

So 9.4 million times 1000 divided by a billion is 9.4.

Within a thousand light years from us there are about 9 alien cultures currently active that we might be able to contact.

Don’t argue with me. I was a math major.