Link to Drake Equation Calculator
With all of the new Kepler and other information on the prevalence of planets in our galaxy and universe you can have fun estimating the number of possible alien civilizations at the current time
Click on the image or this link to see the calculator
here is version 2
Cool, but sort of useless.
There are too many approximations that enter in the equation, the flakiest being L, the average lifetime of communicable civilizations. We've been at this "communicable" stage for barely 100 years, with NO experience whatsoever in advanced civilization longevity...
It seems that there are a ton of planets, most likely enough water and habitable zones and plenty of life - the fraction that becomes intelligent enough to make radio and other noise, invent and want space travel is the big unknown.
The first five terms are a pretty sure bet.
As you go down the list of factors, from fi to L they become more and more approximate.
I like and book marked both pages for future reference.
Though from n subscript e to L are approximations but it is good to fiddle around with those factors to give the likelyhood of space faring races.
There is one factor missing that is the number of stars that have been born and died since the formation of of the galaxy that could have harboured the birth of a life form on it.
Our own sun is only 3 to 4 milliard years old. While the universe has been around for at least 13 milliard years!
Hey! Don't confuse me with your milliards =)
That is what I was brought up with and they use it in this neck of the woods. Actually billions confuse me :-( I have to keep figuring is it one thousand million or is it one million million.
You guys are giving me a headache :-)