FEATURE: The Drake equation, How many civlised planets are there in the Galaxy

Forty years as an astronomer have not quelled my enthusiasm for lying outside after dark, staring up at the stars. It isn't only the beauty of the night sky that thrills me. It's the sense I have that some of those points of light are the home stars of beings not so different from us, daily cares and all. Who look across space with wonder, just as we do?

Frank Drake

The Drake equation is a famous equation for trying to estimate how many Technological civilisations there might be in the universe, when you look at the size of our galaxy with its billions upon billions of stars around witch many exoplantes orbit the fact is that we simply cannot be alone as the only sentient beings in the cosmos.  However as The Fermi Paradox asks why, given the seemingly endless amount of stars in the night sky, we have not heard from another intelligent race yet.  The simple answer is we don’t know.  Now don’t get me wrong on this I don’t believe that mankind is visited by little green man or even that what happened at Roswell was anything other than a botched military exercise but, I like many better men before me including the grate Carl Sagan himself believe that we are not alone.  The only question is how many other species are out there, and, this is where the drake equation comes in.

The man himself, Frank Drake.

First put forward by Frank Drake in 1961 the equation identifies the specific factors thought to play some role in the development of such civilizations.  There is no unique answer to the equation but it is a generally accepted tool amongst the scientific community to examine these factors.

The equation runs like this:

Where N = the number of civilizations in our galaxy with which communication might be possible.
R* = the average rate of star formation per year in our galaxy.
fp = the fraction of those stars that have planets.
ne = the average number of planets that can potentially support life per star that has planets.
fℓ = the fraction of the above that actually go on to develop life at some point.
fi = the fraction of the above that actually go on to develop intelligent life.
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
L = the length of time such civilizations release detectable signals into space.

to give an answer to this equation I'm going to hand over to a much better man than myself.  the late grate Carl Sagan: