Star date: 09:27:99

Yes, but are They Looking BACK?

There are perhaps 400 billion stars in our galaxy. You can look up at stars, and see thousands of them at one time, but how many beings in our galaxy are sitting on their home worlds, staring back at a bright, distant dot in the sky, around which circles a tiny little rocky world named Earth?

Certainly, there is no way to know for sure, but there is a way to estimate the number of intelligent civilizations present in our galaxy, or in the universe as a whole. The main part of the equation is called the Drake equation, named after the astrophysicist Frank Drake, who first developed it.

Since we are trying to determine just the number of civilizations in our galaxy, we will begin by only considering this number of stars. This leaves us with 400 billion or so possible star systems. How many of these have planetary systems? Planets now seem to be very common. Dozens of planets have been found orbiting around other stars, but let us pick what would seem to be a very conservative estimate, and say that half of the stars we can see contain planetary systems. This leaves us with 200 billion or so planetary systems.

The next thing we must consider is the average number of planets per planetary system. Let us again use a conservative estimate and say that our solar system is an unusually large system, and the average family of planets consists of only five members. This leaves us with one trillion possible home worlds for extraterrestrial life.

From here, we must determine the percentage of these worlds which develop any form of life whatsoever. The simplest forms of life on Earth are bacteria, consisting of single celled organisms. These bacteria also have no central nucleus, and thus are known as prokaryotic cells. This simply means "before a nucleus".

The cells in our bodies are known as "eukaryotic cells", meaning "true nucleus". Perhaps the most famous of the prokaryotic life forms is E. Coli, a simple bacteria, which live inside all human intestines, and we could not live long without them. They are perhaps the simplest things alive. Even though they do not have a nucleus, even these simplest of life forms still possess, and depend on, DNA. Without a true nucleus to gather together in, the DNA in these types of cells still huddle together in a loose formation known as a nucleiod region. DNA (deoxyribonucleic acid) is the ultimate blueprint of life and it is capable of reproduction (with the help of some other molecules).

If we consider reproduction to be essential to define any life, no matter how strange, perhaps we should just try to find the number of planets which develop something analogous to DNA. The building blocks of DNA are amino acids, which are similar to sugar in structure. Amino acids are not by themselves alive, but they are the bricks which make up the house we call life. Amino acids are everywhere we look in space. There are great dust clouds of black soot , which would engulf our solar system many times over, floating between the stars and they are awash with amino acids.

Let us say that only one percent of planets develops some chemical capable of reproduction. This leaves us with 10 billion worlds, whose parent stars are within our galaxy, where life has begun at least once.

The universe may be inundated with life, but perhaps it is just bacteria-like simple life, or at most, lichen. Maybe intelligence is a rare thing indeed, and perhaps only this once has gotten past the stage of say, fish. I find this highly unlikely. It seems logical that the forces of evolution and the laws of natural selection would work on any world whose species struggled to obtained what was needed from the limited resources available. Let us say intelligence developed on only one percent of these worlds. That would still leave us with 100 million odd societies which at one time, looked back at us.

The stars DO move relative to one another, but let us assume that we are in a period of average star density in our area, which will allow us to ignore that factor.

Finally, how much of the time during a planets life is there intelligent life looking up at the stars? For our world, it is a very small percentage; about 2/10,000 of one percent of the history of the Earth. If that is a typical figure for the percentage of time spent looking with some degree of higher intelligence at the stars, then there are about 22,000 extraterrestrial societies, right now, in our galaxy. However, our species is young, and curious, and our written history extends only 10,000 years. Many species exist for a million years or more. If this is a better figure, than intelligence looks up from a planet which has developed life for perhaps (using our own solar system as an example) .02 % of the time. It still would make the number of societies in our galaxy right now around 2.2 million.

Clear skies, and good viewing.

"Understanding is joyous" - Carl Sagan