Is Anyone Out There

In Science Fiction, alien races are as common as ragweed in September. Yet, although we've been listening for a while with SETI, so far we have detected no signals indicating a technological advanced race in our galaxy. There may be many reasons for this. We may be listening on the wrong frequency, the signals may be too weak to detect, something is blocking the signals, and so forth. I'm discounting the claims of UFOologists since no credible evidence has shown that an alien race has entered our solar system. Does this mean we are alone in the galaxy? A provocative question. The odds are probably that we are not. So how do we estimate the number of advanced civilizations that actually exist? That's what I intend to discuss in this article.

In the first place, there are a hundred billion stars in the galaxy. That would seem to indicate that the odds were heavily in favor of many advanced civilization existing. The question becomes what is the likelihood of an advanced civilization arising on any particular star system. A radio astronomer by the name of Frake Drake came up with the following formula for estimating the number of advanced civilizations: N = R* x fp x ne x fl x fi x fc x L

N is the number of advanced civilizations.

R* is the average rate of star formation. New stars are being born all the time. So the new additions must be calculated into the formula. Astronomical estimates vary from 2 to 20 a year.

fp is the fraction of stars having planetary system. Until recently, this number would be considered to be a low one by many astronomers. Recently, however, they've discovered that almost all stars have planets. Therefore, this number should be about 95%.

So far, we're doing pretty good. It would seem to be a lot of aliens around. But the next numbers whittled the estimate down quite a bit.

ne is the number of planets with a suitable environment that life could come into being and develop. In our own solar system, the only place that we've found is earth. The planet cannot be too cold or too hot. The moons of the outer planets are too cold, Venus is too hot. It must have liquid water. Mars, at this time, is too dry. It had liquid water in the past. Did life develop there and die out? That's what we're investigating now with our probes.

As far as an estimate for ne, all the planets that we've detected around other stars have been gas giants, which cannot possibly sustain life. But that does not mean that small earth like planets do not exist. In fact they probably do, but are too small to detect. Some moons of the gas giants may lie in a habitable zone. Still, out of a hundred billion stars, it would seem to me that at least ten percent would have earth like planets with the right ingredients to form life.

fl is the fraction of habitable planets where life actually came into being. Since modern biology seems to conclude that life would form where the conditions allow it. That would seem to make this number 100%. Not quite. The age of the earth is around 4.5 billion years old. The oldest fossil evidence for life is 3.5 billion years. This may mean that it took a billion years for life to develop. Many stars do not last that long. In fact, at least half expire in much less time. As a result, my guesstimate for this figure would be 50%.

fi is the fraction having intelligent life. This is a tough one. It took about 3.5 billion years for life to evolve into us. Along the way, there were several times when the prevalent life was almost wiped out; some say by giant meteors crashing into earth. What if the dinosaurs had not been wiped out by some catastrophe? Would they have developed intelligence? No one knows. It is very possible that many planets in the galaxy have life forms, but not with enough intelligence to develop sophisticated technology. This must be a very small number.

fc is the fraction having advanced technology. Again, human beings evolved from ape-like creatures around a million years ago. It took us to a million years to develop a technology capable of space travel and radio telescopes. This number is the fraction of intelligent beings having this capability at any given time.

A small digression. Stellar distances are so great that chances are that if we did receive a signal from an alien species, the signal could be as much as 50,000 years old. The aliens who broadcast it might have perished eons ago.

Which brings us to L, which is the average lifetime of an intelligent species. During the 1950s we came close to destroying ourselves in an atomic war. Many believe that we will pollute ourselves to extinction. A comet or asteroid could crash into the earth and destroy us. A terrible unstoppable plague could wipe us out. As you can see, intelligent species can perish. How often this happens is anyone's guess. Once advanced technology is reached, how long does an intelligent species last? Millions of years? Thousands? Hundreds? Tens? Your guess is as good as mine. So far we've managed to survive the twentieth century. Can we survive the twenty-first?

For more information on Drake's equation and the possibility of life in other star systems, go to the web site Astrobiology, which has, among a wealth of information, a calculator where you can plug in various numbers to determine how many possible alien civilizations exist in the Milky Way galaxy using various parameters.