The Universe is a Big Place

I have read that there are something like 100 billion to 1000 billion stars in our galaxy, and there are perhaps something like 100 billion to 1000 billion galaxies. That is big! Lets take the smaller estimates of about 100 billion galaxies with about 100 billion stars each.

Assume that one out of 100,000 stars has a planet that has developed life. That doesn't seem too large a number. Astronomers have found lots of planets on the stars that they can see well enough, and indeed, have detected a planet in the zone that should have liquid water circling another star. I have never read any analysis that suggests that the solar system is somehow special in the materials it contains so as that earth is likely to be exceptional in having developed life.

Assume that one out of 100,000 planets that has developed life, develops intelligent life. Our planet has developed a fair number of more or less intelligent species -- not only man, but other primates, dolphins and wales and some species of birds are reasonably intelligent. Remember that the universe is billions of years old, and there has been a long time for relatively advanced brains to develop into true intelligence.

Under these assumptions, one out of 10 billion stars would develop at least one intelligent species. Thus the average galaxy might have ten such planets. The universe, with 100 billion galaxies, would contain 1,000 billion, or a trillion, planets that developed intelligent life!

Under these assumptions, mankind might never succeed in finding another intelligent species in the universe. We might never be able to search other galaxies, nor indeed to search our own to discover one of the few stars that had a planet with an intelligent species during the lifetime of our own.

On the other hand, if there are 1000 billion planets out there that did develop intelligent species, what is the probability that our species, with its short lifespan and shorter historical record, is the smartest one? Indeed, I doubt that there is a 50-50 chance that we are in the top half of the crowd.

Someone out there might come looking for us!