In an earlier article titled “A Conversation With God” I raised some interesting questions about the number of planets that the god in the story was required to monitor. The “galaxy cluster” that he claimed was his responsibility is what astronomers call the “local group.” (See Note) It consists of about 30 galaxies, some of which are “dwarfs.” Our galaxy, the Milky Way, and the Andromeda galaxy are huge…each containing from 200 to 400 billion stars. A conservative estimate would put the total number of stars in the local group at around a trillion…that’s 1012 or a thousand billion stars. Monitoring them all would indeed be a huge job.
Not all of those stars have planets, and even fewer of them have planets in the habitable zone capable of supporting life. From recent studies of extrasolar planets it appears that most of them orbit stars similar to our Sun…that is, main sequence stars of spectral categories F, G and K. These three categories comprise roughly 25% of the total star population.
A tougher question is: How many of those planets could support life? Nobody knows the answer to that question, but a quarter of a trillion (250 billion) stars that might have a planet with life gives us a lot of chances for it to happen. We certainly know that it happened in one case.
Just for fun, let’s say that one planet in a thousand could support life. Then there are 250 million planets in our local group that might have a civilization like ours! Some of them might have developed long before the earth’s life forms evolved. Others might still be in their infancy, simple microbial organisms, hundreds of million years away from advanced forms like those on the earth.
This makes it clear why the Search for Extraterrestrial Intelligence (SETI) has failed (so far) to detect any emanations from intelligent life forms out there. The probability of another civilization capable of transmitting signals to us in the narrow time window defined by our ability to understand their transmissions is vanishingly small. Still, it’s worth the long-shot effort.
But consider the (alleged) God’s task to monitor those 250 million planets. He better have a very fast spaceship to travel between them! But, of course, most believers would reject this idea completely because it assumes that there are a number of Gods monitoring all the other galaxy clusters. Nonsense! There is only one God! Okay, how many planets does he need to monitor?
Nobody knows how many stars there are in the Universe. Estimates range between 1022 and 1024. If 25% of those stars have planets, and 0.1% of those have planets with life, then God needs to watch over at least a billion billion planets!
That should keep him busy!
The local group of galaxies (30) is 10 million light years in diameter.
My estimate of number of stars in local cluster: 3 TRILLION (3 x 1012)
Number of stars in Milky Way (our galaxy) – 200-400 BILLION
Number of stars in the Universe – 1021
That’s ten billion times ten billion times ten.
 This assumes that life forms will be carbon-based and similar to earth life forms. It may be that different life forms can evolve in quite different environments.
Bert Bigelow graduated from the University of Michigan engineering school, and then pursued a career in software design. He has always enjoyed writing, and since retirement, has produced short essays on many subjects. His main interests are in the areas of politics and religion, and the intersection of the two. Many of his writings are posted on his web site, bigelowbert.com. You can contact him at firstname.lastname@example.org.