I don't "believe" in belief.
I don’t “believe” that there is intelligent life on other worlds.
I don’t “believe” that there is not either.
I do “believe” that we don’t know.
I do “believe” that we need to keep searching.
Fri, 9. August 2019
The Impact of Time on Extra-terrestrial Civilisations
There are lots of stars out there in the galaxy - between 100 billion and 400 billion - but how many star systems are actually home to advanced civilisations in the Milky Way galaxy at any particular time?
It's ok for someone to “believe” that the immense number of stars simply translates - inevitably - to a large number of advanced civilisations - but that "belief" is invalid if it fails to understand the immensity of time. After all, stellar evolution will vary from star system to star system.
If that large number of supposed civilisations is spread across (say) the last 10 billion years of stellar evolution in the galaxy, then the average potential number of such civilisations existing at any particular time may well become quite small, depending on how optimistic or pessimistic one is that an advanced civilisation may last.
In that regard I am a pessimist, (which may not go down well with the multitudes who have spent their lives voraciously devouring futuristic science fiction movies).
Here is part of a simple spreadsheet, which took only a few minutes to create:
The age of the Universe is 13.8 billion years (line 5). For ease of discussion, first assume:
1. that no advanced civilisations arose in the first 3.8 billion years (line 6); and
2. that advanced civilisations did arise throughout the remaining 10 billion (line 7) years.
Next, assume, pessimistically (column C):
3a. that 10 million advanced civilisations have existed in that duration (line 8); and
4a. that the average duration of such civilisations is 1,000 years (line 9).
The result of this pessimistic argument (line 10) is that spanning 10 billion years, an average of just one advanced civilisation on average existed in the galaxy at any particular time. 10,000,000 civilisations could rise and fall without ever existing at the same time.
Conclusion: We are alone.
Now make a much more optimistic assumption (column D):
3b. that 20 billion advanced civilisations have existed in that duration (line 8); and
4b. that the average duration of such civilisations is 2,000,000 years (line 9).
The result of this overly optimistic argument is that spanning 10 billion years, an average of 4 million advanced civilisations existed in the galaxy at any particular time.
Conclusion: The galaxy is teeming with advanced civilisations right now.
However, that does not seem to be the case.
I don’t want us to be the only advanced life in the galaxy but I would not rule it out. We live on a very fortunate planet where a lot of very fortunate random events resulted in the very fortunate conditions for primitive life and a very fortunate evolutionary pathway for human existence at this time.
The only thing I know for certain is that over the last sixty years we have dramatically ramped up the size, methodology and sophistication of our Search for Extra-terrestrial Intelligence and have so far come up with – absolutely nothing at all.
That is all the more reason to keep searching.