Carl Sagan bamboozled us about the probability of intelligent life evolving elsewhere. He said there are billions and billions of civilizations in out galaxy.
Reality is different. There's certainly bound to be lots of planets with simple life (bacteria) and possibly many with multi-celled life (such as arthropods, fish, molluscs).
But intelligent life is rare, there's probably fewer than 10 planets, certainly fewer than 100 per galaxy that have advanced life.
It took about 3 billion years for multi-celled life to evolve from simple life on earth, and another 550 million years for intelligent life to evolve. When we look outside at night, do people realize that more than 99% of all the stars we see won't last nearly as long as the sun has because they are burning their hydrogen more rapidly, being larger and hotter?
Only a very few faint stars we can see such as Epsilon Eridani will live as long or longer as the sun, and for most of those there are other reasons why advanced life would not be possible, such as the massive debris disk with an enormous number of collision-creating asteroids around Tau Ceti.


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