I just finished “The Eerie Silence” by Paul Davies. Davies is deeply involved with SETI, and so took some time to speculate on the possibility of extraterrestrial intelligence.

It’s a subject I find fascinating, though I recognize that it’s all speculation. Still, it’s fun to think about.

I’ve been influenced by Peter Ward and David Brownlee, who wrote an amazing book called Rare Earth and another called The Life and Death of Planet Earth, and I’ve very much adopted their argument.

The argument goes like this: life itself may be quite common in the universe. After all, life seems to have appeared on our planet as soon as it possibly could have. It would be quite a coincidence if life began here so quickly, but then never appeared anywhere else.

But Davies points out a flaw in this argument. We are not a random sample, but a very special circumstance. We are a place where life has gone from single cells to complexity and intelligence. It took a very, very long time to get there – most of the time that the Earth will be inhabitable. We humans just barely made it, sneaking in under the wire before, in just 1 billion more years, the Sun gets so hot that it sterilizes the planet.

If that is typical, then it is no surprise that we happen to live on a planet where life started quickly. If it hadn’t, if it had taken billions of years instead of millions or less for life to form, there wouldn’t have been time for humans to develop. In the “space” including all those planets that have life, only those on which life started quickly is there any chance of finding intelligence. Naturally, since we’re here to ask the question, we live on one of those lucky early-life worlds.

It’s an interesting argument, and I’m still thinking about it. I think I’ll write about it again.