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solipsist comments on Open thread for December 9 - 16, 2013 - Less Wrong Discussion
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I don't think this is frightening. If you thought life couldn't have arisen more than 3.6 billion years ago but then discover that it could have arisen 13.8 billion years ago, you should be at most 4 times as scared.
The number of habitable planets in the galaxy over the number of habituated planets is a scary number.
The time span of earth civilization over the time span of earth life is a scary number.
4 is not a scary number.
If it were just a date, then, yes, a factor of 4 is lost in the noise. But switching to panspermia changes the calculation. Try Overcoming Bias [Added: maybe this is only a change under Robin Hanson's hard steps model.]
It changes my epistemic position by a helluva lot more than a factor of 4. If an interstellar civilization arose somewhere in the universe that is now visible, somewhere in a uniform distribution over the last 3.6 billion years, there's much smaller chance we'd currently (or ever) be within their light cone than if they'd developed 13.8 billion years ago.
It's the scariest number.
It's potentially scary not because of the time difference, but because of the quantity of habitable planets. It's understood that current conditions in the Universe make it so that only relatively few planets are in the habitable zone. But if the Universe was warm, then almost all planets would be in the habitable zone, making the likelihood of life that much higher.
As I said in my reply to JoshuaZ though, the complication is that rocky planets were probably much rarer than they are now.