Minor issue—for us to see a signal from “far away”, the signal needs to have been sent “long time ago” (naively you’d say that a signal from 7 billion light years away needs to be sent 7 billion years ago, but with expansion that’s not quite true, so I’ll just stick with “far away” and “long ago”).
Now, the probability of new intelligent life evolving should be smaller “long ago”. At least, there used to be fewer metals, so, fewer rocky planets, fewer possible chemical compounds (and before that there were no planets at all). No idea what that probability distribution looks like and how it would be corrected for the fact that there is “more” space “far away”. My point is that signals from halfway across the observable universe could be very unlikely.
I’m aware of this. I agree that very old life is less likely (I’m a bit skeptical about our a priori ability to judge the relative merit of different conditions to form life, but the anthropic argument is pretty simple and seems solid). I’m still happy to start with “halfway across the universe.”
Minor issue—for us to see a signal from “far away”, the signal needs to have been sent “long time ago” (naively you’d say that a signal from 7 billion light years away needs to be sent 7 billion years ago, but with expansion that’s not quite true, so I’ll just stick with “far away” and “long ago”).
Now, the probability of new intelligent life evolving should be smaller “long ago”. At least, there used to be fewer metals, so, fewer rocky planets, fewer possible chemical compounds (and before that there were no planets at all). No idea what that probability distribution looks like and how it would be corrected for the fact that there is “more” space “far away”. My point is that signals from halfway across the observable universe could be very unlikely.
I’m aware of this. I agree that very old life is less likely (I’m a bit skeptical about our a priori ability to judge the relative merit of different conditions to form life, but the anthropic argument is pretty simple and seems solid). I’m still happy to start with “halfway across the universe.”