Well the new semester has started, and I'm using Brian Garrett's What is this thing called metaphysics? for the first time. I just had some Office Hours time with my student Edgar Colon Melendez, and we got around to thinking about some cosmological issues (I'd say they're cosmological) that I want to write up here (we got around to it starting from discussing modality and possible worlds modeling, although the two topics are, strictly speaking, unrelated).
I'm wondering about the connection between two arguments. The first is an argument from probability logic for the existence of intelligent life on other planets. Maybe someone has a refutation of this argument, but it seems to me to be intuitively compelling. Say there were two black balls on the pool table, you picked up one of them, and it was an eight ball (let's say you know it's possible that not all black balls are eight balls; maybe there are bumper-pool balls around, say). What would be your expectation that the other black ball was also an eight ball? Maybe not much. But now imagine ten black balls on the table, you pick one up (randomly, of course), and it's an eight ball. The sense that some other balls must also be eight balls is much stronger: surely you didn't just happen to pick up the one out of ten? Well maybe. But now imagine a pool table with one hundred million black balls. You pick up one, look, it's an eight ball. Now, sure, it's logically possible that you picked up the only one. But it at least seems (doesn't it?) that it's more likely that they're all eight balls than that you picked up the only one. With a very huge number like that, it looks like you have grounds for assuming that there are other eight balls on the table.
That's our position in regards to the possibility of intelligent life on other planets. It's vanishingly unlikely that our planet, in this obscure corner of the universe, is the only one. More likely, life evolves whenever and wherever the right environmental conditions exist, and has successfully evolved intelligence any number of times.
What I'm wondering is what relationship this reasoning has, if any, to the so-called Anthropic Principle. This argument, a subtle and fascinating one, goes like this: in order for intelligent life to evolve, the universe must be a highly-organized place. Out of all the ways a universe could be, the set of such organized universes is extremely small relative to the larger (total) set. Even so, there is no surprise that this universe is organized, because we are here. So we can be certain a priori that the universe is a (relatively) hyper-organized one. Does this argument cash out the same way that the probability argument for intelligence on other planets does? Can it be used to support the assertion that there must be many universes, with many of those featuring intelligent life?
Maybe not, because it's not so clear what a universe is, or if multiple universes are even possible. Does it matter that there is no possible causal or spatiotemporal relation between universes, the way there is between solar systems?