I’m confused about how satisfactory a multiverse is as an alternative explanation for the fine-tuning of our universe (alternative to God, that is).
My initial intuition about this is that it is a perfectly satisfactory explanation. It looks like we can justify this on Bayesian grounds by noting that the probability of the universe we’re in being fine-tuned for intelligent life given that there is a multiverse is nearly 1. The probability of fine-tuning given God is also presumably nearly 1, so the observation of fine-tuning shouldn’t push us much in one direction or other.
(Obligatory photo of the theorem doing the work here)
But here’s another argument I’m aware of: A firing squad of twenty sharpshooters aims at you and fires. They all miss. You are obviously very surprised by this. But now somebody comes up to you and tells you that in fact there is a multiverse full of “you”s in identical situations. They all faced down the firing squad, and the vast majority of them died. Now, given that you exist to ask the question, of COURSE you are in the universe in which they all missed. So should you be no longer surprised?
I take it the answer to this is “No, even though I know that I could only be alive right now asking this question if the firing squad missed, this doesn’t remove any mystery from the firing squad missing. It’s exactly as mysterious that I am alive right now as that the firing squad missed, so my existence doesn’t lessen the explanatory burden we face.
The firing squad situation seems exactly parallel to the fine-tuning of the universe. We find ourselves in a universe that is remarkably fine tuned in a way that seems extremely a priori improbable. Now we’re told that there are in fact a massive number of universes out there, the vast majority of which are devoid of life. So of course we exist in one of the universes that is fine-tuned for our existence.
Let’s make this even more intuitive: The earth exists in a Goldilocks zone around the Sun. Too much closer or further away and life would not be possible. Maybe this was mysterious at some point when humans still thought that there was just one solar system in the universe. But now we know that galaxies contain hundreds of billions of solar systems, most of which probably don’t have any planets in their Goldilocks zones. And with this knowledge, the mystery entirely disappears. Of course we’re on a planet that can support life, where else would we be??
So my question is: Why does this argument feel satisfactory in the fine-tuning and Goldilocks examples but not the firing squad example?
A friend I asked about this responded:
if you modify the firing squad scenario so that you don’t exist prior to the shooting and are only brought into existence if they all miss does it still feel less satisfactory then the multiverse case?
And I responded that no, it no longer feels less satisfactory than the multiverse case! Somehow this tweak “fixes” the intuitions. This suggests that the relevant difference between the two cases is something about existence prior to the time of the thought experiment. But how do we formalize this difference? And why should it be relevant? I’m perplexed.