Flies and Fine-tuning

Multiverses

Charles: Consider our universe. It seems ‘fine tuned’ for life. Many of the fundamental dials of our universe need to be set ‘just so’ within an exceptionally small degree of tolerance for our universe to remain ‘life friendly’. Assuming these values can range fairly freely, that we arrived at this combination is ludicrously unlikely ‘just by chance’. If God exists though, we’d expect a universe he creates to be life friendly, because life is part of his design plan. So the fine-tuning of our universe confirms Theism over Atheism.

Debbie: Several problems. Good metaphysical sceptics like me won’t be happy to say how, or in what sense, the relevant values can ‘range freely’ (maybe they’re necessary). Ignore that though – I suspect these worries can be answered. I’m more worried about a multiverse. Take some sensible principle like “all possible worlds exist” or “every possible combination of these values exist”. If that is true, then we shouldn’t be surprised at all to see that we exist, even in a universe finely tuned (or even uniquely tuned) for life.

Charles: That seems ad hoc to me. What reason is there to suppose a multiverse, but for Atheists to explain away fine tuning data?

Debbie: Ad hoc isn’t the be-all and end-all of explanatory virtue. After all, we all should develop and modify hypotheses in light of new data. I believe some think many worlds because of certain mysteries of quantum mechanics, so for these people it isn’t an ad hoc addition to protect their atheism. Regardless, I see no reason to deny a multiverse, even if I don’t have much reason to affirm one. I should leave it as a live option. Yet, if this is a live option, then the confirmation of Theism over Atheism seems to be lacking: fine tuning becomes unsurprising because it is unsurprising on a multiverse, and that itself is unsurprising given Atheism.

Charles: Maybe so. But even if we get to ‘unsurprising’, that isn’t as good as exactly what we’d expect. Given Theism, fine tuning is exactly what we’d expect, whilst on Atheism, it is (given the live option of a multiverse) merely unsurprising. Suppose I know of two urns, one filled with white balls, and one filled with a fifty-fifty mix of white and red. I draw out a white ball. That’s unsurprising on the half-and-half urn, but exactly what you’d expect on the all-white urn. So that acts to confirm the latter.

Debbie: Sure, but I have more than a few worries about whether we should really expect life given Theism. I’m not convinced perfect beings would be motivated to create anything at all. These worries are insiginificant if you can show the fine tuning data is ludicrously unlikely on Atheism, but spring to the forefront if it’s only unsurprising.

Leave that aside, though. I think there’s a bigger worry – I don’t the argument works even if we restrict ourselves to a single universe. Continue reading