Philip Goff has an article in Scientific American, looking at one popular rational for the multiverse, the anthropic principle, or argument from fine tuning:
We exist, and we are living creatures. It follows that the universe we live in must be compatible with the existence of life. However, as scientists have studied the fundamental principles that govern our universe, they have discovered that the odds of a universe like ours being compatible with life are astronomically low. We can model what the universe would have looked like if its constants—the strength of gravity, the mass of an electron, the cosmological constant—had been slightly different. What has become clear is that, across a huge range of these constants, they had to have pretty much exactly the values they had in order for life to be possible. The physicist Lee Smolin has calculated that the odds of life-compatible numbers coming up by chance is 1 in 10229.
Physicists refer to this discovery as the “fine-tuning” of physics for life.
Goff goes on to discuss the idea that if we live in a multiverse, where the laws of physics vary between universes, then our improbable luck in having things just right for life doesn’t seem so improbable anymore, but the result of selection. We have to be in one of the few universes right for life, because if we weren’t, we wouldn’t be here to observe that we are.
But Goff, citing arguments from probability mathematicians, argues that this is a case of the inverse gambler’s fallacy, the idea that since something improbable just occurred, it must be just one of numerous outcomes. It’s the opposite of the regular gambler’s fallacy, that since your luck as been bad all night, you’re due for a lucky break. But for any particular instance of a bet, the probability of the outcomes remain the same.
Steven Novella replies that Goff and the mathematicians are engaging in the lottery fallacy. If you bought a lottery ticket last night, and wake up this morning to discover you’ve won, does that require any special explanation? No. Somebody was going to win, and it turned out to be you, as unbelievable as it might feel.
Novella concludes that either there is some deeper reason why the laws of physics are what they are, or we live in a multiverse and have just won the lottery. (Novella also addresses the issue about whether God or some other intelligence amounts to that deeper reason, but points out the problems with that solution.)
Personally, fine tuning arguments have never been that interesting to me. Certainly the universe appears to be fine tuned for life and us, at least from a certain perspective, but that has always struck me as looking at it backwards. I think the actual reality is that we, and all of life, are fine tuned for the universe. Which makes sense, since we evolved in it. If we had evolved in a different universe, we would be very different.
But, the argument goes, without the fine tuning, nothing like the self replicating patterns we call life could have evolved. My issue with this goes back to the quoted paragraph above, and the idea that physicists can meaningfully talk about what the universe would be like under different laws. Sean Carroll made the point a while back that physicists can’t derive the periodic table of elements from the Standard Model.
Any calculations about what the universe might be like under different laws or constants are going to involve a lot of simplifying assumptions. Every assumption is an opportunity to be wrong. Which means my trust in these types of analyses is pretty low. All I think we can really take from them is that the universe would be radically different with different laws. We should be leery of confident conclusions that complex patterns wouldn’t emerge from any of those alternatives.
Life in another universe would be unimaginably strange, but the idea that it could only exist if that universe were like our own strikes me as pretty anthropocentric, which seems strangely appropriate when we’re talking about something involving the anthropic principle.
So, while I think there are scientific reasons to find certain types of multiverses plausible, I’ve never found this particular line of reasoning compelling. But maybe I’m missing something?