In a Scientific American article titled “Our Improbable Existence Is No Evidence for a Multiverse,” Philip Goff argues it’s faulty reasoning to conclude from the extraordinarily improbable fine-tuning of our universe that a multiverse exists.
The hope is that [the multiverse] allows us to give a “monkeys on typewriters” explanation of the fine-tuning. If you have enough monkeys randomly jabbing away on typewriters, it becomes not so improbable that one will happen to write a bit of English. By analogy, if there are enough universes, with enough variation in the numbers in their physics, then it becomes statistically likely that one will happen to have the right numbers for life.
He argues that this kind of reasoning employs the inverse gambler’s fallacy and then offers this analogy to show that the multiverse explanation does not explain the thing that needs explaining:
Consider the following analogy. You wake up with amnesia, with no clue as to how you got where you are. In front of you is a monkey bashing away on a typewriter, writing perfect English. This clearly requires explanation. You might think: “Maybe I’m dreaming…maybe this is a trained monkey…maybe it’s a robot.” What you would not think is “There must be lots of other monkeys around here, mostly writing nonsense.” You wouldn’t think this because what needs explaining is why this monkey—the only one you’ve actually observed—is writing English, and postulating other monkeys doesn’t explain what this monkey is doing….
Given how unlikely it is that an ordinary monkey would come up with “I love how yellow bananas are” just by randomly bashing away, you might suspect some kind of trick. What you would not conclude, however, is that there must be many other monkeys typing rubbish. Again, what you need explaining is why Joey [i.e., this monkey] is typing English, and the postulation of other monkeys doesn’t explain this. By analogy, what we need explaining is why the only universe we’ve ever observed is fine-tuned, and the postulation of other universes doesn’t account for this.
Read the full article to see his responses to anticipated objections (e.g., the claim that the “selection effect” explains why we see a universe fine-tuned for life—that we should not be surprised we’re observing the kind of universe where observation by living beings is possible).
His conclusion:
The reason some scientists take seriously the possibility of a multiverse in which the constants vary in different universes is that it seems to explain the fine-tuning. But on closer examination, the inference from fine-tuning to the multiverse proves to be instance of flawed reasoning. So, what should we make of the fine-tuning? Perhaps there is some other way of explaining it. Or perhaps we just got lucky.
Perhaps there is some other way of explaining it, indeed.