The most-discussed objection against this argument is that it commits the inverse gambler's fallacy, originally identified by Ian Hacking. This fallacy consists in inferring from an event with a remarkable outcome that there have likely been many more events of the same type in the past, most with less remarkable outcomes. I discuss several suggested analogs to the problem of the fine-tuned parameters. Ultimately, as I argue, established standards of rationality may just not allow one to decide whether the standard fine-tuning argument for the multiverse commits the inverse gambler’s fallacy or not. Some of the considerations in this chapter, as explained along the way, are relevant to the debate about the Fermi paradox.

This chapter continues the discussion of the standard fine-tuning argument for the multiverse, switching to the language of Bayesianism. After highlighting the desideratum of motivating a non-negligible (ur-) prior for the multiverse, I assess a worry, due to Cory Juhl, about belief in the multiverse, as based on the standard fine-tuning argument for the multiverse: that, even if the inverse gambler's fallacy charge could be rebutted, such belief would inevitably rely on illegitimate double-counting of the fine-tuning evidence. I argue that this concern can be assuaged, at least in principle: it is coherently possible for there be empirical evidence in favor of some specific multiverse theory – and thereby, derivatively, for the generalized multiverse hypothesis – whose evidential impact is independent of the fine-tuning considerations. The probabilistic formalism is also used to clarify why it is so difficult to determine whether the standard fine-tuning argument for the multiverse is fallacious: the difficulty can be linked to an ambiguity in the background knowledge based on which the impact of the finding that the conditions are right for life in our universe is assessed.