 According to the multiverse hypothesis, there are multiple universes, some of them radically different from our own. Many of those who believe that fine-tuning for life requires some theoretical response regard it as the main alternative beside the designer hypothesis. The idea that underlies it is that, if there is a sufficiently diverse multiverse in which the conditions differ between universes, it is only to be expected that there is at least one where they are right for life. As the strong anthropic principle highlights (see  Section 3.2),  the universe in which we, as observers, find ourselves must be one where the conditions are compatible with the existence of observers. This suggests that, on the assumption that there is a sufficiently diverse multiverse, it is neither surprising that there is at least one universe that is hospitable to life nor—since we could not have found ourselves in a life-hostile universe—that we find ourselves in a life-friendly one. Many physicists (e.g., Susskind [2005], Greene [2011], Tegmark [2014]) and philosophers (e.g., Leslie [1989], Smart [1989], Parfit [1998], Bradley [2009]) regard this line of thought as suggesting the inference to a multiverse as a rational response to the finding that the conditions are right for life in our universe despite the required fine-tuning.