Some scientists or philosophers argue that multiverse theories are unfalsifiable and thus not scientific. However, some advocates of multiverse theories have recently argued that although the multiverse is not observable, multiverse theories are indeed falsifiable in principle. Therefore, they share similar features with a conventional scientific theory. On the other hand, the proposals of an epistemic shift and nonempirical theory assessment have possibly revived the discussions of the scientific nature of multiverse theories. In this article, I revisit the falsifiable arguments (...) made by the advocates of multiverse theories and show that these arguments do not justify arguing the scientific nature of such theories. Moreover, even if we accept the proposals of the epistemic shift and the nonempirical theory assessment, I argue that multiverse theories still cannot pass or satisfy the required assessments based on the new theoretical virtues and the nonempirical arguments. (shrink)

As a candidate theory of quantum gravity, the popularity of string theory has waxed and waned over the past four decades. One current source of scepticism is that the theory can be used to derive, depending upon the input geometrical assumptions that one makes, a vast range of different quantum field theories, giving rise to the so-called landscape problem. One apparent way to address the landscape problem is to posit the existence of a multiverse; this, however, has in turn drawn (...) heightened attention to questions regarding the empirical testability and predictivity of string theory. We argue first that the landscape problem relies on dubious assumptions and does not motivate a multiverse hypothesis. Nevertheless, we then show that the multiverse hypothesis is scientifically legitimate and could be coupled to string theory for other empirical reasons. Looking at various cosmological approaches, we offer an empirical criterion to assess the scientific status of multiverse hypotheses. (shrink)