Is the Mentaculus the Best System of Our World?

Barry Loewer and David Albert put forward a theory that they call ?The Mentaculus?, which they claim to be ?arguably a complete scientific theory of the universe?. Albert and Loewer?s Mentaculus is an expanded version of their version of statistical mechanics. On their view - as recently updated by Loewer?s ?Package Deal Approach? - The Mentaculus is the ?best system? of our world in the Lewis-style sense of this term: it contains a partial description of the fundamental reality (?The Humean base?) and provides the optimal balance between informativeness and simplicity. The Mentaculus has other advantages, in particular, it is reductionist in the sense that it unifies all the sciences, and it is physicalist in the sense that the account of everything is ultimately based on physics. In this paper we examine the extent to which The Mentaculus is reductionist and physicalist. We compare it with ?Flat Physicalism?, which is our version of expanded statistical mechanics, that is a reductive type-type physicalist identity theory of everything that there is. The Mentaculus is less reductionist than Flat Physicalism, since whereas both theories assume the fundamental microdynamics and suitable contingent facts, The Mentaculus assumes the Past Hypothesis and a Statistical Postulate, that Flat Physicalism derives from the microdynamics and the contingent facts. Additionally, Flat Physicalism derives from the latter all the special sciences kinds and laws, while The Mentaculus does not contain any explanatory account of such reduction. Therefore, Flat Physicalism is arguably ?better? than The Mentaculus in the ?best system? sense of the term.