 In the Coen brothers’ film, the character Arthur Gopnik, a mathematician, spends his days on a couch filling a notebook with a probability map of the universe, the Mentaculus. It is an apt name for what statistical mechanics provides us according to Albert and Loewer. In effect, it provides us with a probability map for every macroscopic generalization because it provides probabilities over all the microstates realizing these macrostates. The package is composed of the following elements: the past hypothesis (that the entropy of initial macrostate \(M(0)\) is extremely low), a uniform probability distribution over the microstates that realize \(M(0)\), the present macrostate \(M(t)\), and the dynamical laws of the microlevel.