Sean Gryb (University of Groningen): “Explaining time’s arrow: how scale symmetry affects notions of typicality in the universe”

Abstract: A persistent problem in the metaphysics of time is explaining the origin of the apparent arrow of time. Popular explanations rely on the ability to define a notion of typicality for the universe as a whole. We argue that such approaches face serious difficulties. Severe mathematical and epistemological obstacles need to be overcome before a precise proposal can even be stated. More importantly, the approach is obstructed by a new symmetry argument related to the scale independence in the universe. We explain how one of the oldest known dynamical symmetries has significant albeit vastly unappreciated consequences for defining notions of typicality in the universe. We then show how these considerations pose significant difficulties for standard approaches to explanations of the arrow of time and suggest a promising new way forward that has the potential to sidestep the more problematic aspects of the standard approach.