Time’s Arrow, Time’s Fly-Bottle

Abstract

For more than a century, physics has known of a puzzling conflict between the time asymmetry of thermodynamic phenomena and the time symmetry of the underlying microphysics on which these phenomena depend. In this talk I offer an introduction to the current status of this puzzle, distinguishing the central issue from various pseudo-issues with which it may be confused. In particular, I point out that there are two competing conceptions of what is needed to resolve the puzzle of the thermodynamic asymmetry, which differ with respect to the number of distinct time-asymmetries they take to be manifest in the physical world. On the preferable one-asymmetry conception, the remaining puzzle concerns the ordered distribution of matter in the early universe. The puzzle of the thermodynamic arrow thus becomes a puzzle for cosmology.