2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/125282In their recent paper [Phys. Rev. Lett. 98, 094101 (2007)], A. Porporato et al. studied the irreversibility and fluctuation theorem for stationary time series. In this comment, we point out that the fluctuation theorem is in fact the trivial outcome of a symmetry operation, and hence its physical contect is less convincing.1 pageStatistical Mechanicstext