New phenomenology in the first-order thermodynamics of scalar-tensor gravity for Bianchi universes

The phase space of Bianchi I universes in vacuum Brans-Dicke gravity is analyzed in terms of physical variables. The behaviour of the solutions of the field equations near the fixed points (which are solutions of Einstein gravity) is compared with basic ideas of the recent first-order thermodynamics of scalar-tensor gravity, elucidating new phenomenology.