It is an observational fact that the arrow defined by the increase of thermodynamic entropy points in the same direction as the arrow defined by the expansion of the universe. However, the status of this relation is a highly debated issue. Famously, Gold (1958, 1962) argued that, far from being a contingent fact, the relation is a causal one: the thermodynamic entropy increases as a result of the expansion of the universe, whereas in a collapsing universe the entropy necessarily decreases.