Abstract

The paper proposes a re-assessment of Reichenbach’s ‘causal’ theory of time. Reichenbach’s version of the theory, first proposed in 1921, is interesting because it is one of the first attempts to construct a causal theory as a relational theory of time, which fully takes the results of the Special theory of relativity into account. The theory derives its name from the cone structure of Minkowski space–time, in particular the emission of light signals. At first Reichenbach defines an ‘order’ of time, a ‘before-after’ relationship between mechanical events. In his later work, he comes to the conclusion that the ‘order’ of time needs to be distinguished from the ‘direction’ of time. He therefore abandons the sole focus on light geometry and turns to Boltzmann’s statistical version of thermodynamics. However, as Einstein pointed out, the emission and reception of light signals have thermodynamic aspects. When this is taken into account, Reichenbach’s ‘causal’ theory turns out to be an entropic theory of time. It also emerges that Reichenbach discusses phase space and typicality arguments in support of his dynamic view of time. They provide a better understanding of the notion of entropy. This unifies his approach and helps to answer some of the standard objections against a causal theory of time.