Brown and Janssen on the Arrow of Explanation in Special Relativity

I examine the debate between Michel Janssen and Harvey Brown over the arrow of explanation in special relativity. Brown argues that the symmetries of the dynamical laws explain the symmetries of space-time, whereas Janssen argues for the converse. Janssen has recently argued against Brown’s position on the grounds that it recommends trying to infer information from the relativistic effects, e.g., length contraction, in a way wasteful of time and resources. I show how Brown can respond to Janssen and trace the dispute not to a methodological difference, but to opposing positions on the meaning of spatio-temporal symmetries. According to Janssen, the symmetries of space-time are constraints on dynamical laws. According to Brown, symmetries of space-time arise jointly from matter distributions and the laws governing matter. Finally, I provide some considerations in favor of Brown’s position.