The Symmetry of Time And The Branch Hypothesis

Abstract

Reichenbach’s posthumous book about time’s arrow is the first detailed treatment of the philosophically significant and intriguing aspect of time referred to in Eddington’s striking metaphor. The philosophical issues implicit in time’s arrow failed to interest an impressive group of leading philosophers of this century who made important contributions to the understanding of other aspects of time (Bergson, Broad, Carnap, Cassirer, Russell, Schlick, and Whitehead). Of course, the problem of the direction of time was too challenging to have been completely disregarded by Reichenbach’s contemporaries. Some of them explored the same issue without using Reichenbach’s terminology. Instead of referring to the direction of time or to time’s arrow, they discussed ‘temporal unidirectionality’ (Zilsel [1927], p. 280ff), ‘temporal anisotropy’ (Mehlberg [1935], p. 171ff), ‘temporal asymmetry’ (Smart [1954], p. 79ff), or the ‘flow of time’ (Margenau [1954], p. 79ff). It is remarkable, however, that an investigator of Reichenbach’s stature should have dealt with the single issue of time’s arrow in a substantial book full of surprising ideas and of some equally surprising misunderstandings.