 The book makes a number of important and original contributions. It contains a detailed investigation into the philosophical foundations of statistical mechanics, especially examining the status of the second law of thermodynamics, which states that the entropy of a closed system can increase, but never decrease. Reichenbach explored connections between statistical mechanics and the new field of information theory—Shannon and Weaver’s classic book (1949) on the topic had been published just a few years earlier. In addition to the asymmetry of entropy increase described by the second law of thermodynamics, the book examined other temporally asymmetric phenomena. One of these was the asymmetry of records: We have detailed records of past events, including human memories and human made documents such as records and history books, but also including natural phenomena such as fossils, tree rings, and geological strata. These records provide us with a rich source of information about the past. We have no comparable source of information about the future, although we can reliably predict certain events, such as solar eclipses.