The aim of this work is to continue the exploration into the foundational questions on the physical theory that underpins our general theory of thermodynamics and that, for the first time, introduced probabilistic considerations into the fundamentals of our physical description of the world. That physical theory is statistical mechanics.

The history of this foundational quest is a long one. It begins with an intense examination of the premises of the theory at the hands of James Clerk Maxwell, Ludwig Boltzmann, and their brilliant critics. It continues in the work of Hans Reichenbach, who introduced their deep questions to the philosophical community. And the quest has persisted as a set of difficult conceptual challenges, in a study made ever richer by the development of ever more sophisticated technical resources with which to treat the problems. I hope that this book will encourage others in the philosophical community to join with those in physics who continue to look for the elusive resolutions of the puzzles.

I have benefited enormously from discussions with John Earman, who has often guided me to the crucial questions to be addressed. James Joyce and Robert Batterman, as students and as colleagues, have been enormously helpful to me in my thinking about these issues.