Robert W. Batterman's monograph in the philosophy of physics focuses on how the Fluctuation-Dissipation theorem reveals important consequences for exploring and understanding the behavior of large, many-body systems. He develops a powerful methodology that privileges mesoscale levels between theories describing everyday behaviors of fluids and bending beams and those theories that describe the more fundamental, atomic nature of materials. The "hydrodynamic approach," which has its origins in Einstein's work on Brownian motion, aims to describe and account for continuum behaviors by largely ignoring details at the "fundamental" level. Einstein's work led to a fundamental theorem of statistical mechanics called the "Fluctuation-Dissipation" theorem. He argues against reductionist attempts to derive directly upper level theories from fundamental theories. Instead, he presents an approach to inter-theory relations that starts in the middle, bridging up to theories describing large scale behavior and down to those describing fundamental features.
