Constructor Theory of Thermodynamics Chiara Marletto1 Materials Department, University of Oxford July 2016 The laws of thermodynamics, powerful for countless purposes, are not exact: both their phenomenological and their statistical-mechanical versions are valid only at ‘macroscopic scales’, which are never defined. Here I propose a new, exact and scale-independent formulation of the first and second laws of thermodynamics, using the principles and tools of the recently proposed constructor theory. Specifically, I improve upon the axiomatic formulations of thermodynamics (Carathéodory, 1909; Lieb & Yngvason, 1999) by proposing an exact and more general formulation of ‘adiabatic accessibility’. This work provides an exact distinction between work and heat; it reveals an unexpected connection between information theory and the first law of thermodynamics (not just the second); it resolves the clash between the irreversibility of the ‘cycle’-based second law and time-reversal symmetric dynamical laws. It also achieves the long-sought unification of the axiomatic version of the second law with Kelvin’s. 1. Introduction An insidious gulf separates existing formulations of thermodynamics from other fundamental physical theories. Those formulations are approximate and scale-dependent – i.e., they have only a certain domain of applicability, or hold only at a certain ‘scale’, or level of ‘coarse-graining’, none of which are ever specified. So existing thermodynamics can provide powerful predictions and explanations of ‘macroscopic’ systems such as Victorian heat engines, but not 1 Address for correspondence:
[email protected] 1 about ‘microscopic’ ones, such as individual quantum systems. Consequently, the conventional wisdom is that thermodynamics is not a fundamental theory of physics at all.