| The fundamental plasma processes of magnetic reconnection, turbulence, and collisionless shocks underlie a staggering array of processes in heliospheric, planetary, and astrophysical systems—such as the driver of eruptions at the sun, stars, and compact objects and the interaction of magnetospheres with ambient solar and stellar winds. In each process, energy in the form of bulk kinetic energy or magnetic fields is injected or stored at large length scales, and the energy is efficiently converted at small scales into other forms of energy including heat. How this energy is converted in strongly collisional systems is relatively well understood. However, energy conversion processes in weakly collisional or fully collisionless systems that can be far from thermodynamic equilibrium are only understood using expansion techniques, so these remain at the forefront of modern research on these topics. In this talk, I will discuss a suite of new results. First, we argue that the first law of thermodynamics, often used to study small-scale energy conversion, is fundamentally incomplete for weakly collisional and collisionless systems that are not in equilibrium. Then, we present a first-principles theory using the concept of entropy in kinetic theory that accounts for all energy conversion, even for systems arbitrarily far from thermodynamic equilibrium—we call this the “first law of kinetic theory” as it supplants the first law of thermodynamics for systems out of equilibrium. As a proof of principle, we calculate the new terms in state-of-the-art particle-in-cell simulations of magnetic reconnection. Numerical results and their implications will be summarized, and a host of potential applications of the theory will be discussed. |