Thermodynamics has a clear arrow of time, characterized by the irreversible approach to equilibrium. This stands in contrast to the laws of microscopic theories, which are invariant under time-reversal. Foundational discussions of this “problem of irreversibility” often focus on historical considerations, and do therefore not take results of modern physical research on this topic into account. In this article, I will close this gap by studying the implications of dynamical density functional theory (DDFT), a central method of modern nonequilibrium statistical mechanics not previously considered in philosophy of physics, for this debate. For this purpose, the philosophical discussion of irreversibility is structured into five problems, concerned with the source of irreversibility in thermodynamics, the definition of equilibrium and entropy, the justification of coarse-graining, the approach to equilibrium and the arrow of time. For each of these problems, it is shown that DDFT provides novel insights that are of importance for both physicists and philosophers of physics.

热力学有一个明确的时间箭头，其特点是不可逆地接近平衡。这与微观理论的定律形成对比，后者在时间反转下是不变的。对这个“不可逆性问题”的基础性讨论往往集中在历史考量上，因此没有考虑到现代物理学对此主题的研究结果。在本文中，我将通过研究动态密度泛函理论的含义来弥补这一差距（DDFT），一种现代非平衡统计力学的中心方法，以前没有在物理学哲学中考虑过，用于本次辩论。为此，关于不可逆性的哲学讨论分为五个问题，涉及热力学中不可逆性的来源、平衡和熵的定义、粗粒度的证明、平衡的方法和时间之箭。对于这些问题中的每一个，都表明 DDFT 提供了对物理学家和物理学哲学家都很重要的新颖见解。