标题： 任何经典引力与量子物质之间一致的耦合本质上都是不可逆的。 显示英文标题

标题： Any consistent coupling between classical gravity and quantum matter is fundamentally irreversible

摘要： 当引力由一个量子系统源时，它作为基本相互作用的媒介（预计会获得非经典特征）和它在决定时空属性（本质上是经典的）中的角色之间存在矛盾。从根本上说，这种矛盾应该导致破坏量子理论或广义相对论的基本原则之一，但在没有诉诸特定模型的情况下通常很难评估是哪一个。在这里，我们使用广义概率理论（GPTs）以一种独立于理论的方式回答了这个问题。我们考虑引力场与单一物质系统之间的相互作用，并推导出一个不可能定理，表明当引力是经典的时候，至少需要违反以下假设之一：(i) 物质自由度由完全非经典的自由度描述；(ii) 物质自由度与引力场之间的相互作用是可逆的；(iii) 物质自由度会对引力场产生反作用。我们论证这表明经典引力和量子物质的理论必须在根本上是不可逆的，就像Oppenheim等人最近提出的模型一样。相反，如果我们要求量子物质与引力场之间的相互作用是可逆的，那么引力场必须是非经典的。 显示英文摘要

摘要： When gravity is sourced by a quantum system, there is tension between its role as the mediator of a fundamental interaction, which is expected to acquire nonclassical features, and its role in determining the properties of spacetime, which is inherently classical. Fundamentally, this tension should result in breaking one of the fundamental principles of quantum theory or general relativity, but it is usually hard to assess which one without resorting to a specific model. Here, we answer this question in a theory-independent way using General Probabilistic Theories (GPTs). We consider the interactions of the gravitational field with a single matter system, and derive a no-go theorem showing that when gravity is classical at least one of the following assumptions needs to be violated: (i) Matter degrees of freedom are described by fully non-classical degrees of freedom; (ii) Interactions between matter degrees of freedom and the gravitational field are reversible; (iii) Matter degrees of freedom back-react on the gravitational field. We argue that this implies that theories of classical gravity and quantum matter must be fundamentally irreversible, as is the case in the recent model of Oppenheim et al. Conversely if we require that the interaction between quantum matter and the gravitational field is reversible, then the gravitational field must be non-classical.