发表机构
Harvard University（哈佛大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文将全息量子电路模型中与外部非引力系统纠缠的闭合宇宙子系统（第二类观测者模型）统一到微分同胚自发破缺对应的戈德斯通玻色子模型（第三类），指出观测者涌现是大质量岛范式的体现，引力子质量是量子态特征，且观测者可观测量子引力整体对称性。
AI 中文摘要
已有观点认为，在量子引力中，与任何闭合宇宙相关的希尔伯特空间是平凡的一维空间。为了协调这一观点与我们所处宇宙的丰富性，有学者提出，一旦纳入“观测者”，非平凡的希尔伯特空间就会涌现。这类“观测者”已通过多种方式建模，具体分为三类模型：1）将“观测者”建模为系统全哈密顿量中与相空间变量线性相关的项；2）在全息术的量子电路模型中，将“观测者”建模为闭合宇宙中与外部非引力系统纠缠的子系统；3）认为“观测者”由微分同胚自发破缺时涌现的戈德斯通玻色子描述。实际上，第三类模型是在尝试物理实现第一类模型时发现的。本文中，我们将证明第二类模型也可统一到第三类模型中。我们的结果表明，“观测者”的涌现是“大质量岛（Massive Islands）”范式的一种体现，它证明了引力子质量是量子态的一个特征。应将这些岛视为闭合宇宙，而与引力子质量相关的戈德斯通玻色子即为“观测者”，蒸发黑洞在后期的情况正是如此。本研究的一个推论是，“观测者”能够“观测”量子引力中的整体对称性。
英文摘要
It has been argued that in quantum gravity the Hilbert space associated with any closed universe is trivially one-dimensional. To reconcile this argument with the richness of our own universe, it was suggested that a nontrivial Hilbert space will emerge once an ``observer" is included. Such an ``observer" has been modeled in different ways. There are three concrete classes of models: $\textbf{1)}$ The ``observer" is modeled by a term in the full Hamiltonian of the system which is linear in a phase space variable; $\textbf{2)}$ The ``observer" is modeled in the quantum circuit model of holography as a subsystem in the closed universe which is entangled with an external non-gravitational system; $\textbf{3)}$ The ``observer" is argued to be described by the emergent Goldstone bosons when the diffeomorphisms are spontaneously broken. In fact, the third class was discovered by an attempt to physically realize the first class. In this paper, we will show that the second class can also be unified into the third class. Our result indicates that the emergence of the ``observer" is a manifestation of the $\textit{Massive Islands}$ paradigm. It demonstrates that the graviton mass is a feature of the quantum state. One should think of the islands as closed universes and the Goldstone boson associated with the graviton mass as the ``observer", which is exactly the case at late-times for evaporating black holes. An implication of this work is that the ``observer" can ``observe" global symmetries in quantum gravity.
Comments43 pages, 10 figures
