标题： 事件的相对性：JT引力和线性化GR中的例子 显示英文标题

标题： Relativity of the event: examples in JT gravity and linearized GR

摘要： 量子引力中的可观测量以著名的方式渐近定义，即在AdS或闵可夫斯基空间的边界上。然而，通过固定一个坐标系或适当地为场算符着装，也可以采用一种近似的“准局域”方法，这种方法可以描述生活在时空内部的一组观测者所执行的测量。特别是，可以将空间坐标附加到这些观测者的时空中，并使用它们的固有时间作为时间坐标。在这里，我们强调任何这种局部表述都必须面对事件的相对性，因为改变参考系（=一组观测者）意味着事件点的重新分配以及它们如何被识别。因此，在量子引力中，不同参考系之间的坐标变换变得概率化。我们在Jackiw-Teitelboim引力中给出了这种机制的具体实现，其中可以通过与边界锚定的测地线来操作性地定义体内的一个点。我们描述了不同的实现方式，每种方式对应于不同的参考系，并计算了某些参考系之间变换的方差。特别是，我们计算了黑洞视界的定位方差，它在大多数参考系中似乎被弥散化了。然后，我们建议如何在爱因斯坦引力中计算这种效应，假设我们知道度规的波函数。这个想法是在一个半经典态的基础上展开后者，该基础中的每个元素具有标准/确定的坐标变换，结果通过叠加获得。作为一种娱乐性的探索，我们在闵可夫斯基时空中加入引力波的量子叠加，破坏了熟悉的洛伦兹boost，并计算了线性引力中向boosted参考系的概率变换。最后，我们尝试用着装算符的语言来表达事件的相对性。 显示英文摘要

摘要： Observables in quantum gravity are famously defined asymptotically, at the boundary of AdS or Minkowski spaces. However, by gauge fixing a coordinate system or suitably dressing the field operators, an approximate, "quasi-local" approach is also possible, that can give account of the measurements performed by a set of observers living inside the spacetime. In particular, one can attach spatial coordinates to the worldlines of these observers and use their proper times as a time coordinate. Here we highlight that any such local formulation has to face the relativity of the event, in that changing frame (= set of observers) implies a reshuffling of the point-events and the way they are identified. As a consequence, coordinate transformations between different frames become probabilistic in quantum gravity. We give a concrete realization of this mechanism in Jackiw-Teitelboim gravity, where a point in the bulk can be defined operationally with geodesics anchored to the boundary. We describe different ways to do so, each corresponding to a different frame, and compute the variances of the transformations relating some of these frames. In particular, we compute the variance of the location of the black hole horizon, which appears smeared in most frames. We then suggest how to calculate this effect in Einstein gravity, assuming knowledge of the wavefunction of the metric. The idea is to expand the latter on a basis of semiclassical states. Each element of this basis enjoys standard/deterministic coordinate transformations and the result is thus obtained by superposition. As a divertissement, we sabotage the familiar Lorentz boosts by adding to Minkoswki spacetime a quantum superposition of gravitational waves and compute the probabilistic transformation to a boosted frame in linearized gravity. Finally, we attempt to translate the relativity of the event in the language of dressed operators.