Background independence is often emphasized as an important property of a quantum theory of gravity that takes seriously the geometrical nature of general relativity. In a background-independent formulation, quantum gravity should determine not only the dynamics of space–time but also its geometry, which may have equally important implications for claims of potential physical observations. One of the leading candidates for background-independent quantum gravity is loop quantum gravity. By combining and interpreting several recent results, it is shown here how the canonical nature of this theory makes it possible to perform a complete space–time analysis in various models that have been proposed in this setting. In spite of the background-independent starting point, all these models turned out to be non-geometrical and even inconsistent to varying degrees, unless strong modifications of Riemannian geometry are taken into account. This outcome leads to several implications for potential observations as well as lessons for other background-independent approaches.

中文翻译：

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与背景无关的量子引力理论中的时空物理

背景独立性经常被强调为量子引力理论的一个重要特性，它认真对待广义相对论的几何性质。在与背景无关的公式中，量子引力不仅应确定时空动力学，还应确定其几何形状，这可能对潜在物理观测的主张具有同样重要的影响。与背景无关的量子引力的主要候选者之一是环量子引力。通过结合和解释最近的几个结果，这里展示了该理论的规范性质如何使在此设置中提出的各种模型中执行完整的时空分析成为可能。尽管起点与背景无关，所有这些模型都被证明是非几何的，甚至在不同程度上不一致，除非考虑到黎曼几何的强烈修改。这一结果对潜在的观察结果以及其他独立于背景的方法的经验教训产生了若干影响。