Fankhauser Johannes, Read James
Institute for Theoretical Physics, University of Innsbruck, Austria.
Faculty of Philosophy, University of Oxford, UK.
Stud Hist Philos Sci. 2024 Dec;108:19-27. doi: 10.1016/j.shpsa.2024.09.001. Epub 2024 Oct 1.
Gravitational redshift effects undoubtedly exist; moreover, the experimental setups which confirm the existence of these effects-the most famous of which being the Pound-Rebka experiment-are extremely well-known. Nonetheless-and perhaps surprisingly-there remains a great deal of confusion in the literature regarding what these experiments really establish. Our goal in the present article is to clarify these issues, in three concrete ways. First, although (i) Brown and Read (2016) are correct to point out that, given their sensitivity, the outcomes of experimental setups such as the original Pound-Rebka configuration can be accounted for using solely the machinery of accelerating frames in special relativity (barring some subtleties due to the Rindler spacetime necessary to model the effects rigorously), nevertheless (ii) an explanation of the results of more sensitive gravitational redshift outcomes does in fact require more. Second, although typically this 'more' is understood as the invocation of spacetime curvature within the framework of general relativity, in light of the so-called 'geometric trinity' of gravitational theories, in fact curvature is not necessary to explain even these results. Thus (a) one can often explain the results of these experiments using only the resources of special relativity, and (b) even when one cannot, one need not invoke spacetime curvature. And third: while one might think that the absence of gravitational redshift effects would imply that spacetime is flat (indeed, Minkowskian), this can be called into question given the possibility of the cancelling of gravitational redshift effects by charge in the context of the Reissner-Nordström metric. This argument is shown to be valid and both attractive forces as well as redshift effects can be effectively shielded (and even be repulsive or blueshifted, respectively) in the charged setting. Thus, it is not the case that the absence of gravitational effects implies a Minkowskian spacetime setting.
引力红移效应无疑是存在的；此外，证实这些效应存在的实验装置——其中最著名的是庞德 - 雷布卡实验——广为人知。然而，或许令人惊讶的是，文献中对于这些实验究竟证实了什么仍存在大量混淆。我们在本文中的目标是以三种具体方式澄清这些问题。首先，虽然（i）布朗和里德（2016 年）正确地指出，鉴于其灵敏度，诸如原始庞德 - 雷布卡配置之类的实验装置的结果仅使用狭义相对论中加速参考系的机制就可以解释（不考虑由于严格模拟这些效应所需的林德勒时空而产生的一些微妙之处），但是（ii）对更灵敏的引力红移结果的解释实际上确实需要更多东西。其次，虽然通常这种“更多”被理解为在广义相对论框架内引入时空曲率，但鉴于引力理论的所谓“几何三位一体”，实际上即使解释这些结果也不一定需要曲率。因此（a）人们通常仅使用狭义相对论的资源就能解释这些实验的结果，并且（b）即使不能，也不必引入时空曲率。第三：虽然人们可能认为引力红移效应的不存在意味着时空是平坦的（实际上是闵可夫斯基时空），但考虑到在雷斯纳 - 诺德斯特龙度规的背景下电荷可能抵消引力红移效应，这一点可能会受到质疑。这个论点被证明是有效的，并且在带电情况下，吸引力和红移效应都可以被有效屏蔽（甚至分别表现为排斥力或蓝移）。因此，不存在引力效应并不意味着是闵可夫斯基时空背景。
