In a paper published in Reviews of Modern Physics in 1949, http://journals.aps.org/rmp/pdf/10.1103/RevModPhys.21.378 , H.P. Robertson provided an analysis of the physical implications of the Michelson/Morley, Kennedy and Thorndike, and Ives and Stilwell experiments which seems definitive with respect to the points he sought to address. But, in his conclusion, he wrote something that, to some degree, is puzzling, or in some sense, seems unexpectedly incomplete. He writes: [T]he three second-order optical experiments of Michelson and Morley, of Kennedy and Thorndike, and of Ives and Stilwell, furnished empirical evidence which, within the limits of the inductive method, enables us to conclude that the three parameters (g0, g1, g2), may be taken as independent of the motion of the observer. The kinematics im kleinen of physical space-time is thus found to be governed by the Minkowski metric, whose motions are the Lorentz transformations, the background upon which the special theory of relativity and its later extension to the general theory are based. My first question is, what exactly did he intend to mean when he used the term "im kleinen" (trans: "in the small", or "in small scale"), and why did he stop there and not demonstrate that the Minkowski metric governs the kinematics, "im grossen" of space-time? Second, setting aside general relativistic and other "field" effects, does it mean that Robertson conceived that it was possible that space-time on a large scale might not be governed by the Minkowski metric? Why would/wouldnt he have been able to resolve the question at that time? To what extent has this question been addressed or resolved experimentally since Robertson's paper?