The most recent attempt at factually establishing a "true" value for the one-way velocity of light is shown to be faulty. The proposal consists of two round-trip photons travelling first in vacuo and then through a medium of refractive index n before returning to their common point of origin. It is shown that this proposal, as well as a similar one considered by Salmon (1977), presupposes that the one-way velocities of light are equal to the round-trip value. Furthermore, experiments of (...) this type, involving regions of space with varying refractive indices, cannot "single out" any factual value for the Reichenbach-Grünbaum ε factor thus posing no threat to the conventionalist thesis. (shrink)

I defend the opinion that Cavalleri and Spinelli, who in the last years abandoned many of the relativity dogmas and embraced many of the absolute conceptions, are still very far from an adequte understanding and interpretation of physical reality.

Two recently proposed experiments by Kolen and Torr (K-T), designed to detect possible failures of Einstein's special relativity (SR) are analyzed. Imprecisions in these papers are pointed out. Computation in Lorentz aether theory (LAT), with the K-T violation of SR, of the theoretical prediction for the proposed K-T clock experiment prove their results to be incorrect. Analytical computation of the proposed K-T rotor Doppler experiment using LAT confirms the order of magnitude of their prediction by numerical computation. For LAT in (...) the K-T form, this experiment, using a turntable, is shown to give results which could be detected with the technology of 20 years ago. Another LAT model is considered which leads to deviations of SR smaller than in the K-T model. The central point of the approach adopted in this paper is the use of Einstein's coordinates in the comoving frame, even when SR is violated, leading always to isotropic propagation of light in vacuum; the anisotropy usually obtained in LAT is only a coordinate effect. (shrink)

The claim that distant simultaneity with respect to an inertial observer is conventional arose in the context of a space-and-time rather than a spacetime ontology. Reformulating this problem in terms of a spacetime ontology merely trivializes it. In the context of flat space, flat time, and a linear inertial structure (a purely space-and-time formalism), we prove that the hyperplanes of space for a given inertial observer are determined by a purely spatial criterion that depends for its validity only on the (...) two-way light principle, which is universally regarded as empirically verified. All (empirically determined) “spacetime” entities, such as the conformal structure or light surface equation, are used in a purely mathematical manner that is independent of and hence isneutral with respect to the ontological status that is ascribed to them. In this regard, our criterion is significantly stronger than thespacetime criterion recently advanced by D. Malament, which appeals explicitly to the conformal orthogonality of spacetime vectors and to the invariance of the conformal-orthogonal structure of spacetime under the causal automorphisms of spacetime. Once the hyperplanes of space for a given inertial observer have been determined by our empirical and purely spatial criterion, the following holds: there exists one and only one $\vec \varepsilon $ -synchronization procedure, namely the standard procedure proposed by Einstein, such that the planes of common time are thesame as the nonconventional hyperplanes of space for the inertial observer. It follows that our criterion provides an empirical even if indirect method for determining that the one-way speed of light is the same as the average two-way speed of light. In addition, two inertial observers that are not at rest with respect to each other necessarily havedifferent hyperplanes of space, and consequently their respective spatial views cannot be encompassed in a single three-dimensional space. Hence, our purely spatial criterion provides an empirical motivation for adopting the more comprehensive spacetime ontology. (shrink)