Measured speed versus true speed

TL;DR

This paper compares theoretical predictions and experimental thought experiments regarding the one-way and two-way speeds of light, suggesting only one inertial frame has an isotropic one-way light speed and exploring how to determine true speeds.

Contribution

It demonstrates, through a gedanken experiment, that the one-way speed of light can vary with frame velocity, challenging the assumption of isotropy in all inertial frames.

Findings

Two-way speed of light is constant across inertial frames.

Only one inertial frame has an isotropic one-way light speed.

Method to determine true speeds of entities and frames is proposed.

Abstract

The theoretical predictions, derived from the Lorentz and the Tangherlini transformations, for the one-way speed of any physical entity are confronted with the corresponding expressions for the one-way measured speed obtained from a gedanken experiment. The experiment demonstrates that, for an inertial frame $K'$ in motion relative to an inertial frame $K$ where the one-way speed of light is isotropic, even the special theory of relativity renders the one-way speed of light as function of the velocity of $K'$ in agreement with the Tangherlini transformations. However, the two-way speed of light remains constant for all inertial frames, in agreement with the two-way experimental techniques. This implies that there must exist \emph{one and only one} inertial frame where the one-way speed of light is isotropic. These investigations also show how we can determine, with certain restrictions, the true speed of a physical entity and of the true speed of $K'$ relative to $K$.