International Astronomy and Astrophysics Research Journal

Aims: The propagation of light in vacuo has generally been assumed to be isotropic; i.e., its recessional velocity is assumed to be identical with its return speed back to the observer. This article presents a novel conceptual approach to this fundamental yet unresolved issue in physics: Is light propagation isotropic? The synchronization of mutually-distant time clocks has long been the bane of speed of light measurements. If such synchronization can be achieved at arbitrarily large or even astronomical scales, it can lay the foundation for methods to directly measure the one-way speed of light. Building upon this basis, any potential latent anisotropy which may be inherent in the propagation of light can then be investigated, both terrestrially and between the Earth and Moon or other planetary bodies.

Methodology: We propose methods whereby mutually distant (unsynchronized) atomic clocks are positioned on the Earth and the Moon. The clocks are devised to receive a set of signals transmitted from a man-made satellite or probe positioned at great mutual distance to the clocks and outside the ecliptic plane. The satellite emits electromagnetic timing signals (RF/laser); these signals serve as remote common external events to the atomic clocks. The clocks set themselves simultaneously to these signals, and are thereby synchronized by the same distantly-sourced external event(s).

Conclusion: Many novel and technically intricate speed of light measurement methodologies have been devised to measure, directly or indirectly, the speed of light between two points, with varying degrees of accuracy and reliability. However, none has yet shown promise to scale to astronomical distances. Practical experimental schemes are put forth herein for synchronizing mutually-distant atomic clocks. This allows for the direct measurement of the one-way speed of light, a feat which has never been accomplished definitively. Measurements of this nature could provide direct evidence to support or undermine the cosmological principle, with far-reaching ramifications.