Old and new ether-drift experiments: a sharp test for a preferred frame

TL;DR

This paper re-analyzes classical and modern ether-drift experiments, suggesting small deviations may indicate a preferred frame, and proposes a new test involving dielectric media to confirm or refute this hypothesis.

Contribution

It introduces a sharp experimental test using dielectric gases in resonant cavities to definitively confirm or exclude the existence of a preferred frame.

Findings

Classical experiments show small deviations consistent with a preferred frame.

Modern experiments with cavity-stabilized lasers are also consistent with a preferred frame when considering vacuum properties.

Replacing vacuum with a dielectric gas should amplify the observed frequency shifts if a preferred frame exists.

Abstract

Motivated by the critical remarks of several authors, we have re-analyzed the classical ether-drift experiments with the conclusion that the small observed deviations should not be neglected. In fact, within the framework of Lorentzian Relativity, they might indicate the existence of a preferred frame relatively to which the Earth is moving with a velocity v_earth\sim 200$ km/s (value projected in the plane of the interferometer). We have checked this idea by comparing with the modern ether-drift experiments, those where the observation of the fringe shifts is replaced by the difference \Delta \nu in the relative frequencies of two cavity-stabilized lasers, upon local rotations of the apparatus or under the Earth's rotation. It turns out that, even in this case, the most recent data are consistent with the same value of the Earth's velocity, once the vacuum within the cavities is considered a physical medium whose refractive index is fixed by General Relativity. We thus propose a sharp experimental test that can definitely resolve the issue. If the small deviations observed in the classical ether-drift experiments were not mere instrumental artifacts, by replacing the high vacuum in the resonating cavities with a dielectric gaseous medium (e.g. air), the typical measured \Delta\nu\sim 1 Hz should increase by orders of magnitude. This expectation is consistent with the characteristic modulation of a few kHz observed in the original experiment with He-Ne masers. However, if such enhancement would not be confirmed by new and more precise data, the existence of a preferred frame can be definitely ruled out.