The Analysis of a Proposed Experiment to Measure the Speed of Gravity in Short Distances

TL;DR

This paper proposes two experiments using vibrating masses and sapphire detectors to measure the speed of gravity at short distances, with detailed analysis of detector design and sensitivity.

Contribution

It introduces a new sapphire detector shape and provides a high-precision analysis of experimental setups for measuring gravity's speed.

Findings

Both setups show similar sensitivity levels.

The vibrating mass experiment is more frequency-stable.

Achieved a signal-noise ratio of 10 at 5000 Hz.

Abstract

In order to investigate the speed of gravitational signals travelling in air or through a different medium two experiments were designed. One of the experiments contains 2 masses rotating at very high speed and in the other experiment a sapphire bar will vibrate, in both cases they will emit a periodic tidal gravitational signal and one sapphire device that behaves as a detector, which are suspended in vacuum and cooled down to 4.2 K will act as a detector. The vibrational amplitude of the sapphire detector device is measured by an microwave signal with ultralow phase-noise that uses resonance in the whispering gallery modes inside the detector device. Sapphire has a quite high mechanical Q and electrical Q which implies a very narrow detection band thus reducing the detection sensitivity. A new detector shape for the detector device is presented in this work, yielding a detection band of about half of the device vibrational frequency. With the aid of a Finite Element Program the normal mode frequencies of the detector can be calculated with high precision. The results show a similar expected sensitivity between the two experimental setup, but the experiment with the vibration masses is more stable in frequency then it is chosen for the experimental setup to measure the speed of gravity in short distances. Then a more precise analysis is made with this experiment reaching a signal-noise ratio of 10 at a frequency of 5000 Hz.