A Laboratory-Scale Foucault Pendulum for the Measurement of Frame-Dragging

A Foucault pendulum is generally considered to swing in a fixed orientation relative to the inertial frame of the fixed stars. However, according to general relativity, there is a small but finite precession over time of the pendulum swing plane relative to the fixed stars due entirely to the frame-dragging effect predicted by general relativity. This form of frame-dragging is represented physically by the Lense-Thirring precession of a gyroscopic test mass due to the proximity and the rotation of a massive body to the test mass. This precession may be calculated for various astrodynamic scenarios, but can also be modelled and calculated for a small test mass in the vicinity of the rotating planetary mass of the Earth. This manifestation of frame-dragging has already been measured in low Earth orbit (LEO) by the GP-B and LAGEOS missions, but it has not, to the authors’ knowledge, been measured terrestrially as yet. The work described in this chapter is leading to an attempt to make this measurement, using a short, instrumented, Foucault pendulum in the northerly latitude of Glasgow in Scotland. The chapter will summarize the work done to date to model the frame-dragging effect using the analogy of gravitoelectromagnetism and then will focus on the design and build of the Foucault pendulum, which will be used to attempt the measurement, and will end with a brief summary of the requirements of the measurement itself.