The three-fold theoretical basis of the Gravity Probe B gyro precession calculation

TL;DR

This paper discusses the theoretical foundations of the Gravity Probe B gyroscope precession predictions, emphasizing three key elements of gravity theory that are well-supported by prior experiments and theory.

Contribution

It clarifies and validates the three fundamental theoretical assumptions underlying the GP-B precession predictions, strengthening confidence in general relativity.

Findings

GP-B results agree with GR predictions within experimental errors

Each of the three theoretical elements is well-supported by previous experiments

The agreement enhances confidence in applying GR to astrophysics

Abstract

The Gravity Probe B (GP-B) experiment is complete and the results are in agreement with the predictions of general relativity (GR) for both the geodetic precession, 6.6 arcsec/yr to about 0.3%, and the Lense-Thirring precession, 39 marcsec to about 19%. This note is concerned with the theoretical basis for the predictions. The predictions depend on three elements of gravity theory, firstly that macroscopic gravity is described by a metric theory such as general relativity, secondly that the Lense-Thirring metric provides an approximate description of the gravitational field of the spinning earth, and thirdly that the spin axis of a gyroscope is parallel displaced in spacetime, which gives its equation of motion. We look at each of these three elements to show how each is solidly based on previous experiments and well-tested theory. The agreement of GP-B with theory strengthens our belief that all three elements are correct and increases our confidence in applying GR to astrophysical phenomena. Conversely, if GP-B had not verified the predictions a major theoretical quandary would have occurred.