Comments on the paper by S. Samuel "On the speed of gravity and the Jupiter/Quasar measurement"

TL;DR

This paper critiques Samuel's review on the speed of gravity, clarifying the correct relativistic principles of light propagation in gravitational fields and highlighting conceptual errors in Samuel's interpretation.

Contribution

It provides a clear, Lorentz-invariant derivation of the relativistic time delay and corrects misconceptions about the speed of gravity versus the speed of light.

Findings

Clarifies the correct relativistic time delay expression.

Identifies and explains errors in Samuel's theory.

Emphasizes the distinction between the speed of gravity and light.

Abstract

Recent review article by S. Samuel "On the speed of gravity and the Jupiter/Quasar measurement" published in the International Journal of Modern Physics D13, 1753 (2004) provides the reader with a misleading "theory" of the relativistic time delay in general theory of relativity. Furthermore, it misquotes original publications by Kopeikin and Fomalont & Kopeikin related to the measurement of the speed of gravity by VLBI. We summarize the general relativistic principles of the Lorentz-invariant theory of propagation of light in time-dependent gravitational field, derive Lorentz-invariant expression for the relativistic time delay, and finally explain why Samuel's "theory" is conceptually incorrect and confuses the speed of gravity with the speed of light.