Comment on superluminality in general relativity

TL;DR

This paper discusses how general relativity explains apparent superluminal effects due to gravitational time dilation, clarifying that such phenomena do not inherently imply true superluminal travel.

Contribution

It clarifies the distinction between apparent and intrinsic superluminality within the framework of general relativity, emphasizing the role of gravitational time dilation.

Findings

Average velocity over finite paths can differ from light speed due to gravitational effects

Superluminal appearance does not imply actual faster-than-light travel

Gravitational fields do not intrinsically cause superluminality

Abstract

General relativity provides an appropriate framework for addressing the issue of sub- or superluminality as an apparent effect. Even though a massless particle travels on the light cone, its average velocity over a finite path measured by different observers is not necessarily equal to the velocity of light, as a consequence of the time dilation or contraction in gravitational fields. This phenomenon occurs in either direction (increase or depletion) irrespectively of the details and strength of the gravitational interaction. Hence, it does not intrinsically guarantee superluminality, even when the gravitational field is reinforced.