Is the phase of plane waves an invariant?

TL;DR

This paper questions the invariance of the phase of plane waves, especially in media with superluminal motion, and critiques recent radical proposals that challenge conventional understanding.

Contribution

It critically examines recent claims about plane wave phase invariance and highlights flaws, maintaining the traditional view of phase invariance as questionable.

Findings

Invariance of plane wave phase is questionable in superluminal media.

Recent radical proposals to modify plane wave concepts contain flaws.

The traditional concept of plane wave phase invariance remains under scrutiny.

Abstract

Based on the invariance of the phase of waves, plane waves was shown to propagate with negative frequencies in a medium which moves at superluminal speeds opposite to the propagation direction of plane waves. The validity of the invariance of the phase of plane waves was then called into question. A radical change of the conventional concept of plane waves is recently proposed to solve the problem of negative frequency of waves. Here, we point out flaws in that proposal. Thus, the validity of the invariance of the phase of plane waves remains questionable.