Review on the minimally extended varying speed of light model

TL;DR

This paper reviews the concept of varying speed of light models within an expanding universe, discussing theoretical foundations, observational distinctions, and the implications of cosmic expansion on dimensional constants.

Contribution

It provides a comprehensive overview of minimally extended varying speed of light models and explores conditions under which the speed of light may vary over cosmic time.

Findings

Varying speed of light models depend on cosmic expansion context

Observational methods can potentially distinguish constant vs. varying c

Dimensional constants' variation is meaningful in an expanding universe

Abstract

It has been known that dimensional constants such as $\hbar$, $c$, $G$, $e$, and $k$ are merely human constructs whose values and units vary depending on the chosen system of measurement. Therefore, the time variation of dimensional constants lacks operational significance due to their dependence on them. It is well-structured and represents a valid discussion. However, this fact only becomes a meaningful debate within the context of a static or present universe. As well-established theoretically and observationally, the current universe is undergoing accelerated expansion, wherein dimensional quantities, like the wavelength of light, also experience redshift phenomena elongating over cosmic time. In other words, in an expanding universe, dimensional quantities of physical parameters vary with cosmic time. From this perspective, there exists the possibility that dimensional constants, such as the speed of light, could vary with the expansion of the universe. In this review paper, we contemplate under what circumstances the speed of light may change or remain constant over cosmic time, and discuss the potential for distinguishing these cases observationally.