Travelling light

Abstract

This paper draws arresting conclusions from its analysis of a distinctive, and to the best of my knowledge novel, kinematic construction–an infinite set of inertial coordinate systems that is indexed by a continuous real parameter. It explains how the description of the straight-line trip of a light pulse varies among the members of this infinite set, and also–very importantly–how in my view the trip can be described without referring it to any inertial coordinate system, using coordinate-system-independent kinematic concepts that are implicit in the structure of travelling light. This multitude of comparisons brings out certain features of Einstein’s special theory of relativity that are not apparent when kinematic thought is confined to comparing the analytic perspectives of two inertial coordinate systems, as is the custom. It shows that there are reasonable alternatives to the definitions of length, duration, and velocity used by Einstein. It shows that the velocity of light, defined in Einstein’s way, varies parabolically over the infinite set of inertial coordinate systems. It provides an attractive coordinate-system-independent explanation of the behaviour of light in Sagnac and modified Sagnac experiments. It elaborates and validates my belief that inertial coordinate systems are commonly misused in a variety of ways. By avoiding these misuses of inertial coordinate systems, physicists can think in less artificial, less arbitrary, more faithful-to-nature ways.