Illumination and Construal: Light as Enabler and Constrainer of Possibility: 7 Electromagnetism and Modern Physics: Light as Relational Medium

By the nineteenth century, light was no longer only a phenomenon of myth, metaphor, or optics. It became the pivot around which a new relational physics emerged. James Clerk Maxwell’s equations unified electricity, magnetism, and light into a single field theory, showing that light was not a substance or particle to be contained, but a wave propagating through an all-encompassing field. Possibility here was no longer constrained by bodies and their collisions, but by the relational properties of fields that permeated and structured space.

Einstein’s relativity deepened this reconstrual. Light was no longer simply a wave in a field, but the very measure of space and time. The invariance of the speed of light established the relational frame in which all motion and all simultaneity must be construed. Space and time ceased to be absolutes; they were revealed as perspectival relations shaped by the luminous constant.

This shift marks a decisive stage in the genealogy of light as possibility: it is no longer only a vehicle of perception, nor only a medium of divine order, but the very architecture through which the cosmos can be related. Light conditions not only what can be seen, but what it means to inhabit a universe at all. The relational turn in physics — field, relativity, invariance — recasts possibility itself as structured through luminous relations.

In this movement, light becomes both the horizon and the measure: the field that binds, the constant that constrains, and the medium that opens the cosmos as a relational whole.