The "displacement current in the medium" that Maxwell originally included in his equations was directly tied to his concept of the "luminiferous ether" as the medium through which light and electromagnetic waves propagated.
The ether was never definitively proven not to exist; however, extensive experiments, including those in space, have consistently failed to detect its presence. Notably, frame-dragging effects observed in experiments such as Gravity Probe B support the predictions of general relativity without requiring an ether.
The ether was never definitively proven not to exist; however, extensive experiments, including those in space, have consistently failed to detect its presence. Notably, frame-dragging effects observed in experiments such as Gravity Probe B support the predictions of general relativity without requiring an ether.
Very sad.