For this question, I don't want to explore what "space" is (quantum chaos or otherwise), or whether it has mass, etc. Instead, I just want to explore if it qualifies as a medium, like air or water. I have a line of reasoning I want to explore, but as it is based on "space" being considered a medium, I want to explore this hypothesis first. It would seem to me that is a medium. A couple of possible arguments in favor might be: - Light is a wave, and generally waves need to propagate in something - The current theory of red shift posits that light from distant galaxies increases in wavelength as it passes through the space between us. As the fabric of space expands, it stretches out the light waves passing through it. Does this imply that space qualifies as a medium?