Hi, newbie reading the forum with interest, and trying to understand how expansion manifests itself physically. Four possibilities; 1. New space is created between existing space, pushing galaxies apart 2. Existing space is stretched, pushing galaxies apart 3. Empty space is nothing, and galaxies are just thrown apart 4. Galaxies aren't physically moving apart (other than peculiar motion) #1 & 2 allow for FTL separation (if redshift sufficient) by manipulating space, rather than moving in space, but they imply empty space has some sort of physical structure, which I don't understand. #3 requires no structure for empty space, but implies FTL motion in space, which I don't understand. I'm assuming #4 is not compatible with accepted theory, therefore moot. What is this space "stuff" that is expanding? Reminds me of the aether. I'm told in GR curved spacetime is a mathematical treatment, not a physical reality; is expansion is the same? TIA.