[deleted]
Tom,
In that pop physics book, it made the point that light doesn't register time because it has no internal action, thus no clock. If it did, then it would combine with velocity to exceed c. On the other hand, for those of us not traveling at c, it makes a very good yardstick of inter-stellar and inter-galactic distances. As you say, space and time are not physically independent, so why, if space is expanding, doesn't the propagation rate, time, increase as well?
As Peter points out, in various mediums, light moves slower than in a pure vacuum, but so does the clock. Why then, if the medium is expanding, wouldn't the "clock" also increase, so that it still records the same rate of propagation, relative to the dimensionality of the medium? You say the spatial dimensionality is stretched, but you use a non-stretched temporal yardstick to measure it against. It seem you are trying to separate time and space, by saying the spatial frame can grow, while the temporal yardstick remains constant.