1 meter is defined as the distance travelled by light in 1 / 299,792,458 seconds. Doesn't this mean that "light slowing down" would be indistinguishable from "space expanding"?
Continuous Intrgration for the universe. Interesting.
Well it doesn't really tell whether it's changed from a moment ago. Rather whether it was much faster when the cosmic microwave background radiation was emitted, almost at the beginning of the Universe.