Thanks for the nice explanation! But another question: since the expansion rate of the universe has been different at different times, does this mean that the measured speed of light would be different at different times as well?<p>Because if the ruler you are using to measure is expanding at  rate x, the measured speed of light would be different than when the ruler is expanding at rate y?<p>So, during the deflationary period of the universe, the speed of light would be significantly smaller, correct? In fact, would it be &quot;negative&quot; due to the universe expanding faster than light?