Cosmic Ladder distance measurements establish the linearity of Hubble's law out to a distance of about 13 bly. However, even with mitigating facts, beyond 13 bly we do not know if the Hubble law line rate increases or decreases beyond its linear line rate, to thereby know if the universe accelerates or decelerates its expansion.

The Big Bang theory is an ad hoc theory based on complex mathematics of General Relativity, a theoretical model of an explosion of matter creating the Cosmic Microwave Background (CMB), and its use of actual CMB measurements to find Hubble's law theoretically. Beyond 13 bly we do not know if the Big Bang age of the universe is the real age and we do not know if the expansion is non-linear. The question arises why use the Big Bang theory when when all it does, even with many questionable assumptions, result in almost identical to actual measurements made by the Cosmic Ladder Microwave Background.