Could the Hubble tension between the CMB (Hubble value of 67) and the supernova Hubble ladder (value of 73) be the emissivity of the universe given the detectors of the CMB are thermo-electric? Thermoelectric devices all produce bell-shaped curves called blackbody curves and they all have the emissivity correction problem.
If we assume the ladder method is correct and there is a systematic (emissivity) error in the CMB map, what temperature would the universe have to be to make the two have a Hubble constant equal to the ladder method? That difference, I think, would be the emissivity of the universe. And that would be an acceptable solution as all things have an emissivity reading, why not the universe?