This is very speculative and involves many "ifs" but if cold radiation exists a crude explanation of cosmological redshift becomes possible. This requires reviving the caloric theory of heat but this time by complementing it with a frigoric "fluid". If radiation exchange between bodies of different temperature consists of caloric and frigoric "flows", then a counterflow heat exchanger model could explain how cosmological redshift arises. Distant stars would be at the hot end and observers on the Earth would be at the cool end. The cool end would reduce the energy (stretch the wavelength) of the incoming radiation.
Steve Mold explains how a counterflow heat exchanger works: https://www.youtube.com/watch?v=NvkZaWLe0Sk (An interesting aside: when Herschel discovered infrared radiation in 1800 he interpreted it as evidence of the caloric theory.) Harry
