The rate at which the universe is expanding, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the cosmos. However, a persistent difference called the "Hubble Tension" is seen between the value of the constant measured with a wide range of independent distance indicators and its value predicted from the big bang afterglow.
It confirms the redshift, but scientists have no way of knowing that it’s caused by the doppler effect, they just assume it is.
Rather, the standard model is not fully understood and light redshifts naturally over great distances due to losing energy to gravity waves, but that implies photons have mass which violates the standard model.
Maybe im crazy, but i think it’s a lot more likely the standard model is not correct with regard to photon mass as opposed to there’s an exotic force that violates conservation of mass/energy. I suppose either is quite incredible. I just refuse to assume the universe is accelarating expansion for seemingly no reason. And if photons are affected by gravitational fields, it makes perfect sense they have some reactive effect on gravity as well.