> that process just changes the frequency of photons, but not their density in space.
Frequency is precisely the necessary thing that needs to be considered as an observed phenomenon that can have alternative explanations, since frequency relates to shifting toward red.
Are you saying that density/luminosity is an independent way of corroborating universal expansion? I don't believe that's the case.
Neither luminosity nor redshift seem, IMHO, to be strong enough evidence to uphold a "preposterous" (to use Sean Carroll's favorite descriptive term for the world) theory that massive things are not just traveling but accelerating away from oneanother.
Frequency is precisely the necessary thing that needs to be considered as an observed phenomenon that can have alternative explanations, since frequency relates to shifting toward red.
Are you saying that density/luminosity is an independent way of corroborating universal expansion? I don't believe that's the case.
Neither luminosity nor redshift seem, IMHO, to be strong enough evidence to uphold a "preposterous" (to use Sean Carroll's favorite descriptive term for the world) theory that massive things are not just traveling but accelerating away from oneanother.