Hubble
Vesto Slipher first observed the shifts in spectral lines of light from galaxies in 1912. Slipher working at Lowell Observatory, Edwin Hubble at Mount Wilson Observatory and others soon established a rough proportionality of galactic distances to their redshifts.A common early interpretation of this redshift was that it was caused by the doppler shift of galaxies racing away from the earth. After the expanding Friedmann solution to general relativity was found, this interpretation changed to one where photons of light emitted by atoms long ago have expanded exactly like the Universe in the time they have been traveling to reach the earth. The further away the source, the more time both the Universe and photons of light have been expanding, and the redder photons have become.
To measure a color shift, astronomers must compare the color of photons from galaxies to the color of photons from atoms in today's laboratories. To say that Hubble redshift is caused by the redshift of photons, astronomers must assume that atoms long ago emitted exactly the same color of light that reference atoms do today.
Astronomers assume that the wavelengths of photons change exactly as Schrödinger calculated, but have ignored the equivalent evolution of atomic wave functions that Schrödinger's reasoning also requires. The evolution of both atoms and photons must be considered to correctly interpret Hubble redshift, since every quantum wave wavefunction changes with the spacetime geometry of the Universe, every one.
One immediate implication for cosmology of the evolution of atoms is that the meaning of Hubble redshift flips to imply that the Universe is contracting. This comes directly from comparing the wavelengths of new photons emitted by today's atoms against older photons. Atomic emissions have redshifted about twice as much as photons have since they were emitted long ago. Hubble blueshift is characteristic of expanding universes. Redshift is characteristic of contracting universes.
Edwin Hubble and Richard Tolman