From: guskz on
Curved instead of Euclidean space is considered during light's travel.
Gravity causes light to redshift.
Gravity warps, curves; thus shapes space.

Therefore if space is curved based on the total gravitational
potential then an equivalent redshift times distance, must be added to
calculations in addition to the redshift from space's expansion.

As well, the expansion potential is a non-Euclidean curved space; it
may be spherical or hyperbolic, and this shape may be positive or
negative in terms of how it affects light's wavelength shift.