years). Redshift can be thought of as a series of transformations in photon wavelengths
between an infinite succession of closely-separated observers, resulting in an overall wavelength shift between two
observers with a finite separation and therefore an associated “velocity”. The second level of sophistication is
to ask what this velocity actually represents. [105] calculates the ratio of photon wavelength shifts between
pairs of fundamental observers to the shifts in their proper separation in the presence of arbitrary gravitational
fields, and shows that this ratio only corresponds to the purely dynamical result if the gravitational tide is
constant.
See [105*] and references therein, e.g., [27], for discussion of the details of the interpretation of redshift in an
expanding Universe. The first level of sophistication involves maintaining the GR principle that space is locally
Minkowskian, so that in a small region of space all effects must reduce to SR (for instance, in Peacock’s [155*]
example, the expansion of the Universe does not imply that a long-lived human will grow to four metres tall
in the next years). Redshift can be thought of as a series of transformations in photon wavelengths
between an infinite succession of closely-separated observers, resulting in an overall wavelength shift between two
observers with a finite separation and therefore an associated “velocity”. The second level of sophistication is
to ask what this velocity actually represents. [105] calculates the ratio of photon wavelength shifts between
pairs of fundamental observers to the shifts in their proper separation in the presence of arbitrary gravitational
fields, and shows that this ratio only corresponds to the purely dynamical result if the gravitational tide is
constant.
years). Redshift can be thought of as a series of transformations in photon wavelengths
between an infinite succession of closely-separated observers, resulting in an overall wavelength shift between two
observers with a finite separation and therefore an associated “velocity”. The second level of sophistication is
to ask what this velocity actually represents. [105] calculates the ratio of photon wavelength shifts between
pairs of fundamental observers to the shifts in their proper separation in the presence of arbitrary gravitational
fields, and shows that this ratio only corresponds to the purely dynamical result if the gravitational tide is
constant.