General Relativity: An Introduction for Physicists · Problem 13.23
The Kerr geometry — Hobson, Efstathiou & Lasenby
Physics · kerr-photon-redshift-sagnac
Problem
Which, if any, of the photons considered in Exercises 13.21 and 13.22 is redshifted from its original frequency on arriving back with Alice or Bob? Explain your reasoning.