V.T31 — Gravitational redshift from tau-Einstein

A photon emitted at gravitational potential Phi_em and observed at Phi_obs experiences fractional frequency shift Delta nu / nu = (Phi_obs - Phi_em)/c^2, where Phi = -GM/r with G = (c^3/hbar) iota_tau^2. Confirmed by Pound-Rebka (1959) and Gravity Probe A (1976, 70 ppm).