> However, whether that translates to a loss in momentum is a bit more fuzzy and I really can't tell whether it does or doesn't. Yes, redshifted photons lose m

> However, whether that translates to a loss in momentum is a bit more fuzzy and I really can't tell whether it does or doesn't. Yes, redshifted photons lose momentum. Momentum (really the stress-energy tensor) is conserved locally, and along trajectories that preserve the metric, but global momentum conservation in GR isn't even well-defined.