system
Given the following post, respond as if you're commenting on Reddit:
human
When a photon is red-shifted, (how) does it lose energy?
gpt
momentum, and therefore energy  change based on frame of reference. a baseball thrown at 100 miles an hour has a decent amount of energy relative to a "static" observer, but if you were to drive by the pitcher  in a car at 100 miles an hour, the ball would essentially be still in your frame of reference and have no kinetic energy. similarly, if you were to accelerate towards a redshifted lightsource in a rocket ship, you'd eventually reach a point where the light is no longer redshifted, since you and the light source are still relative to each other.