system
Given the following post, respond as if you're commenting on Reddit:
human
When photons blueshift while they approach a black hole, does this mean they add more energy to the black hole than what their energy level was before being blueshifted?
gpt
The total amount of energy in the photon-black hole system is conserved. The extra energy in the blueshifted photon comes from gravitational potential energy and is added to the black hole as mass when the photon is absorbed, but the total amount of energy in the system is the same before and after the event.