I have figured out that:
- When photons leak out from a container, the entropy of the photon collection increases, because each photon has a different escape time.
- Photons that have leaked out from a container can be collected into a container of the same size, if that container is in a gravity well deep enough.
- When photons fall some distance in a gravity field, each photon's energy becomes multiplied by some factor, which does not change the entropy.
- After aforementioned container has been winched up from the gravity well, the entropy of the photons inside must be increased compared to the entropy of the photons inside the first leaky container.
So I suspect that lifting some radiation increases its entropy. Am I on a right track here?
I have a suggestion how the entropy increases when a cube-shaped mirror walled container of radiation is lifted: A photon moving into just right direction does not touch the floor or the ceiling of the container during the lifting process. The lifting agent does not do any work on that photon. Work done on a photon ranges from zero to X joules, which increases entropy. When gravity does work on photons, every photon's energy increases by K percents, which does not increase entropy.
Clarification to point 2: Observer in the gravity well sees the radiation to leak out rapidly. The short time implies small entropy increase. Observer outside the gravity well sees that radiation slows down when the radiation enters the gravity well. The line of photons contracts when photons at the front are slowing down.
Oh yes, optically dense material has the same effect as gravity well. And also if a photon catcher device moves rapidly towards the photons, then photons go in rapidly and come out slowly, which allows an arbitrarily large photon gas cloud to be caught into a small volume container, in this process temperature of radiation increases without entropy of radiation increasing.