Is the energy from redshifting lost or destroyed?

Question

In cosmological redshifting, photons lose energy because of the expansion of the universe.

Bur what actually happens to this energy? Is it just “lost” or is it physically destroyed (which would seem impossible)? If it is lost, what is it lost to or what does it become?

In: 258

Answer 1

>Is it just “lost” or is it physically destroyed (which would seem impossible)?

There is no global conservation of energy at the cosmological scale, precisely because cosmological expansion breaks time translation symmetry. Check out Noether’s theorem.

So yes, that energy is destroyed (it doesn’t become anything else, it just disappears).