When a photon travels cosmomogical distances, it gets a cosmological redshift. Easy to explane it when you think of it as the wavelength being stretched by expanding space, but what if you looked at this from an energy point of view? The energy that went in to creating the photon is smaller than the energy gained by absorbing the photon.
Eemit > Erecieve
Where did the energy go to? To me it seems that the concervation of energy principle is violated, Unless the energy lost by the photon was used to expand the space it moved trough.
ΔEnergy → Δspace
But if this is the case, why isn't all the space expanding? Only the intergalaxtic space seem to expand. (maybe innergalaxtic space is already stretched to the max (a sort of saturation), of gravity prevents it to expand)
For a moment let's assume that the energy loss is (in some degree) contributing to the expansion of space. Could this be a two way process? Could a low energy photon gain some energy when it travels trough expanded space, and in the process contract it a little? In that case a cosmological blueshift is possible for very low energy photons . In this perspective you could see space as the medium that nature creates to stores some of it's energy.
It's a complete crackpot idea, I know, but (to me) it's a fun one to think about. I just wanted to put it on the table for an open discussion, not as an ATM idea. I don't see it colliding with any mainstream theories (maybe it collides with GR, but GR is out of my comfort zone).