What happens as waves move through the EM spectrum?

Question

EM waves don't travel through a medium, however light waves change color as they move farther away or closer. (Red shift, blue shift) What happens to the energy these waves used to carry. So if a gamma ray goes for a long time, will it eventually change to light? And if so, how does it take place and where does the energy it had go? Eventually the wavelength will be longer than a radio wave and then what do we have? Will it eventually disappear?

Answer 1

As far as I know the wavelength of a traveling photon doesn't shift unless you're moving relative to the source or the photon changes gravitational potential.  If the photon goes up or down in a gravitational field the energy transfers from wavelength to gravitational potential.  I think the speed of the photon also changes at different points of gravitational potential.

Answer 2

The  answer depends on the precise conditions of the event. Light waves emitted by a source will have larger energy as the source moves toward us than when the source moves away, but the photons  emitted in the first case are not the same ones as in the second case, so nothing has "happened" to them.  However (and now I'm talking about a different situtation) a photon traveling past us will have the same energy when it travels towards us as when it travels away from us, because it's the same photon.

I believe the same type of argument applies to the cosmological redshift.  A given photon does not change its color once it is emitted.  Those with largest red shifts were emitted by galaxies farther away in the universe, which move more rapidly.