Light travels as waves through space, and since space is expanding, the light gets stretched out. This is the explanation for red shifting I learned before.
Now I know some more and that explanation isn't good enough.
- The longer wavelength light that would result from red shifting has lower energy.
- Total energy in the system must be conserved, so the amplitude of the light must be higher after red shifting.
- As per quantum mechanics, light exists as discrete photons. The loss of energy must be instant, and at the same time, more photons must be created so the total energy is conserved.
So this photon "splitting" explanation sounds okay, but it still seems problematic. Photons can split (like here), but a photon cannot split on its own in a vacuum, as far as I know.
Perhaps some assumption I made here is wrong.
What is the explanation for red shifting that agrees with quantum mechanics?
I'm not very familiar with relativity, I may have missed some phenomenon in relativity that explains all this.