I was reading about redshift a few weeks ago and came to the understanding that the speed of light is not a constant in space. The only constant in space is the gravity in a vacuum. I also came to the basic understanding that when there is less gravity present that the force of gravity placed upon the photon, possibly through a process where the photo absorbs gravity which would be relative to how the mass of steel absorbs the heat during welding, would actually cause the photon to be less energetic thus causing the photon to travel at a rate slowler than the speed of light. When too much energy is absorbed by the photon the photon like a balloon is over inflated and pops. So in order for the photon to travel at light speed it has to absorb just the correct amount of gravity which the photon then emits back in the form of radiation seen as the visible light spectrum.