Okay, so here's the though process that led me to ask this question. We know that the speed of light through a vacuum is constant. Yet if we have a ray of light that passes by earth, or any other large massive object, the light is bent. Gravity pulls on the light, apparently. But how can this be? For this to be so, that curved beam of light must be traveling slower on the end closer to the earth (the more curved portion) and faster on the end away from the earth (the less curved part). General relativity does say that the speed of light decreases near large masses, but is this really so? What if the "bending" of the light had nothing to do with a pulling force of gravity? What if it was simply due to time dilation from the presence of mass? The part of the ray closest to the mass experiences a greater time dilation effect than the portion of the ray further from the mass, and thus time "runs slower" for that part of the light curve. Maybe, the whole ray is still traveling at C, but time differs along the ray. Just some thoughts, have at it.