I don't think it'll be near as big as this is being made out to be. The speed of light is not constant, but is a function of the shape of spacetime in which it is traveling. This can be directly observed (or not) through blackholes. Now, the earth has nowhere near the mass to warp spacetime in such a way as a blackhole does, but none the less... the warping is there. The warpage will cause variance in the speed of light because of the 'time' traveled, not the distance. Think about light and particles in spacetime without mass effect as a straight line ----------->. Add a mass effect to warp spacetime and you end up with a curved line `'~._,~`> (hard to do w/ characters)... But imagine the start and end point of the particle is the same point in space, the only difference is a mass effect causing a bend in spacetime. What you have to realize in viewing this is that there is absolutely no difference in distance of those two lines. They are equal, even though they look different. It is actually the time function of spacetime that is twisted and bent by the mass. This causes a reduction in the speed of light. In a black hole, the speed of light is effectively 0 due to time dilation.
What I believe will be found is that the earth doesn't mass as much as we think it does, or perhaps some other mass disturbance in our general area is causing previously undetected disturbances in our local field.
