Let's say that the speed of light is pushed by gravitational fields. This would mean that the speed of light is only equal to c relative to the gravitational field that the light is traveling through. So if you had a device that is stationary on the surface of the Earth, the speed of light would be constant in that device because the device is stationary in the Earth's gravitational field (the Earth's field spins with the Earth). If an object is moving through a gravitational field, the speed of light, relative to that object, would decrease or increase depending on the direction of the light in that object. However, the average speed of light (in all three dimensions) of light in that object would decrease. The decrease in the average speed of light in that object would cause the reactions in that object to slow down since the reactions are dependent on the speed of light. If my model is correct, it would not only replace relativity, but it would also explain photon propulsion.