In six Level 1 videos we visualize General Relativity with a substratum (“fabric”) that uses the same math as GR, the math of curved surfaces.
Here in part 3 of 6: Locally, we always measure the speed of light to be 1. Over distance, we measure it to be less than one. We also see how a gradient of light speed causes light to bend toward slower light. A breather (soliton) accelerates toward slower light.