I was recently watching part 1 of the Nova special The Elegant Universe based on Brian Greene's book of the same name. It was mentioned that through Einstein we learned that Gravity travels at the same speed of light. What relationship exists between Gravity and Light that makes them travel at the same speed? Also besides the speed of light relationships between light and gravity, are there any other forces of nature that exist at this same speed? What aspect do all these things possess that make them travel at such a speed? Is it even known why light travels at the speed that it does? Thanks I know there are a lot of questions in here.