HI, i don't understand a lot of things about relativity so I will write the things I am confused about and maybe someone can helop me 1. How can light be forced to go slower than a certain speed if space is empty? To me it looks like light rays are pieces of luggage falling on one of those moving conveyor belts or something. doesn't matter how fast you throw them on it they all end up going the same speed But if a star is moving at 1/2 the speed of light then you could also look at it like the star is not moving and the universe is moving past at 1/2 the speed of light, but if space is empty and doesn't effect light-speed it would still travel away from the star at light spee, so to the rest of us it would travel at 1 1/2 times the speed of light. but it doesn't so there is something that is slowing the light from the star and the force is exactly the same as the amount it's speed goes over the speed limit. a really big coincidence! how does it work? 2. Is it true that gravity can change the wavelength of light but not it's speed? 3. DOesn't light slow down in water thenhow do we know that space is really completely empty and that there are some things that slow it down even just a little? 4. e=mc2 i know kind of what this means but i don't know how it works. mass times the speed of light squared, so it's kind of like the same force of the speed light working against itself times something's mass gives you it's energy. but why does it work? why does the speed of light have anything to do with mass or energy? 5. what are the measurements? if something weighs 10 kilograms then you times it by 300 000 kilometres? and end up with watts or something? Well, those are my questions. I hope someone knows the answers here.