I apologize if this has been covered but I did a quick search and didn't see anything. Alright, my question concerns the speed of light and why it's a constant. I was trying to explain special relativity to my friend and after I told him that the speed of light is always c no matter what reference frame you are in he seemed troubled by the idea. He gave me an example of how this could not be, here is what he said: "alright say light and I start at the same point and I'm going .8c along side it, you're meaning to tell me that light is still going c even though it should be going .2c?" I simply said yes, he asked why. I tried to say that the speed of light has to be constant so no reference frame was special and every reference frame in uniform motion is good for doing physics. He still went back to his example though, it's actually a pretty solid argument. I'm new to relativity so I'm having trouble explaining to him. Can someone help me explain this?