I know there is an answer to this somewhere, so please forgive me for not being able to see it :) When people say that light will always be measured at a constant speed, no matter where you are, what do they mean? Say we are in a spaceship which is standing still. Inside the spaceship, we throw a ball at 5 m/s. Now the spaceship goes to a fast speed. We throw the ball, and inside the ship, we still see it as 5 m/s. So are they saying that if you are in the fast-moving spaceship, you will measure light the same as in the standing still space ship, just as you would the ball? That doesn't make any sense, because that would imply that light, like the ball, is affected by the inertia of the ship. It also implies that if the ship is moving at 100 m/s and the ball is 5 m/s from inside the ship, then to the outside, the ball is 105 m/s. Thus, if the light was also affected, then that means that the light would be going at c+5 m/s to the outside observer. You see where I have this confusion? Thanks.