My book says this:- So objects move slower actually means that we perceive them as slower. It is not "actually" moving slower. I interpret this is this way : Objects move at the same speed but since we depend on light to see objects, it seems as if they are moving slower as light takes longer. Am I right? Now this creates lot of confusion. In the famous twin paradox it is said that the twin ages more that the other. According to me, the aging for both is same but the still guy only perceives the other one to be slower i.e. light is taking more time to reach him. In this case both should be same age. I'm kind of lost here.