Can someone or approve or disapprove my question. I want to make sure I get this right. I will use Bill & Nancy as observers and friends For example, if Bob is going at the speed of light inside a spaceship, his mass will increase indefinite but he will not notice the effects. Bob will notice no changes of himself inside the spaceship. However Nancy is outside on a Asteroid outpost building and Notice her friend Bill traveling at the speed of light. Nancy could not believe her own eyes. Bill has grown way to huge of infinity amount. However Bill also notices Nancy. Bill also could not believe his eyes. Nancy has grown infinite in size when he was passing her up at the speed of light while Nancy was waving hi to him on the asteroid outpost. Nancy will also see herself as everything being normal with no increase in Mass. Did I get this story right? Is it safe that I got this relatively rule right?