The Importance of Mass in Relativity

A lot of people think of mass is like the amount of stuff they have and so it's really weird for them to imagine them getting more as they approach the speed of light. I don't like this concept of relativistic mass because it gives people the impression that something physical is happening which isn't. All right a lot of great answers here. I feel like some people were blown away and some people were like oh I've heard of this. The answer is yes or no. Yeah I thought this was really interesting. There's a lot of different ideas here about what energy is and what mass is.