I know only the basics about relativity, and was explaining to my friend that as you travel at a speed that approaches c, you experience less time than an observer. I believed that it was explained in "A Brief History of Time" such that your 'velocity' vector can only have a magnitude of c, and if portions of that vector are are in the spatial dimensions rather than the time dimension then you won't experience as much time as an observer. So then my friend asked "well, if I rode Kingda Ka for 50 years straight, would I age at least 1 second less than you?" I have the feeling that it would have a negligible effect on his aging, and my prediction was that he would experience only millionths of a second less time than a relatively motionless observer would. Is there any equations for the layman that I could use to calculate something like this?