So I was reading Stephen Hawking's book titled, 'A brief history of time, from the Big Bang to Black Holes' and in it, he talks about Galileo's experiment with rolling different weighted balls down a slope and seeing if the larger ones accelerated faster or not. Needless to say unrelated to the point of my thread, there was no difference in the speed of acceleration and they all accelerated at the same speed. (Approximately 1 meter per second per second, 2 meters per second per second, 3 meters per second per second and so on.) Anyways...

Now, this made me wonder, what if you had a slope that went on forever and had 0 friction, that was in an 'atmosphere' with 0 resistance of any kind. For example we'll say it used magnetic levitation to levitate the ball above the slope, and you were in a 100% complete vacuum. What would happen if you rolled the ball down the slope after a significant amount of time? (Yes, I know if you were in a 100% complete vacuum you wouldn't be able to, this is just a theoretic example) According to Einstein's theory of special relativity, and the laws of physics, nothing can go faster than light, due to resistance, as-well as his equation which demonstrates that the faster an object goes, the more mass it gains.

But, if there were no resistance from air or any kind of particles in the atmosphere, and there were no friction between the ball and the slope (maglev) what would happen after an infinite amount of time? Because if there is no friction or resistance, there is nothing from stopping the ball from gaining speed indefinitely - unless that's where Einstein's equation comes into play (Energy = mass times the speed of light in a vacuum squared) which details that, again, the faster you go the more mass you gain.