How do define if something is moving or not? I mean isn't it friction, attraction, repulsion, etc. which causes something to slow down or speed up? Also by reference pt., we make judgment. But if there is an object, only by itself in the space, how would you know if its moving at 3x the speed of light or not? Why is moving at the speed of light impossible?(I know it requires infinite energy but why? B/c it gains more mass? But why does it gain more mass? the faster something travel, the thinner and longer and slimer it gets, why? Why does time slows down the faster we move?