But, why is the speed of light finite? If you shove a stone of mass X and it goes flying off at speed V, then if you shove a stone of mass X/2 it’ll fly off at speed 2V. So, you might suspect that if you shove a stone of zero mass that it would go flying off at an infinite speed. If you think of infinite speed as how fast you’d be going if you accelerated forever, then the speed of light is exactly that. Q: Why is the speed of light the fastest speed?