Einstein's Theory of Relativity. The speed of light is the absolute speed limit of the universe because space and time will warp to extreme lengths in order to preserve that limit. In order for an object with mass to move at the speed of light it must have infinite energy due to space increasing its effective mass as it accelerates to the speed of light. Additionally, time slows down as a object approaches the speed of light. As such, time comes to a standstill at lightspeed. TL;DR: The universe does everything in its power to keep you from reaching lightspeed.