Doesn't the speed of light contradict the first law of thermodynamics (energy can't be created or destroyed)?
Let's say a super advanced civilization lets a spaceship orbit around a black hole. It beams energy to it via microwaves, and the ship transforms that energy into acceleration. At some point though, it will simply not accelerate anymore. The energy that is being sent, is therefore not transformed anymore, but destroyed. E.g. you could not re-harvest it by re-transforming the kinetic energy of the ship's velocity. E.g. the energy is gone forever, which by the first law of thermodynamics is impossible.