We don't. There is no “speed of light”, it's a misunderstanding to assume that there is one.

What really happens is the following: light is an instantaneous effects in the universe, but the universe is computing at a speed limit, which we call “celerity” (“c”), which means “speed” (300.000.000 meters per second is quite a speed).

So “c” is more precisely defined as being the speed of time. Because everything that is not moving in time is computed at this speed.

Light teleports in space and in time, so light does not experience space nor time. For light in the universe, there are no distances, light instantaneously teleports from start location to destination (no time has passed).

Gravity is also propagated at this speed. And we don't know about that because of the scale of things, but we can assume that weak and strong nuclear forces are also computed at this speed.

Therefore you can't exceed that speed, in any way. Please understand what time is: it's a computation, a change, without it the universe would contain no motion, no modification, no change. Frozen to death.

In time, something and only, is preserved: energy. Nothing (=”no thing”) could roll back time, because this would imply an energy shift and that, as far as we know, could only be called a “Big Bang"…